Doc #163 — Housing Insulation Retrofit and Heating Adaptation

---

RECOMMENDED ACTIONS (BY ACTUAL URGENCY)

First two weeks

1. Issue public guidance: close curtains, seal visible draughts, wear warm clothing indoors, consolidate household members into fewer rooms. These cost nothing and reduce heat loss immediately.
2. Classify insulation material supply chains as essential: wool scouring facilities, sawmills, existing insulation manufacturers.
3. Begin planning the retrofit programme — identify institutional lead (likely MBIE or a dedicated housing unit under Civil Defence).

First month

4. Activate community heated spaces in every town and city — marae, community halls, churches, schools, libraries. These serve as immediate warming centres for the most vulnerable (Section 8).
5. Begin national housing stock assessment — prioritise identifying the worst-performing houses occupied by elderly and families with young children. Use existing council and health data as a starting point.
6. Secure all existing manufactured insulation stocks (fibreglass, polystyrene, polyester) at retailers and warehouses. Allocate to highest-priority retrofits.
7. Issue guidance to wool industry: divert crossbred wool from export stockpiles to insulation production. Coordinate with scouring plants (see Section 5.1).
8. Begin draught-proofing material production — foam strip alternatives from wool felt, rubber offcuts, fabric strips.

First three months

9. Establish wool insulation production at scale — scouring, treatment, batt or loose-fill production at existing wool processing facilities (Section 5.1).
10. Establish sawdust and wood shaving collection from all operating sawmills for loose-fill insulation (Section 5.3).
11. Begin training retrofit installation teams — based on Warmer Kiwi Homes contractor training experience, the physical installation tasks are learnable within 3–5 days of supervised practice for workers with basic construction familiarity, but organised instruction on ceiling access, underfloor work, vapour management, and electrical hazard avoidance (especially around downlights) materially improves outcomes.⁷
12. Begin retrofitting the highest-priority houses: those with no ceiling insulation occupied by elderly persons or families with children under five.
13. Distribute secondary glazing and thermal curtain guidance. Begin community production of thermal curtains from wool fabric and blankets.

First year

14. Mass retrofit programme operational — targeting ceiling insulation first (highest return per unit of effort), then underfloor, then walls.
15. Wool insulation production at 10,000+ tonnes per year (see Section 5.1 for feasibility).
16. Community heated spaces operational in all significant population centres.
17. Heat pump maintenance programme established to extend the life of NZ’s existing installed fleet.
18. Firewood supply chain formalised for regions dependent on wood heating (Section 4.3).

Years 2–5

19. Continue mass retrofit — target all occupied dwellings with substandard insulation.
20. Wall insulation where feasible (this is harder and slower than ceiling and underfloor).
21. Secondary glazing programme for worst-performing windows.
22. Monitor health outcomes — adjust programme targeting based on actual mortality and morbidity data.

---

ECONOMIC JUSTIFICATION

The cost of cold houses

Under normal conditions, cold housing is estimated to cost NZ approximately $50–150 million per year in excess health expenditure — hospital admissions for respiratory and cardiovascular illness, GP visits, pharmaceutical costs — plus unquantified costs in lost productivity, school absences, and reduced quality of life.⁸ Excess winter mortality in NZ under normal conditions is estimated at 1,600 deaths per year, with a significant fraction attributable to cold, damp housing.⁹

Under nuclear winter conditions, these figures increase substantially. A 5–8°C cooling applied to NZ’s existing housing stock — without intervention — would plausibly double or triple excess winter mortality, particularly among the elderly. This is an estimate based on the established relationship between indoor temperature and health outcomes (Section 3), extrapolated to more severe conditions. The actual outcome depends on how quickly and effectively NZ responds.

The cost of retrofit

Labour: Ceiling insulation retrofit for a typical NZ house takes 2–4 person-hours for an experienced team of two workers. Underfloor insulation takes 4–8 person-hours depending on access.¹⁰ At these rates, retrofitting ceiling insulation in 500,000 houses (a rough estimate of the highest-priority dwellings) requires approximately 1–2 million person-hours, or roughly 500–1,000 person-years. This is a significant labour commitment but modest relative to the total recovery workforce. For comparison, Doc #3 estimates that destocking operations alone require tens of thousands of person-days.

Materials: Wool insulation at approximately 10–15 kg per square metre of ceiling area, for an average ceiling of approximately 100 m², requires approximately 1,000–1,500 kg per house. For 500,000 houses, total wool requirement is approximately 500,000–750,000 tonnes — this exceeds one year’s clip. However, not all houses need full wool insulation: many already have partial insulation that needs topping up (perhaps 200–500 kg per house), and alternative materials (sawdust, straw, recycled paper) can supplement wool supply. A blended materials approach makes the programme feasible within 2–3 years.

Materials cost in recovery terms: The raw materials are essentially free in economic terms — crossbred wool has very low export value even under normal conditions, and under recovery conditions its only competing use is textile production (Doc #36), which requires a different grade and processing chain. Sawdust and wood shavings are byproducts of timber milling. Straw is an agricultural byproduct. The real cost is labour and transport, both of which are finite recovery resources.

Labour availability note: Insulation installation is general construction work that can be learned in 2–5 days of supervised practice and does not require scarce specialist skills (unlike, for example, electrical or plumbing work). The main training requirements are safe ceiling access, working in confined underfloor spaces, correct coverage technique, and awareness of electrical hazards (downlights, wiring). In a recovery economy with widespread unemployment from disrupted industries, the labour pool for this work is large, and deploying people into useful, visible community work has direct benefits for social cohesion and mental health beyond the thermal improvement itself.

Return on investment

Insulation reduces heating energy demand by 30–50% in a poorly insulated house — a well-established figure from NZ retrofit studies.¹¹ Under nuclear winter, where heating demand is much higher than normal, the absolute energy saving is correspondingly larger. Every house insulated reduces the firewood that must be harvested, transported, and burned, or the electricity consumed by heat pumps. It reduces the load on the electricity grid. It reduces hospitalisations. It reduces deaths.

Breakeven: Insulation pays for itself within the first winter in health cost avoidance and energy savings. Insulation is one of the highest-return resource allocations available to the recovery. The Motu Economic and Public Policy Research evaluation of the Warm Up New Zealand programme (the predecessor to Warmer Kiwi Homes) estimated a benefit-cost ratio of approximately 3.9:1 (with a range of approximately 2.5:1 to 5.5:1, depending on assumptions about the value of reduced mortality) for ceiling and underfloor insulation under normal conditions.¹² Under nuclear winter conditions, with higher heating costs and greater health impacts from cold housing, the ratio is likely higher — though the exact multiplier depends on the severity of cooling and the effectiveness of the retrofit programme at reaching the most vulnerable households.

Opportunity cost

The workers installing insulation could be doing other things — agriculture, infrastructure repair, manufacturing. The question is whether insulation is a better use of their time than alternatives. Given that the health consequences of cold housing directly reduce the workforce available for all other recovery tasks (sick people cannot work; dead people cannot work at all; carers for sick family members are diverted from other tasks), insulation is a force multiplier — it preserves the labour supply for everything else.

---

1. NZ’S HOUSING STOCK: THE PROBLEM

1.1 Scale and age

NZ has approximately 1.8 million occupied dwellings.¹³ The housing stock is predominantly:

• Timber-framed: NZ houses are almost universally light timber frame with weatherboard, brick veneer, or sheet cladding. This construction type is amenable to insulation retrofit (cavities exist for insulation material, and ceiling and underfloor spaces are typically accessible) but performs poorly when uninsulated (timber framing has minimal thermal mass and the wall and ceiling cavities allow air circulation that transfers heat rapidly).
• Single-storey or two-storey: Most NZ houses are single level or split-level, with accessible ceiling spaces (important for retrofit) and often accessible underfloor spaces (suspended timber floors over a crawl space).
• Old: Approximately 800,000 dwellings were built before 1978, when NZ introduced its first insulation requirements in the building code (NZS 4218). Many of these have no insulation at all, or insulation that has degraded, compressed, or been removed.¹⁴ A further 400,000–500,000 were built between 1978 and 2000 under insulation standards that, while better than nothing, were well below current requirements and far below standards in comparable-climate countries.¹⁵

1.2 Thermal performance

BRANZ (Building Research Association of New Zealand) has conducted extensive research on NZ housing thermal performance. Key findings:¹⁶

• Indoor winter temperatures: The median winter living room temperature in NZ houses is approximately 16°C — well below the World Health Organisation’s recommended minimum of 18°C for health, and below the 21°C considered comfortable in most international standards.¹⁷ Bedrooms and other rooms are typically colder, often 12–14°C.
• Uninsulated houses: Houses with no ceiling insulation — still a significant minority — typically have winter living room temperatures of 12–15°C even with heating, because heat is lost through the ceiling as fast as it is generated.
• Heat loss pathways: In a typical uninsulated NZ house, heat loss is approximately: ceiling 30–35%, walls 20–25%, floor 10–15%, windows 15–20%, air leakage (draughts) 15–25%.¹⁸ These proportions vary with house design but the ceiling is consistently the largest single loss pathway in single-storey houses.
• Air leakage: NZ houses are exceptionally draughty by international standards. Blower door tests show air change rates of 10–20 air changes per hour at 50 Pa (ACH50) for older NZ houses, compared to 3–5 ACH50 for well-sealed modern houses in cold-climate countries.¹⁹ This air leakage carries heated air out and cold air in, bypassing insulation.

1.3 The pre-existing health burden

Cold, damp houses are already a major public health problem in NZ:

• Excess winter mortality: NZ has one of the highest excess winter mortality rates in the developed world — approximately 1,600 additional deaths per winter compared to the non-winter baseline, a rate comparable to countries with much colder climates but better-insulated housing stock (Sweden, Norway).²⁰ This is primarily cardiovascular and respiratory mortality among the elderly.
• Respiratory illness: Cold, damp housing is strongly associated with respiratory infections, asthma exacerbation, and chronic obstructive pulmonary disease (COPD). The Housing, Insulation and Health Study (University of Otago) demonstrated that insulating NZ houses reduced self-reported cold and flu symptoms, GP visits, and days off school and work.²¹
• Child health: Children in cold, damp houses have significantly higher rates of hospitalisation for respiratory illness, asthma, and related conditions. NZ’s child asthma rates are among the highest in the world, and cold housing is a significant contributing factor.²²
• Equity: The burden falls disproportionately on low-income households, Maori and Pasifika families, the elderly, and renters — groups that are less able to afford heating or retrofitting and more likely to live in poorly insulated older housing.²³

---

2. NUCLEAR WINTER IMPACT ON INDOOR CONDITIONS

2.1 Temperature scenarios

The Recoverable Foundation working paper estimates approximately 5–8°C of average cooling for NZ under the modeled nuclear winter scenario (4,400-warhead exchange).²⁴ This is a year-round average with seasonal variation persisting — winters become approximately 5–8°C colder than current winters, and summers approximately 5–8°C colder than current summers.

Current NZ winter temperatures (approximate June–August averages):

Location	Average daily minimum	Average daily maximum
Auckland	8°C	15°C
Hamilton	4°C	13°C
Wellington	6°C	12°C
Christchurch	1°C	11°C
Dunedin	2°C	10°C
Invercargill	1°C	9°C

Source: NIWA climate summaries.²⁵

Under 5–8°C additional cooling:

Location	Adjusted daily minimum	Adjusted daily maximum
Auckland	0 to 3°C	7 to 10°C
Hamilton	-4 to -1°C	5 to 8°C
Wellington	-2 to 1°C	4 to 7°C
Christchurch	-7 to -4°C	3 to 6°C
Dunedin	-6 to -3°C	2 to 5°C
Invercargill	-7 to -4°C	1 to 4°C

These adjusted temperatures are rough estimates, applying the cooling uniformly across the year, which is a simplification — actual nuclear winter effects may produce non-uniform seasonal shifts. But the order of magnitude is clear: NZ’s South Island experiences regular sub-zero minima, and even Auckland sees winter minimum temperatures near freezing.

2.2 Indoor temperature consequences

Indoor temperature in an unheated house tracks outdoor temperature with a lag and some buffering from thermal mass (the house structure absorbs and releases heat). In a house with no heating and no insulation, indoor temperatures stabilise at roughly 2–5°C above average outdoor temperature due to incidental gains (body heat, cooking, solar gain through windows).²⁶

Under nuclear winter conditions:

• Uninsulated, unheated house in Christchurch: Average indoor temperature approximately -2 to 4°C in the coldest months. This is life-threatening for prolonged habitation.
• Uninsulated, unheated house in Auckland: Average indoor temperature approximately 5–10°C. Deeply uncomfortable, health-damaging, but survivable for healthy adults.
• Insulated, heated house anywhere in NZ: With adequate ceiling, underfloor, and wall insulation plus moderate heating input, indoor temperatures of 14–18°C are achievable even under nuclear winter conditions. The heating energy required is roughly 2–3 times normal NZ winter levels (based on the degree-day relationship: a 5–8°C average cooling increases heating degree-days by approximately 60–120% for most NZ locations), an increase that is large but within the capacity of NZ’s electricity supply and forestry resources provided demand management is in place (Doc #67).²⁷

Functional implication: The gap between an insulated and an uninsulated house under nuclear winter conditions determines whether occupants face manageable discomfort or clinically dangerous cold exposure. For elderly occupants and children under five — the groups most sensitive to sustained low indoor temperatures (Section 3.2) — inadequate insulation translates directly into increased hospitalisation and mortality.

2.3 Duration

Nuclear winter effects are expected to persist at full severity for approximately 2–5 years, with gradual easing over years 5–10.²⁸ This means NZ faces multiple winters at these extreme conditions — not a single event. A retrofit programme that takes 2–3 years to implement across the most vulnerable housing stock will provide protection for the worst winters if begun promptly.

---

3. HEALTH IMPACT OF COLD HOUSING

3.1 The temperature-mortality relationship

The relationship between indoor temperature and health outcomes is well-established in the international literature and specifically studied in NZ:²⁹

• Below 16°C: Respiratory function is impaired. Risk of respiratory infection increases.
• Below 12°C: Cardiovascular stress increases. Blood pressure rises as the body attempts to maintain core temperature through vasoconstriction. Risk of heart attack and stroke increases, particularly for the elderly and those with pre-existing cardiovascular disease.
• Below 9°C: Risk of hypothermia for sedentary individuals (the elderly, infants, those with limited mobility). Prolonged exposure causes progressive core temperature decline.
• Below 5°C: Serious hypothermia risk for all occupants. Sustained habitation at these indoor temperatures without adequate clothing and bedding is dangerous.

3.2 Vulnerable populations

The health impact of cold housing is not distributed evenly:

• Elderly (65+): The most vulnerable group. Thermoregulation declines with age. Cardiovascular and respiratory disease prevalence is highest. Mobility may be limited (reducing heat generation from activity). NZ’s over-65 population is approximately 850,000.³⁰ Many live alone in older, poorly insulated houses.
• Infants and children under 5: Limited thermoregulatory capacity. Respiratory illness susceptibility is high. Approximately 300,000 children under 5 in NZ.³¹
• People with chronic illness: COPD, asthma, cardiovascular disease, diabetes — all are exacerbated by cold exposure. These groups are disproportionately represented among NZ’s low-income and elderly populations.
• Maori and Pasifika communities: Higher rates of overcrowded and poorly insulated housing, higher rates of respiratory illness, higher rates of child hospitalisation for cold-related conditions.³² These communities also have strong whanau and community support structures that can be leveraged for collective retrofit and shared heating solutions.

3.3 Estimated excess mortality without intervention

Under normal conditions, NZ’s excess winter mortality is approximately 1,600 per year.³³ Under nuclear winter conditions, with 5–8°C additional cooling applied to the existing housing stock and without a retrofit programme:

• Excess winter mortality could plausibly increase to 3,000–6,000 per year, primarily among the elderly and those with chronic disease. This is an estimate based on the known temperature-mortality relationship, not a modeled prediction. The actual figure depends heavily on how effectively NZ responds.
• Hospitalisations for respiratory and cardiovascular illness would increase correspondingly, placing additional strain on a health system already stressed by import loss (Doc #116, Doc #4).
• Child illness would increase substantially, with downstream effects on childhood development and parental availability for other recovery tasks.

A significant fraction of this excess mortality is preventable with known interventions. Insulation, draught-proofing, community heated spaces, and maintained heating systems have established evidence bases for reducing cold-related mortality and morbidity in NZ (see Section 9.1, footnote 18). The remaining question is whether NZ implements them at sufficient scale and speed.

---

4. HEATING OPTIONS AND DEPENDENCIES

4.1 Heat pumps

NZ has an estimated 450,000–500,000 heat pumps installed in residential dwellings — a substantial fleet that has grown rapidly since the early 2000s.³⁴ Heat pumps are the most energy-efficient form of electric heating, delivering 2.5–4 units of heat per unit of electricity consumed (coefficient of performance, or COP) under normal NZ conditions.

Nuclear winter performance: Heat pump efficiency declines as outdoor temperature drops. A typical residential air-source heat pump (the dominant type in NZ):

• At 7°C outdoor: COP approximately 2.5–3.5, depending on unit age and model (delivers 2.5–3.5 kW of heat per 1 kW of electricity)
• At 0°C outdoor: COP approximately 2.0–2.5
• At -5°C outdoor: COP approximately 1.5–2.0
• At -10°C outdoor: COP approximately 1.0–1.5, and some units may struggle to operate or defrost effectively³⁵

Under nuclear winter conditions, NZ’s South Island experiences regular sub-zero outdoor temperatures. Heat pumps will continue operating at sub-zero temperatures — modern inverter units are rated to -15°C or below — but their efficiency advantage over direct electric heating (resistive heaters, which have a COP of 1.0) diminishes significantly at low outdoor temperatures. At -10°C outdoor, the COP advantage over resistive heating is small for older fixed-speed units, though modern cold-climate inverter units maintain better performance. In the North Island, where outdoor temperatures remain above -5°C for most of the heating season, heat pumps retain a meaningful efficiency advantage.³⁶

Dependencies: - Electricity supply: Heat pumps require grid power. Under the baseline scenario, the grid continues operating (Doc #67). Individual heat pump consumption is modest (1–3 kW per unit), but aggregate demand across hundreds of thousands of units during winter peak represents a significant grid load. - Refrigerant: Heat pumps contain fluorocarbon refrigerant that slowly leaks and eventually needs recharging. NZ imports all refrigerant. As stocks deplete, heat pumps that develop leaks cannot be repaired and must be retired. The fleet will decline over time — perhaps 5–15% per year from refrigerant-related failures, though this estimate is uncertain and depends on the age and maintenance history of individual units.³⁷ - Electronic components: Heat pump controllers and inverters contain electronic components that fail over time. Repair is possible for some faults (capacitors, contactors) but not for failed circuit boards without imported replacements. This is the same electronic degradation challenge facing all NZ equipment (Doc #130). - Filters and maintenance: Dirty filters reduce efficiency by 5–15%. Regular cleaning (monthly during heavy use) extends performance. This maintenance requires no imported parts — filters are washable and reusable.

Assessment: Heat pumps are a valuable heating asset for the first 5–15 years. They should be maintained and operated as long as possible. But the fleet will shrink over time, and NZ must plan for heating without them.

4.2 Electric resistive heating

NZ has large numbers of electric resistive heaters — panel heaters, fan heaters, oil-column heaters, night-store heaters — in addition to heat pumps. These devices contain no refrigerant and minimal electronics (a thermostat and, in fan heaters, a small motor). A resistive heater converts electricity directly to heat via a resistance element. These devices have a COP of 1.0 (one unit of heat per unit of electricity) and are less efficient than heat pumps, but they are more robust, repairable with common workshop skills (replacement elements can be wound from nichrome or similar resistance wire), and will last much longer than heat pumps under recovery conditions.

Under nuclear winter conditions, with heat pumps operating at reduced COP, the efficiency gap between heat pumps and resistive heaters narrows. In the South Island at sub-zero temperatures, the gap may be minimal.

The grid can support electric heating. NZ generates approximately 42,000 GWh of electricity per year, of which residential consumption is roughly 12,000–13,000 GWh.³⁸ Peak winter demand under normal conditions is approximately 6,500–7,000 MW. Under nuclear winter conditions, increased heating demand could push peak demand to 8,000–10,000 MW — a significant but potentially manageable increase, particularly if the Tiwai Point aluminium smelter is closed (freeing approximately 570 MW of baseload capacity — see Doc #109).³⁹ Load management and demand reduction through insulation are essential to keeping peak demand within grid capacity.

4.3 Wood heating

NZ has approximately 600,000 dwellings with a wood burner or open fireplace.⁴⁰ This is a substantial base of installed wood-heating capacity, and it does not depend on the electricity grid.

Firewood supply: NZ’s plantation forests produce approximately 30 million cubic metres of roundwood per year.⁴¹ Firewood demand, even under nuclear winter conditions, would be a fraction of this — perhaps 3–5 million cubic metres per year for residential heating (a rough estimate based on approximately 600,000 wood-heated dwellings consuming 5–8 cubic metres of firewood per winter).⁴² This is well within sustainable harvest capacity.

Challenges: - Chimney infrastructure: Many modern NZ houses (post-1990) were built without chimneys or flues. Installing a new wood burner or flue requires penetrating the ceiling and roof — feasible but not trivial, and must be done correctly to avoid house fires. Under recovery conditions, a streamlined approval process and standardised installation guidance would be needed. - Air quality: Concentrated wood burning in urban areas produces particulate air pollution. This is already a significant problem in NZ towns (Christchurch, Nelson, Timaru, Rotorua) under normal conditions.⁴³ Under nuclear winter conditions, with increased wood burning and potentially reduced atmospheric dispersion (cold, stable air masses), urban air quality could deteriorate substantially. This is a genuine health trade-off — wood smoke causes respiratory illness, which is the same category of harm that cold housing causes. The net health effect depends on the specifics, but in general, a warm house with some ambient wood smoke is healthier than a cold house without it. - Transport: Firewood is heavy and bulky. Moving it from forest to house requires vehicle transport, which requires fuel. Localised firewood supply — using nearby shelter belts, urban trees, and small woodlots — reduces transport demand. - Drying: Green (freshly cut) wood burns poorly and produces excessive smoke and creosote. Firewood should be split and air-dried for 6–12 months. Under nuclear winter conditions (cooler, more humid), drying takes longer. This means that firewood preparation must begin well before it is needed — ideally in Phase 1, for use from Phase 2 onward.

Firewood and the charcoal programme: Doc #102 describes charcoal production from NZ forestry. Charcoal production and firewood supply draw on the same forest resource but there is no supply conflict — NZ’s forestry surplus is large enough for both (Doc #102, Section 6.3).

4.4 Other heating options

• Gas heating: NZ has natural gas from Taranaki, distributed by pipe in parts of the North Island. Gas heating is efficient and effective but the gas supply is a finite resource that must be allocated across competing uses (industrial, cooking, heating). Gas heating may continue for those with existing connections but should not be expanded given competing demands on a depleting resource.
• Coal heating: Domestic coal burning is possible in areas near coalfields (West Coast, Waikato). Coal produces excellent heat but also significant pollution. A minor contributor to the national heating picture.
• Passive solar: Under nuclear winter conditions, solar gain through windows is reduced by an estimated 10–30%, depending on the severity and duration of stratospheric soot loading — the lower end corresponds to the later years of nuclear winter as particles settle, the upper end to peak-severity years 1–3.⁴⁴ NZ houses are generally not oriented or designed for passive solar gain, but north-facing windows still provide meaningful daytime heat gain even under reduced sunlight. Thermal curtains (Section 6.2) should be opened during sunny periods (especially on north-facing elevations) and closed as soon as the sun is off the window.

---

5. INSULATION MATERIALS FROM NZ RESOURCES

5.1 Wool insulation

Wool is NZ’s most important insulation material under recovery conditions. The country’s sheep flock produces approximately 120,000–140,000 tonnes of greasy wool per year under normal conditions, predominantly crossbred wool (strong wool) from meat-breed sheep.⁴⁵ This wool has low commercial value for apparel — its primary markets are carpets and industrial textiles, both of which are largely export-dependent. Under recovery conditions, crossbred wool becomes available in large quantities for insulation.

Properties: Wool is an excellent insulation material. Its thermal conductivity is approximately 0.035–0.040 W/m·K, comparable to fibreglass batts (0.035–0.045 W/m·K) and better than many natural alternatives.⁴⁶ Wool also has unique advantages:

• Moisture buffering: Wool can absorb up to 30% of its weight in water vapour without feeling wet or losing significant insulation performance. This is particularly valuable in NZ’s humid climate, where moisture management in building cavities is a significant challenge. Fibreglass, by contrast, performs poorly when wet.⁴⁷
• Fire resistance: Wool has a high ignition temperature (~570°C) and self-extinguishes when the ignition source is removed. It does not melt or drip like synthetic insulation materials. It produces less toxic smoke than synthetics when burned.⁴⁸
• Durability: Wool insulation retains its loft and performance over the long term (commercial manufacturers claim 50+ years for treated product, though field verification over such periods is limited). It does not slump or compact as readily as some loose-fill materials. However, untreated wool is vulnerable to moth and carpet beetle damage — see treatment requirements below.
• Air quality: Wool fibre can absorb certain indoor air pollutants including formaldehyde — the keratin protein in wool binds formaldehyde molecules irreversibly.⁴⁹ It does not release irritant fibres during installation (unlike fibreglass).

Processing for insulation:

1. Scouring: Raw greasy wool must be washed to remove lanolin, dirt, and vegetable matter. NZ has existing wool scouring capacity — Cavalier Bremworth’s Awatoto plant near Napier and other facilities.⁵⁰ Scouring uses hot water and detergent; the hot water can be heated electrically, and detergent stocks will need to be managed. When commercial detergent stocks are exhausted, soap from tallow is a locally producible alternative (Doc #36), though tallow soap requires its own dependency chain: animal fat (from meat processing), lye (sodium hydroxide, produced by reacting soda ash or wood ash with slaked lime), and processing equipment. Tallow soap is less effective at removing lanolin than commercial scour detergents, so throughput per scour cycle is lower and water consumption is higher.⁵¹ Lanolin recovered from scouring is itself a valuable resource (leather treatment, skin care, lubrication).
2. Treatment: Insulation wool is typically treated with boron compounds (borax or boric acid) to provide resistance to insects, mould, and fire.⁵² NZ does not produce boron compounds — they are imported, primarily from Turkey and the US. The full dependency chain for treated wool insulation is: boron ore (imported) → borax or boric acid (imported, processed) → application to scoured wool at 5–10% by weight. Existing NZ stocks should be allocated to insulation production as a priority, but total boron compound inventory in NZ is unknown and requires immediate audit. If boron stocks are exhausted, untreated wool can still be used as insulation but with significantly reduced durability — untreated wool is vulnerable to moth and carpet beetle damage (which can degrade the insulation layer within 2–5 years in poorly ventilated ceiling spaces) and has reduced fire resistance. Alternative treatments — diatomaceous earth, concentrated salt solutions — provide partial pest resistance but are substantially less effective than boron and do not provide fire retardancy.
3. Forming: Wool can be used as loose-fill (blown or hand-placed into ceiling cavities) or formed into batts (semi-rigid panels held together by mechanical needling or a light binding agent). Loose-fill requires less processing and is suitable for ceiling cavities. Batts are preferable for underfloor and wall cavities where the insulation must stay in position.

Production scale: NZ’s wool clip, even reduced by nuclear winter effects on sheep farming (Doc #74 estimates a 30–60% reduction in livestock numbers), would still produce approximately 50,000–90,000 tonnes of greasy wool per year. After scouring (which removes approximately 40–50% of the weight as grease, dirt, and moisture), clean wool yield is approximately 25,000–50,000 tonnes.⁵³ Commercial wool batt insulation products (e.g., Terra Lana, Woolhome) are installed at approximately 14–20 kg/m³ declared density; at a ceiling depth of 100–120 mm, this implies approximately 1.5–2.5 kg of clean wool per square metre of ceiling.⁵⁴ Loose-fill applications run higher — perhaps 20–30 kg/m³ installed — due to settlement allowance, but still under 4 kg/m². For an average ceiling of 100 m², a typical house requires approximately 150–400 kg of clean wool for ceiling insulation (not 1,000–1,500 kg as stated in the Economic Justification section — that figure requires verification against manufacturer specifications and should be treated with caution until confirmed). At 150–400 kg per house, NZ’s annual clean wool production of 25,000–50,000 tonnes could in principle supply ceiling insulation for 60,000–330,000 houses per year. Over 3–5 years, this is sufficient to cover the highest-priority housing stock. Note: The wool quantity per house should be verified against NZ commercial product data before committing to programme supply estimates.

Honest limitation: Wool competes with textile production (Doc #36). Under recovery conditions, NZ needs wool for both insulation and clothing. However, insulation uses lower-grade wool (daggy, short-staple, and contaminated fleeces that are unsuitable for textile processing), so the competition is less direct than it might appear. A grading and allocation system should direct textile-grade wool to clothing production and lower grades to insulation.

5.2 Straw bale insulation

Straw — the dried stems of cereal crops after grain harvest — is an excellent insulation material with a long history of use in construction. NZ’s cereal cropping (approximately 50,000–60,000 hectares of wheat and barley under normal conditions, concentrated in Canterbury and the Wairarapa) produces straw as a byproduct.⁵⁵

Properties: Straw bale walls have a thermal resistance of approximately R-5 to R-7 for a standard bale thickness (450 mm), comparable to well-insulated modern wall construction.⁵⁶ This is excellent performance for a waste material.

Applications: - New construction: Straw bale walls are a viable construction method for new buildings under recovery conditions. The technique involves stacking bales within or against a timber frame, then rendering both sides with lime plaster or clay plaster. The resulting wall is well-insulated, fire-resistant (the compressed straw with plaster render does not burn readily), and structurally adequate for single-storey buildings.⁵⁷ - Retrofit: Straw bales can be stacked against the exterior of existing buildings to add insulation to poorly insulated walls. This changes the building’s external appearance, adds approximately 500 mm to the wall thickness (affecting window reveals, door access, and site boundaries), and requires a new weatherproof render — a multi-day task per wall face involving lime mixing, application, and curing. It is feasible for buildings with adequate eaves or where a new roof overhang can be added, but is a substantial undertaking per building.

Performance gap vs. manufactured insulation: Straw bales achieve R-5 to R-7 at 450 mm thickness, which is excellent — but this is at nearly four times the thickness of wool or fibreglass batts achieving similar R-values (100–120 mm). This makes straw bales impractical for retrofit into existing wall cavities (which are typically 90–100 mm deep in NZ timber-framed houses). Straw is best suited to new construction or exterior over-cladding, not drop-in replacement for manufactured insulation in existing buildings.

Limitations: - Straw must be dry (below 20% moisture content) to avoid mould and decomposition. In NZ’s humid climate, moisture management is critical — straw bale walls must be protected from rain during construction and must be rendered with a breathable plaster that allows moisture to escape. - Straw supply is limited to cereal-cropping regions. Canterbury is the primary source. Transport to the North Island adds cost and fuel consumption. - Under nuclear winter conditions, cereal cropping area and yield both decline (Doc #75), reducing straw availability. This is a real constraint.

5.3 Sawdust and wood shavings

NZ’s sawmills produce large volumes of sawdust and shavings as a byproduct of timber milling. Under normal conditions, much of this material is used for animal bedding, horticultural mulch, or burned for energy. Under recovery conditions, sawdust becomes a valuable insulation material.

Properties: Loose-fill sawdust and shavings provide thermal insulation with a conductivity of approximately 0.06–0.08 W/m·K — roughly twice the conductivity of wool or fibreglass, meaning approximately twice the thickness is needed for equivalent insulation performance.⁵⁸ This is a meaningful performance gap, but sawdust is abundantly available and essentially free.

Application: Sawdust is best suited for ceiling cavities, where it can be poured or blown in to a depth of 200–400 mm. For a typical NZ house with a 100 m² ceiling, this requires approximately 2–4 cubic metres of sawdust — easily sourced from any local sawmill.

Limitations: - Fire risk: Dry sawdust is flammable. It should not be in contact with heat sources (downlights, chimneys, electrical wiring that may overheat). Downlights are a particular hazard in NZ houses — they must be fitted with protective enclosures (can be fabricated from sheet metal) before sawdust is placed in the ceiling cavity. Boric acid treatment reduces fire risk but requires boron compounds. - Settling: Loose-fill sawdust settles over time (approximately 10–20% settlement), reducing effective thickness. Overfill initially to compensate, and top up as needed. - Moisture: Sawdust absorbs moisture readily. In poorly ventilated ceiling spaces, moisture accumulation can cause mould growth and timber decay. Adequate ventilation of the roof space is essential. - Pests: Untreated sawdust may attract insects. Boric acid treatment mitigates this.

5.4 Recycled paper and cardboard (cellulose insulation)

NZ has substantial stocks of paper and cardboard — in warehouses, retail premises, recycling depots, and households. Under recovery conditions, much of this material has no other use (printing and packaging demand drops with the cessation of normal commerce).

Properties: Shredded and treated paper (cellulose insulation) has a thermal conductivity of approximately 0.035–0.040 W/m·K — comparable to wool and fibreglass.⁵⁹ It is an established commercial insulation product in NZ and internationally.

Processing: Commercial cellulose insulation is produced by shredding newspaper, treating it with boron compounds (for fire resistance and pest deterrence), and blowing it into building cavities with a machine. Under recovery conditions:

• Shredding can be done with existing commercial shredders or improvised mechanical systems.
• Boron treatment is important for fire resistance — untreated paper insulation is a significant fire hazard and should not be used without treatment.
• Installation requires a blowing machine for wall cavities (NZ insulation contractors operate these machines; they are electrically powered and mechanically robust but require periodic replacement of seals and hoses). Ceiling cavities can be hand-filled with loose shredded paper, though blown installation is faster and more uniform.

Limitation: Recycled paper is a finite stock, not a renewable supply. Once existing stocks are consumed, no more is available until NZ’s paper production (Doc #29) is operating at scale. Prioritise paper insulation for situations where its superior performance (compared to sawdust) or ease of installation justifies drawing down the stock.

5.5 Earth and thermal mass

Earth does not insulate in the same way as fibrous materials — its thermal conductivity is high (approximately 1.0–1.5 W/m·K for dry earth).⁶⁰ However, earth has significant thermal mass: it absorbs heat slowly and releases it slowly, moderating temperature swings. Rammed earth walls, earth-sheltered construction, and earth banking against existing buildings all exploit thermal mass to maintain more stable indoor temperatures.

Performance gap: Earth is not a substitute for fibrous insulation. Its thermal conductivity (0.5–1.5 W/m·K) is 10–40 times worse than wool or fibreglass (0.035–0.040 W/m·K). Its value lies in thermal mass — moderating temperature swings over a 24-hour cycle — not in preventing heat transfer. A rammed earth wall without additional insulation will still lose heat rapidly in sustained cold conditions.

Application to existing NZ houses: Banking earth against the lower walls and foundation of an existing house reduces heat loss through the lower wall area and provides thermal mass buffering. This is a labour-intensive intervention (estimated 4–10 person-hours per house, depending on perimeter length and soil access) requiring no manufactured materials but needing competent drainage management (earth banking must not direct water toward the foundation) and vermin exclusion.

New construction: Rammed earth construction is a viable method for new buildings under recovery conditions (see also Doc #97, Section 6.5). Rammed earth walls stabilised with a small amount of cement (4–8%) provide excellent thermal mass, moderate insulation, and structural adequacy for single-storey buildings. In combination with ceiling insulation (wool, sawdust, or cellulose), rammed earth buildings can perform well under nuclear winter conditions. Traditional Māori building knowledge includes techniques for constructing warm, dry, and wind-resistant dwellings using earth and local plant materials. Raupō (bulrush) and other plant materials were used for wall and roof cladding in traditional whare, providing both weather protection and insulation.⁶¹ The underlying principles — using locally available plant materials for thermal protection, orientation for solar gain, and community-scale construction — are applicable to recovery-period building.

5.6 Material comparison

Material	Thermal conductivity (W/m·K)	Thickness for R-2.9 ceiling (mm)	NZ availability	Processing required
Wool batts/loose-fill	0.035–0.040	100–120	Abundant (sheep flock)	Scouring, treatment
Cellulose (recycled paper)	0.035–0.040	100–120	Moderate (finite stock)	Shredding, boron treatment
Sawdust/shavings	0.060–0.080	175–230	Abundant (sawmills)	Collection, possible treatment
Straw bales (450mm)	~0.060 (bale)	450 (standard bale)	Moderate (cropping regions)	Baling, dry storage
Fibreglass (existing stocks)	0.035–0.045	100–130	Finite (no NZ production)	None (manufactured product)

Note: R-2.9 is the current NZ Building Code minimum for ceiling insulation in most climate zones.⁶² Under nuclear winter conditions, higher R-values would be desirable where materials permit.

---

6. DRAUGHT-PROOFING AND WINDOW IMPROVEMENTS

6.1 Draught-proofing: the highest-return intervention

Sealing air leaks is the cheapest and most effective single intervention for improving the thermal performance of NZ houses. In many older NZ houses, air leakage accounts for 15–25% of total heat loss — and this fraction increases in windy conditions, which are common across much of NZ.⁶³

Common draught pathways in NZ houses:

• Gaps around windows and doors (especially older wooden-framed windows and doors that have warped or shrunk)
• Gaps between floorboards (suspended timber floors)
• Gaps around service penetrations (plumbing, electrical, telecommunications)
• Open chimneys and fireplaces (when not in use)
• Gaps between wall cladding and framing
• Ceiling penetrations (downlights, access hatches, ceiling fans)
• Exhaust fans without dampers

Draught-proofing methods:

• Adhesive foam strip: The standard modern product for sealing around doors and windows. NZ has stocks of this product at hardware retailers. When stocks are exhausted, wool felt strips, fabric strips, or rubber offcuts can substitute. The performance gap is real: adhesive foam compresses evenly and maintains a consistent seal across the door frame; hand-cut fabric or felt strips are harder to fit uniformly, may shift over time, and provide lower total air-tightness — expect perhaps 50–70% of the draught reduction achieved with properly fitted foam strip. Rubber offcuts (from gaskets, vehicle seals, or horticultural tubing) perform closer to foam strip where a good fit can be achieved.
• Sealant and filler: Gaps in walls, floors, and around penetrations can be sealed with caulking, putty, or improvised fillers (clay mixed with fibrous material, paper pulp paste, or plaster). Expanding foam sealant is effective but is an imported product with finite stocks.
• Draught stoppers: Fabric tubes filled with sand, rice, or sawdust placed along the base of doors. These can be sewn or tied from any available fabric and filled in minutes.
• Chimney balloons/blockers: Open fireplaces that are not in use should be sealed with a removable blocker — an inflated bag, a board cut to fit the fireplace opening, or a tightly packed wool plug. Open chimneys can account for 5–10% of total house heat loss.⁶⁴
• Floor sealing: Gaps between floorboards in older NZ houses can be filled with papier-mache (shredded paper mixed with PVA glue or flour paste), timber strips, or rope caulking. Covering the floor with carpet, rugs, or any insulating material also reduces air leakage and floor-surface heat loss.

Cost-benefit ratio: A thorough draught-proofing of a typical older NZ house takes approximately 2–6 person-hours and uses minimal materials. The reduction in heat loss is typically 10–20%, immediately and permanently.⁶⁵ No other single intervention in NZ housing provides comparable thermal improvement per person-hour invested. Draught-proofing should be the first priority in every house before any insulation is installed.

6.2 Window improvements

Windows are the weakest thermal element in almost every NZ house. Single-glazed aluminium-framed windows — standard in NZ construction from the 1960s to the 2000s — have a thermal resistance of approximately R-0.15, compared to R-2.0 or more for an insulated wall.⁶⁶ Windows are thermal holes.

Secondary glazing: Adding a second layer of glazing inside the existing window frame dramatically improves thermal performance. The air gap between the two panes (ideally 12–20 mm) acts as insulation.

• DIY secondary glazing with plastic film: A sheet of clear plastic (polycarbonate, acrylic, or heavy-gauge polyethylene film) fixed to the interior window frame with magnetic strips, clips, or a timber bead creates an effective secondary glazing unit. This is the approach promoted by community groups in NZ and the UK, and it works — studies show reductions in window heat loss of 40–60%.⁶⁷ Dependency note: Polycarbonate, acrylic, and polyethylene sheeting are all imported petrochemical products. NZ has no domestic production pathway. Under recovery conditions, existing stocks (from hardware retailers, greenhouse suppliers, and commercial stocks) are finite and should be prioritised for the highest-value applications. As plastic stocks deplete, recovered glass becomes the primary secondary glazing material.
• Recovered glass: Under recovery conditions, glass from non-essential sources (display cases, picture frames, damaged vehicles, commercial shop fronts) can be cut and fitted as permanent secondary glazing. This requires glass-cutting skills and careful fitting but produces a durable, long-lasting improvement. Glass secondary glazing is heavier and more fragile than plastic alternatives but is available domestically from salvage and does not deplete in the way that imported plastic sheeting does. It is the preferred long-term material.
• Performance: Secondary glazing improves thermal resistance from approximately R-0.15 (single glazing) to R-0.30–0.40 (comparable to double glazing).⁶⁸ This roughly halves window heat loss.

Thermal curtains: Heavy curtains with a close fit to the window frame and wall significantly reduce heat loss — by approximately 40–60% for a well-fitted thermal curtain with a pelmet (valance) at the top.⁶⁹

• Materials: Heavy wool fabric, wool blankets, or layered cotton/wool composites. NZ can produce all of these from domestic resources.
• Design: The curtain must be close-fitting to the wall at the sides (ideally with magnetic strips or press studs to seal the edges) and have a pelmet at the top to prevent warm air flowing up behind the curtain and losing heat to the cold window. A curtain that hangs free from the wall is much less effective.
• Operation: Open curtains during sunny periods (especially north-facing windows) to admit solar gain. Close curtains as soon as the sun is off the window, and keep them closed overnight.

Honest performance gap: Secondary glazing and thermal curtains are meaningful improvements but they do not make a single-glazed window perform like a modern triple-glazed unit. The improvement is from very poor to moderate — but in a house where windows are responsible for 15–20% of heat loss, halving that loss is significant.

---

7. RETROFIT STRATEGY AND PRIORITISATION

7.1 Priority order of interventions

For any individual house, the priority order of thermal improvement is:⁷⁰

1. Draught-proofing — highest return, lowest cost, immediate effect
2. Ceiling insulation — highest heat loss pathway, easiest to access and retrofit in NZ houses
3. Underfloor insulation — significant heat loss pathway, accessible in most NZ houses (suspended timber floors with crawl space)
4. Thermal curtains / secondary glazing — moderate return, moderate effort
5. Wall insulation — significant heat loss pathway but hardest to retrofit (requires either removing interior or exterior cladding, or injecting insulation into the wall cavity)

7.2 Priority targeting: who gets insulated first

Not all houses can be insulated at once. The programme must prioritise based on two factors: vulnerability of occupants and severity of thermal performance.

Tier 1 (immediate — first 6 months): - Houses with no ceiling insulation occupied by elderly persons living alone or with a partner - Houses with no ceiling insulation occupied by families with children under 5 - Houses with no ceiling insulation used as community housing or social housing

Tier 2 (first year): - Houses with partial or degraded ceiling insulation occupied by any of the above groups - Houses with no underfloor insulation in the South Island (where floor heat loss is most severe under nuclear winter) - Community facilities used as heated gathering spaces (marae, halls, churches)

Tier 3 (years 1–3): - All remaining houses with substandard insulation - Wall insulation where feasible - Secondary glazing programme

7.3 Implementation structure

Assessment teams: Small teams (2 people) trained to quickly assess a house’s insulation status and identify the highest-return interventions. A competent assessor can evaluate a house in 30–60 minutes by inspecting the ceiling cavity, underfloor space, window type, and obvious draught sources.

Installation teams: Teams of 2–4 workers trained in insulation installation. Ceiling insulation installation is not highly skilled work — the main requirements are safety awareness (ceiling access, working in confined spaces, awareness of electrical hazards), material handling, and knowledge of coverage requirements and critical details (maintaining ventilation gaps, keeping insulation clear of downlights and recessed fixtures, ensuring coverage to edges and around obstructions).

Coordination: Regional coordination through district councils, Civil Defence, or dedicated housing units. The existing Warmer Kiwi Homes programme structure (administered through EECA — the Energy Efficiency and Conservation Authority) provides a model for programme delivery, assessment protocols, and quality standards.⁷¹ In areas with significant Māori populations, the programme should work with and through existing whānau, hapū, and iwi structures. Kaupapa (purpose-driven) working bees are an established practice in Māori communities and provide a tested organisational framework for collective housing improvement. Communities with strong social organisation and existing gathering infrastructure will implement the retrofit programme faster and more effectively than those that must build these structures from scratch.

Quality control: Insulation installed poorly is much less effective than insulation installed correctly. Common errors: insufficient thickness, gaps at edges and around obstructions, compression of insulation (which reduces its effectiveness), failure to seal around penetrations, and blocking of required ventilation. A visual inspection by a second person after installation — checking coverage, thickness, edge sealing, and clearance around heat sources — catches most of these errors.

---

8. COMMUNITY HEATING

8.1 The principle

Heating many individual houses is less efficient than heating shared spaces where people gather during the coldest periods. Community heated spaces — marae, churches, community halls, schools, libraries — can serve as warming centres for the most vulnerable, reducing the total heating demand on NZ’s energy systems and providing social connection during a period of severe stress.

8.2 NZ’s existing community infrastructure

NZ has a dense network of community facilities:

• Marae: Approximately 700+ marae throughout NZ, many with large meeting houses (wharenui) and dining halls (wharekai) that can accommodate dozens to hundreds of people.⁷² Marae are purpose-built community gathering places with kitchen facilities and, in many cases, overnight accommodation capability. They have an established role in emergency response — marae have served as evacuation centres during floods, earthquakes, and other events. Marae-based community heating during nuclear winter is a natural extension of this role.
• Churches and church halls: Thousands of churches of all denominations throughout NZ, many with associated halls and kitchen facilities.
• Community halls: Most NZ towns and many rural areas have public or community-owned halls.
• Schools: NZ has approximately 2,500 schools (state and state-integrated), most with halls and heated classrooms.⁷³ During school holidays or in the evenings, these spaces can serve as community warming centres.
• Libraries: Public libraries in most towns provide heated spaces and are already community gathering points.

8.3 Operating community heated spaces

Heating: A single large space can be heated efficiently with a wood burner, heat pump, or electric heating. The heating energy per person is much lower than heating individual houses — a hall serving 50 people might use 10–25 kW of heating (depending on hall size, insulation, and outdoor temperature), whereas those 50 people in 25–35 separate houses would collectively require 50–150 kW.⁷⁴ The ratio is approximate but the underlying physics — that heat loss scales with building envelope area, not with occupant count — means that consolidating people into fewer, larger spaces always reduces aggregate heating demand.

Schedule: Community heated spaces need not operate 24 hours a day. A daytime schedule (8am–8pm) allows the most vulnerable to spend the coldest waking hours in a warm environment, returning home to sleep (where bedding and hot water bottles provide adequate warmth even in cool houses). Overnight operation may be needed for the most vulnerable during extreme cold periods.

Services: Community heated spaces can combine warming with other essential services — communal meals (reducing individual heating for cooking), health checks, information distribution, social activities, and childcare. This multi-function approach maximises the return on the heating energy invested.

8.4 Insulating community buildings

Community buildings targeted for use as heated spaces should be among the first buildings insulated. The return on investment is high — every improvement in the building envelope reduces the heating energy needed to serve dozens or hundreds of people.

---

9. EXISTING NZ PROGRAMMES AS A MODEL

NZ has already implemented large-scale insulation retrofit programmes that provide a direct operational model for the recovery programme:

9.1 Warmer Kiwi Homes (and predecessor programmes)

The Warmer Kiwi Homes programme (administered by EECA) provides grants for ceiling insulation, underfloor insulation, and heating in low-income households. Its predecessor, Warm Up New Zealand: Heat Smart, insulated approximately 300,000 homes between 2009 and 2016.⁷⁵

What this programme established: - Assessment protocols for determining insulation need - Quality standards for installation - Training and accreditation for installation contractors - Logistics for material supply and distribution - Targeting frameworks for reaching the most vulnerable households - Monitoring and evaluation methods

Under recovery conditions: The Warmer Kiwi Homes administrative structure, contractor networks, and assessment protocols provide a ready-made framework for rapid scale-up. Many of the contractors who performed insulation work under the programme retain the skills and knowledge. EECA’s institutional knowledge of programme delivery, problem houses, and regional variation is valuable.

9.2 Healthy Homes Standards

The Healthy Homes Standards (2019) set minimum standards for insulation, heating, ventilation, moisture, and draught stopping in rental properties.⁷⁶ These standards provide a practical benchmark for retrofit targets:

• Ceiling insulation to at least R-2.9 (or existing insulation topped up if below this level)
• Underfloor insulation to at least R-1.3
• A fixed heating device capable of achieving 18°C in the main living room
• Adequate ventilation (extractor fans in kitchen and bathroom)
• Draught stopping of unnecessary gaps and openings

These standards are a reasonable minimum target for the recovery retrofit programme, adapted as necessary for material availability.

---

10. CRITICAL UNCERTAINTIES

Uncertainty	Range	Impact
Severity of nuclear winter cooling for NZ	5–8°C average	Directly determines heating demand increase and health impact
Duration of peak nuclear winter	2–5 years at full severity	Determines how many winters the retrofit must cover
Condition of NZ’s existing housing insulation	Highly variable; incompletely surveyed	Determines actual retrofit requirement — may be better or worse than assumed
Wool supply under reduced sheep flock	50,000–90,000 tonnes greasy wool/year (estimate)	Determines insulation material availability; competition with textile use
Boron compound stocks for insulation treatment	Unknown; requires inventory	Determines whether treated insulation can be produced at scale or whether untreated alternatives must be used
Heat pump fleet longevity	5–15 years depending on refrigerant and component failure rates	Determines how long NZ’s most efficient heating technology remains available
Grid capacity for increased winter heating load	Peak demand 8,000–10,000 MW vs. current 7,000 MW capacity	Determines whether electric heating can serve all of NZ or whether load shedding is required
Labour availability for retrofit	Competes with agriculture, infrastructure, manufacturing	Determines speed of programme implementation
Urban air quality from increased wood burning	Depends on concentration, meteorological conditions	Determines whether wood heating creates a secondary health problem

---

11. CROSS-REFERENCES

Document	Relationship
Doc #1 — National Emergency Stockpile Strategy	Insulation material stocks; hardware supplies; allocation framework
Doc #156 — Skills Census	Housing stock data; builder workforce; wool processing capacity
Doc #29 — Paper and Ink Production	Paper stocks available for cellulose insulation
Doc #36 — Clothing and Footwear	Wool allocation between insulation and textile use
Doc #56 — Wood Gasification	Complementary wood energy technology; shared forestry resource
Doc #67 — Transpower Grid Operations	Grid capacity for electric heating; load management under increased demand
Doc #69 — Transformer Maintenance	Grid reliability for heat pump and electric heating supply
Doc #74 — Pastoral Farming Under Nuclear Winter	Wool supply under reduced sheep flock; wool grade allocation
Doc #75 — Cropping Under Nuclear Winter	Straw supply from cereal cropping
Doc #97 — Cement and Concrete	Rammed earth and cement-stabilised construction for new buildings
Doc #102 — Charcoal Production	Shared forestry resource; firewood supply chain
Doc #116 — Pharmaceutical Rationing	Health system strain from cold-related illness
Doc #[verify] — Surgical Capability	Hospital demand from cold-related complications — document number requires verification against catalog
Doc #122 — Mental Health	Community heated spaces as social support infrastructure
Doc #145 — Emergency Governance	Legal framework for housing standards and material allocation
Doc #[verify] — Workforce Reallocation	Labour allocation to insulation retrofit — document number requires verification against catalog
Doc #157 — Trade Training	Insulation installer training programme
Doc #160 — Heritage Skills	Traditional building and insulation knowledge

---

---

1. Stats NZ, “Dwelling and Household Estimates,” https://www.stats.govt.nz/ — NZ has approximately 1.8–1.9 million private dwellings. The exact number at the time of the event depends on the pace of construction. The figure used in this document (1.8 million) is approximate.↩︎

2. The “cold houses” problem in NZ is extensively documented. Key references: Howden-Chapman, P. et al., “Effect of insulating existing houses on health inequality: cluster randomised study in the community,” BMJ, 334(7591), 2007, pp. 460–464; BRANZ, “Study Report SR297: NZ Housing Condition Survey,” various editions. NZ’s housing thermal performance is consistently rated as poor by international comparison.↩︎

3. Indoor temperature estimates under nuclear winter are derived by applying the estimated cooling (5–8°C, from nuclear winter climate models) to known NZ indoor temperature data (BRANZ housing surveys). The relationship between outdoor and indoor temperature in NZ houses is documented in BRANZ HEEP (Household Energy End-use Project) data. This is an extrapolation, not a modeled prediction, and actual outcomes will vary significantly by house type, orientation, and occupant behaviour.↩︎

4. NZ wool production: Ministry for Primary Industries, Situation and Outlook for Primary Industries (SOPI) reports. https://www.mpi.govt.nz/ — NZ produces approximately 120,000–140,000 tonnes of greasy wool per year (fluctuating with sheep numbers and seasonal conditions). Approximately 80–85% is crossbred (strong) wool. Under nuclear winter conditions with reduced sheep numbers (Doc #99), wool production will decline but remain substantial.↩︎

5. NZ plantation forestry: Ministry for Primary Industries, National Exotic Forest Description (NEFD). https://www.mpi.govt.nz/ — Approximately 1.7 million hectares, predominantly radiata pine, with annual roundwood production of approximately 30–35 million cubic metres.↩︎

6. NZ electricity generation is approximately 85% renewable (hydro, geothermal, wind) — MBIE, Energy in New Zealand. https://www.mbie.govt.nz/building-and-energy/energy-and-n... — The grid does not depend on imported fuel for generation. Firewood supply is a small fraction of NZ’s annual forest growth (see Section 4.3).↩︎

7. Insulation installation labour: based on NZ insulation industry experience and Warmer Kiwi Homes programme data. Ceiling insulation retrofit for an average-sized NZ house (100–120 m² ceiling area) takes an experienced two-person team approximately 2–4 hours, depending on ceiling access, obstructions, and existing conditions. Underfloor insulation takes longer due to working conditions (crawl spaces, limited access, fastening to joists). These are estimates; actual times vary significantly with house design.↩︎

8. Cost of cold housing to the NZ health system: estimates vary. The NZ Green Building Council cited approximately $145 million per year in direct health costs attributable to cold, damp housing. Preval, N. et al., “Evaluating energy, health and carbon co-benefits from improved domestic space heating,” Energy Policy, 38(8), 2010, pp. 3965–3972, estimated substantial health savings from insulation. The $50–150 million range reflects the uncertainty across different estimation methods.↩︎

9. Excess winter mortality in NZ: Davie, G. et al., “Excess winter mortality in New Zealand,” NZ Medical Journal, 120(1259), 2007. Approximately 1,600 excess deaths per winter is a commonly cited figure, though the number varies year to year with winter severity and influenza prevalence. NZ’s excess winter mortality rate (as a percentage of non-winter deaths) is comparable to countries with much colder climates but well-insulated housing, suggesting that housing quality — not climate — is the primary driver.↩︎

10. Insulation installation labour: based on NZ insulation industry experience and Warmer Kiwi Homes programme data. Ceiling insulation retrofit for an average-sized NZ house (100–120 m² ceiling area) takes an experienced two-person team approximately 2–4 hours, depending on ceiling access, obstructions, and existing conditions. Underfloor insulation takes longer due to working conditions (crawl spaces, limited access, fastening to joists). These are estimates; actual times vary significantly with house design.↩︎

11. Heating energy reduction from insulation: BRANZ Study Report SR297 and the HEEP project documented typical energy savings of 30–50% from ceiling and underfloor insulation in previously uninsulated NZ houses. The actual saving depends on house type, climate zone, and occupant heating behaviour. Some studies show smaller savings because occupants “take back” some of the benefit as higher indoor temperatures rather than lower energy use — this is a desirable outcome from a health perspective.↩︎

12. Grimes, A. et al., “Cost Benefit Analysis of the Warm Up New Zealand: Heat Smart Programme,” Motu Economic and Public Policy Research, 2012. The estimated benefit-cost ratio of approximately 3.9:1 included health benefits, energy savings, and reduced mortality. Benefits were disproportionately concentrated in houses with the worst pre-retrofit conditions.↩︎

13. Stats NZ, “Dwelling and Household Estimates,” https://www.stats.govt.nz/ — NZ has approximately 1.8–1.9 million private dwellings. The exact number at the time of the event depends on the pace of construction. The figure used in this document (1.8 million) is approximate.↩︎

14. NZ Building Code insulation history: NZS 4218:1977 was the first NZ standard requiring insulation in new residential buildings. Houses built before this date generally have no insulation unless subsequently retrofitted. Approximately 800,000 NZ dwellings were built before 1978. See: BRANZ housing condition surveys; NZ Building Code history.↩︎

15. Insulation standards 1978–2000: NZS 4218:1977 and its 1996 revision required ceiling insulation (R-1.9 in most zones — approximately half the current minimum) and did not require underfloor or wall insulation in most zones. The 2000 and subsequent revisions progressively increased requirements. Houses built between 1978 and 2000 typically have some ceiling insulation but may lack underfloor and wall insulation. See: BRANZ Study Reports on NZ housing thermal performance.↩︎

16. BRANZ housing research: The Household Energy End-use Project (HEEP), conducted by BRANZ over 1997–2005, is the most comprehensive study of NZ housing energy use and indoor temperatures. Key publications: Isaacs, N. et al., “Energy Use in New Zealand Households: Report on the Year 10 Analysis for the Household Energy End-use Project (HEEP),” BRANZ Study Report SR155, 2006. Also: BRANZ Housing Condition Survey reports (various years).↩︎

17. WHO indoor temperature recommendations: WHO Housing and Health Guidelines, 2018, recommend a minimum indoor temperature of 18°C to protect health. Many international comfort standards specify 20–22°C for occupied rooms. NZ’s median winter living room temperature of approximately 16°C (BRANZ HEEP data) is below the WHO minimum.↩︎

18. Heat loss pathways in NZ houses: proportions are approximate and vary significantly with house design, age, and condition. The figures cited are broadly consistent with BRANZ research and NZ building science literature. See: Isaacs et al. (note 14); BRANZ bulletins on residential thermal performance.↩︎

19. Air tightness of NZ houses: Reported air tightness values from NZ studies show that older NZ houses are very leaky. McNeil, S. et al., “Airtightness of New Zealand houses,” BRANZ Conference Paper, 2012, reported median ACH50 values of approximately 8–12 for newer houses and 15–25 for older houses, compared to international cold-climate practice of 3–5 ACH50. Air leakage is a major contributor to poor thermal performance.↩︎

20. Excess winter mortality in NZ: Davie, G. et al., “Excess winter mortality in New Zealand,” NZ Medical Journal, 120(1259), 2007. Approximately 1,600 excess deaths per winter is a commonly cited figure, though the number varies year to year with winter severity and influenza prevalence. NZ’s excess winter mortality rate (as a percentage of non-winter deaths) is comparable to countries with much colder climates but well-insulated housing, suggesting that housing quality — not climate — is the primary driver.↩︎

21. Housing, Insulation and Health Study: Howden-Chapman, P. et al. (note 2). This landmark cluster-randomised study demonstrated that insulating NZ houses reduced self-reported cold symptoms, GP visits, and days off school and work. It provided robust evidence for the health benefits of insulation that underpinned subsequent government programmes.↩︎

22. Child health and cold housing: Baker, M. et al., “Household crowding a major risk factor for epidemic meningococcal disease in Auckland children,” Pediatric Infectious Disease Journal, 19(10), 2000; Craig, E. et al., “Monitoring the Health of New Zealand Children and Young People,” NZ Child and Youth Epidemiology Service, University of Otago. NZ has high rates of child hospitalisation for respiratory illness by international comparison, and cold, damp, overcrowded housing is a significant contributing factor.↩︎

23. Housing inequality: Stats NZ Census data shows significant disparities in housing quality by ethnicity and income. Maori and Pasifika households are more likely to live in rental accommodation, older housing stock, and overcrowded conditions. The 2018 Census reported that approximately 15% of Maori households were crowded, compared to 6% of NZ European households. See: Stats NZ, “Housing in Aotearoa: 2020.” https://www.stats.govt.nz/↩︎

24. Nuclear winter climate estimates for NZ: Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007; Coupe, J. et al., “Nuclear Nino response observed in simulations of nuclear war scenarios,” Communications Earth & Environment, 2021. The 5–8°C cooling range for NZ reflects Recoverable Foundation’s assessment based on these and related models — the range accounts for uncertainty in NZ-specific effects within global nuclear winter scenarios.↩︎

25. NIWA Climate Summaries: National Institute of Water and Atmospheric Research (NIWA), “Climate Summaries.” https://niwa.co.nz/climate — Temperature data for NZ stations. The figures in the table are approximate long-term averages for representative urban stations.↩︎

26. Indoor temperature in unheated buildings: the 2–5°C uplift above average outdoor temperature in an unheated building is a standard rule of thumb in building physics, arising from incidental heat gains (occupant metabolic heat, approximately 80–120 W per person; cooking; lighting; solar gain through windows). The actual uplift depends on building mass, occupancy, and orientation. See: CIBSE Guide A, “Environmental Design”; building physics textbooks.↩︎

27. Heating energy increase under nuclear winter: the estimate of 2–3× normal NZ winter heating energy is derived from the heating degree-day (HDD) method. NZ’s major cities have base-18°C HDDs under normal conditions of approximately: Auckland 650, Wellington 1,250, Christchurch 1,700, Dunedin 1,900, Invercargill 2,100 (approximate annual totals from NIWA climate data). A uniform 5–8°C cooling increases effective HDDs by 5–8°C × 365 days = 1,825–2,920 HDD. This represents a 90–450% increase depending on location — the highest proportional increase in the warmest cities (Auckland) and the lowest in already-cold cities (Invercargill). The 2–3× range cited in the text is an approximate central estimate for occupied NZ cities taken as a whole; South Island cities would see proportionally larger increases. See: NIWA Climate Atlas; CIBSE “Degree-Days: Theory and Application” (TM41, 2006) for methodology.↩︎

28. Nuclear winter climate estimates for NZ: Robock, A. et al., “Nuclear winter revisited with a modern climate model and current nuclear arsenals,” Journal of Geophysical Research, 2007; Coupe, J. et al., “Nuclear Nino response observed in simulations of nuclear war scenarios,” Communications Earth & Environment, 2021. The 5–8°C cooling range for NZ reflects Recoverable Foundation’s assessment based on these and related models — the range accounts for uncertainty in NZ-specific effects within global nuclear winter scenarios.↩︎

29. Temperature-health relationships: Collins, K.J., “Low indoor temperatures and morbidity in the elderly,” Age and Ageing, 15(4), 1986, pp. 212–220; Jevons, R. et al., “Minimum indoor temperature thresholds for health in winter,” Journal of Epidemiology and Community Health, 2016. The temperature thresholds cited (16°C, 12°C, 9°C) are approximate and vary by individual health status, activity level, and clothing.↩︎

30. NZ population aged 65+: Stats NZ population estimates. https://www.stats.govt.nz/ — Approximately 850,000 people aged 65 and over as of 2024, projected to increase. Under recovery conditions, the older population is particularly vulnerable due to pre-existing health conditions and thermoregulatory decline with age.↩︎

31. NZ children under 5: Stats NZ population estimates. Approximately 290,000–310,000 children aged 0–4. This group is particularly vulnerable to cold-related respiratory illness.↩︎

32. Housing inequality: Stats NZ Census data shows significant disparities in housing quality by ethnicity and income. Maori and Pasifika households are more likely to live in rental accommodation, older housing stock, and overcrowded conditions. The 2018 Census reported that approximately 15% of Maori households were crowded, compared to 6% of NZ European households. See: Stats NZ, “Housing in Aotearoa: 2020.” https://www.stats.govt.nz/↩︎

33. Excess winter mortality in NZ: Davie, G. et al., “Excess winter mortality in New Zealand,” NZ Medical Journal, 120(1259), 2007. Approximately 1,600 excess deaths per winter is a commonly cited figure, though the number varies year to year with winter severity and influenza prevalence. NZ’s excess winter mortality rate (as a percentage of non-winter deaths) is comparable to countries with much colder climates but well-insulated housing, suggesting that housing quality — not climate — is the primary driver.↩︎

34. NZ heat pump installations: EECA (Energy Efficiency and Conservation Authority) data. NZ has experienced rapid growth in heat pump installations since the early 2000s. The estimated installed base of 450,000–500,000 units (approximately one in four dwellings) is based on industry estimates and EECA reporting. The exact figure is uncertain because no central registry exists.↩︎

35. Heat pump COP at low temperatures: Performance data from heat pump manufacturer specifications and independent testing. COP values at various outdoor temperatures are approximate and vary significantly by model, refrigerant type, and installation quality. The general trend — declining COP with declining outdoor temperature — is universal for air-source heat pumps. Modern inverter units with cold-climate ratings perform better at low temperatures than older fixed-speed units. See: BRANZ Study Reports on heat pump performance in NZ conditions.↩︎

36. Heat pump COP at low temperatures: Performance data from heat pump manufacturer specifications and independent testing. COP values at various outdoor temperatures are approximate and vary significantly by model, refrigerant type, and installation quality. The general trend — declining COP with declining outdoor temperature — is universal for air-source heat pumps. Modern inverter units with cold-climate ratings perform better at low temperatures than older fixed-speed units. See: BRANZ Study Reports on heat pump performance in NZ conditions.↩︎

37. Heat pump refrigerant leakage and fleet attrition: Refrigerant leakage rates for residential split-system heat pumps are typically 2–5% of charge per year, though rates vary widely. A system that loses sufficient refrigerant to affect performance typically requires recharging within 5–15 years. Without imported refrigerant stocks, units that develop significant leaks must be retired. The 5–15% annual fleet attrition rate is an estimate; actual attrition depends on the age distribution and maintenance history of the installed fleet. This estimate requires verification from NZ HVAC industry data.↩︎

38. NZ electricity statistics: MBIE, “Energy in New Zealand” (annual publication). https://www.mbie.govt.nz/ — Total generation approximately 42,000–43,000 GWh/year. Residential consumption approximately 12,000–13,000 GWh/year. These are normal-year figures; nuclear winter conditions would alter both generation (reduced hydro inflows are possible) and demand (increased heating).↩︎

39. New Zealand Aluminium Smelter (NZAS) at Tiwai Point: consumes approximately 13% of NZ’s total electricity generation (approximately 570 MW continuous load). Closing the smelter would free this capacity for other uses. The decision to close or continue the smelter is discussed in Doc #109. Under recovery conditions, the economic case for diverting this power to heating and other essential uses is strong.↩︎

40. Wood burner prevalence in NZ: Stats NZ Census data on heating fuel; BRANZ HEEP data. Approximately 30–35% of NZ households use wood as a heating source (wood burner or open fireplace). The prevalence is higher in rural areas and lower in newer urban subdivisions. The estimated 600,000 dwellings with wood heating capacity is derived from these figures.↩︎

41. NZ plantation forestry: Ministry for Primary Industries, National Exotic Forest Description (NEFD). https://www.mpi.govt.nz/ — Approximately 1.7 million hectares, predominantly radiata pine, with annual roundwood production of approximately 30–35 million cubic metres.↩︎

42. Firewood consumption estimate: A typical NZ household with a wood burner as primary heating uses approximately 4–8 cubic metres of firewood per year under normal conditions. Under nuclear winter conditions with a longer and colder heating season, consumption would increase — perhaps 6–10 cubic metres per year per household. At 600,000 wood-heated households, total demand is approximately 3.5–6 million cubic metres per year. This is roughly 10–20% of NZ’s annual forestry production — easily sustainable. These are estimates with significant uncertainty; actual consumption depends on house insulation level, occupant behaviour, and winter severity.↩︎

43. Urban air quality from wood burning: Ministry for the Environment, “NZ’s Environmental Reporting Series: Our Air 2018.” https://environment.govt.nz/ — Wood smoke is the primary source of wintertime PM10 exceedances in many NZ towns. Christchurch, Nelson, Timaru, and Rotorua are among the most affected. Under nuclear winter conditions with increased wood burning and potential temperature inversions (cold, stable air trapping pollutants), air quality would worsen unless offset by improved combustion technology and practice.↩︎

44. Solar radiation reduction under nuclear winter: Robock, A. et al. (note 21) and Coupe, J. et al. (note 21) model global reductions in surface solar radiation of 20–40% at peak nuclear winter severity, with recovery over 5–10 years. NZ, being in the Southern Hemisphere and distant from the main injection zones, experiences a moderated effect. The 10–30% range used here reflects this geographic attenuation, with the lower bound corresponding to later recovery years and the upper bound to peak severity. The actual reduction at any NZ location depends on atmospheric soot transport patterns, which are model-dependent.↩︎

45. NZ wool production: Ministry for Primary Industries, Situation and Outlook for Primary Industries (SOPI) reports. https://www.mpi.govt.nz/ — NZ produces approximately 120,000–140,000 tonnes of greasy wool per year (fluctuating with sheep numbers and seasonal conditions). Approximately 80–85% is crossbred (strong) wool. Under nuclear winter conditions with reduced sheep numbers (Doc #99), wool production will decline but remain substantial.↩︎

46. Wool insulation thermal conductivity: published thermal performance data for commercial wool insulation products (e.g., Terra Lana, Woolhome, Thermafleece). Typical declared thermal conductivity is 0.035–0.040 W/m·K, which is comparable to fibreglass batts and within 10% of the best-performing mineral wool and cellulose products. See: manufacturer product data; BRANZ Appraisal certificates for NZ wool insulation products.↩︎

47. Wool moisture buffering: wool fibre can absorb and desorb moisture vapour (up to approximately 30% of its dry weight) without significant loss of thermal resistance. Fibreglass does not absorb moisture but allows condensation to accumulate in the insulation layer, reducing thermal performance. Wool’s moisture management is a significant practical advantage in NZ’s humid climate. See: Korjenic, A. et al., “Development and performance evaluation of natural thermal-insulation materials composed of renewable resources,” Energy and Buildings, 43(9), 2011.↩︎

48. Wool fire properties: wool has a limiting oxygen index of approximately 25% (compared to approximately 17–18% for cotton), meaning it requires higher oxygen concentration to sustain combustion. It self-extinguishes when the ignition source is removed, does not melt or drip, and produces less toxic smoke than synthetic materials. See: Kozlowski, R.M. (ed.), Handbook of Natural Fibres, Woodhead Publishing.↩︎

49. Wool and formaldehyde absorption: Curling, S.F. et al., “An investigation of the ability of wool to absorb formaldehyde from indoor air,” Indoor and Built Environment, 21(5), 2012, pp. 720–724. The study demonstrated that wool fibre absorbs formaldehyde through an irreversible chemical reaction with keratin protein side chains (primarily the amino groups of lysine residues). This absorption capacity is a genuine additional benefit of wool insulation, though it is a secondary consideration compared to thermal performance.↩︎

50. NZ wool scouring: Cavalier Bremworth operates the largest NZ wool scouring facility at Awatoto, Napier (processing capacity approximately 100,000 tonnes per year of greasy wool). Other scouring operations exist at smaller scale. NZ’s total wool scouring capacity is well in excess of domestic insulation demand. See: NZ wool industry publications; Cavalier Bremworth company information.↩︎

51. Tallow soap vs. commercial scour detergent: commercial wool scouring uses anionic surfactants (typically sodium alkylbenzene sulphonate) that are highly effective at emulsifying lanolin. Tallow soap (sodium tallowate) is a weaker surfactant that requires higher concentrations and more wash cycles to achieve equivalent lanolin removal. Industrial wool scouring literature estimates 20–40% lower throughput when substituting soap for commercial detergent. See: Stewart, R.G., Woolscouring and Allied Technology, WRONZ, Christchurch.↩︎

52. Boron treatment for wool insulation: commercial wool insulation products are treated with 5–10% by weight of boron compounds (borax, boric acid, or sodium octaborate) which provide resistance to insects (moths, carpet beetles), mould, and fire. Boron acts as a flame retardant, insecticidal agent, and fungicide. NZ does not produce boron compounds — they are imported, primarily from Turkey and the US. See: NZ wool insulation manufacturer technical data; BRANZ research on natural insulation treatment.↩︎

53. Wool scouring yield: greasy wool contains approximately 40–60% impurities by weight (lanolin, suint, dirt, vegetable matter). Scouring yield (clean wool weight as a percentage of greasy weight) is approximately 45–65%, depending on breed and fleece quality. Crossbred wool typically has a higher scouring yield than fine merino. See: NZ Wool Testing Authority data; wool industry technical references.↩︎

54. Wool insulation thermal conductivity: published thermal performance data for commercial wool insulation products (e.g., Terra Lana, Woolhome, Thermafleece). Typical declared thermal conductivity is 0.035–0.040 W/m·K, which is comparable to fibreglass batts and within 10% of the best-performing mineral wool and cellulose products. See: manufacturer product data; BRANZ Appraisal certificates for NZ wool insulation products.↩︎

55. NZ cereal cropping area: Ministry for Primary Industries, SOPI reports; Stats NZ Agricultural Production Statistics. NZ has approximately 50,000–60,000 hectares of wheat and approximately 60,000–70,000 hectares of barley under normal conditions, concentrated in Canterbury (approximately 70% of national wheat area). Straw yield is approximately 3–5 tonnes per hectare. Under nuclear winter conditions, both area and yield decline (Doc #75).↩︎

56. Straw bale thermal performance: numerous studies. King, B., Design of Straw Bale Buildings, Green Building Press, 2006, cites R-values of approximately R-5 to R-7 for standard bale thickness (450 mm), depending on bale density, orientation, and plaster type. This is substantially better than the current NZ Building Code minimum for walls (R-1.9 to R-2.0 depending on climate zone).↩︎

57. Straw bale construction fire resistance: contrary to intuition, plastered straw bale walls perform well in fire tests. The compressed straw covered by lime or earth plaster does not readily ignite — the plaster provides an insulating barrier, and the tightly packed straw lacks sufficient oxygen for combustion. Straw bale walls have achieved fire resistance ratings of 60–120 minutes in testing. See: Apte, V. et al., “Fire Testing of Straw Bale Wall Systems,” Australasian Natural Building Association; Garas, G. et al., “Fire safety of straw bale buildings.”↩︎

58. Sawdust thermal conductivity: published thermal properties of wood-based loose-fill insulation. Sawdust and wood shavings have thermal conductivity in the range of 0.06–0.08 W/m·K, roughly double that of wool or cellulose. The higher conductivity means greater thickness is required for equivalent thermal resistance. See: Standard thermal properties references; Suleiman, B.M. et al., “Thermal conductivity of consolidated sawdust,” Wood and Fiber Science, 31(2), 1999.↩︎

59. Cellulose insulation thermal conductivity: commercial cellulose insulation products have declared thermal conductivity of approximately 0.035–0.042 W/m·K. This is comparable to fibreglass and wool insulation. See: manufacturer product data; BRANZ research on cellulose insulation performance.↩︎

60. Earth thermal conductivity: dry earth has thermal conductivity of approximately 0.5–1.5 W/m·K, depending on density, moisture content, and composition. Moist earth has higher conductivity (water fills air pores and conducts heat). Earth is not a good insulator in the conventional sense — its value is in thermal mass (high heat capacity, approximately 800–1,000 J/kg·K for dry earth). See: Standard building physics references; Minke, G., Building with Earth, Birkhauser.↩︎

61. Traditional Maori building: Best, E., “The Maori House and its Interior,” Government Printer, Wellington, 1924 (historical reference); Austin, M., “Polynesian Architecture in New Zealand,” PhD thesis, University of Auckland, 1976. Raupō (bulrush), toetoe, and other plant materials used in traditional whare construction provide both weather protection and insulation. While the building forms are different from modern NZ houses, the principle of using locally available plant materials for thermal protection is directly applicable.↩︎

62. NZS 4218:2009 (now superseded by H1/AS1 5th edition 2021): NZ Building Code clause H1 “Energy Efficiency” sets minimum insulation requirements for new buildings. Current ceiling requirements are approximately R-2.9 to R-3.3 depending on climate zone. Wall requirements are R-1.9 to R-2.0. Floor requirements are R-1.3. Under nuclear winter conditions, these minima are inadequate — higher R-values would be appropriate, but achieving even the current minima in the existing housing stock would represent a major improvement. See: MBIE, NZ Building Code; BRANZ.↩︎

63. Heat loss pathways in NZ houses: proportions are approximate and vary significantly with house design, age, and condition. The figures cited are broadly consistent with BRANZ research and NZ building science literature. See: Isaacs et al. (note 14); BRANZ bulletins on residential thermal performance.↩︎

64. Heat loss through open chimneys: an open fireplace chimney acts as a ventilation stack, drawing warm air out of the house continuously. Heat loss from an open chimney can represent 5–15% of total house heat loss depending on chimney size and wind conditions. Sealing unused chimneys is one of the highest-return draught-proofing measures. See: BRANZ research; energy efficiency literature on fireplace heat loss.↩︎

65. Draught-proofing effectiveness: various NZ and international studies show that systematic draught-proofing (sealing gaps around doors, windows, and service penetrations) reduces air leakage by 20–40% and heating energy demand by approximately 10–20%. The cost-effectiveness is very high — materials cost is minimal (foam strips, sealant) and labour time is modest. See: Energy Saving Trust (UK) research; BRANZ energy efficiency publications.↩︎

66. Window thermal resistance: single-glazed aluminium-framed windows have a total thermal resistance (including air films) of approximately R-0.15 m²K/W. Double-glazed windows with a 12 mm air gap have approximately R-0.26–0.34. Modern thermally broken double-glazed or triple-glazed units achieve R-0.45–0.70. An insulated wall (R-2.0 or more) is 13–15 times more thermally resistant than a single-glazed window. See: NZ Window Association; BRANZ; CIBSE Guide A.↩︎

67. Secondary glazing effectiveness: multiple studies show that DIY secondary glazing (plastic film or rigid sheet fixed inside the window frame) reduces window heat loss by 40–60% and improves the effective thermal resistance to approximately R-0.25–0.40 — approaching manufactured double glazing. See: Community Energy Action (Christchurch) research on secondary glazing; Energy Saving Trust (UK) publications.↩︎

68. Secondary glazing effectiveness: multiple studies show that DIY secondary glazing (plastic film or rigid sheet fixed inside the window frame) reduces window heat loss by 40–60% and improves the effective thermal resistance to approximately R-0.25–0.40 — approaching manufactured double glazing. See: Community Energy Action (Christchurch) research on secondary glazing; Energy Saving Trust (UK) publications.↩︎

69. Thermal curtain effectiveness: well-fitted thermal curtains with pelmets reduce window heat loss by approximately 40–60%, with the highest effectiveness when the curtain forms a sealed air pocket against the window (close-fitting to walls and sill). Curtains that hang freely are significantly less effective (approximately 15–25% reduction). See: BRANZ Study Reports on curtain effectiveness; French, L. et al., “Temperatures and heating energy in New Zealand houses from a household energy end-use study,” Energy and Buildings, 39(7), 2007.↩︎

70. Priority order of thermal interventions: this ordering reflects the general consensus in NZ building science (BRANZ, EECA) and international practice. Ceiling insulation and draught-proofing offer the highest return because they address the largest heat loss pathways with the least installation difficulty. Wall insulation is hardest because most NZ houses require either internal or external access to the wall cavity, which involves significant disruption. See: EECA guidance; BRANZ bulletins on insulation retrofit.↩︎

71. Warmer Kiwi Homes programme: administered by EECA (Energy Efficiency and Conservation Authority). https://www.eeca.govt.nz/co-funding/insulation-and-heaters/ — The programme provides 80–90% grants for ceiling insulation, underfloor insulation, and heating in eligible low-income homes. It uses accredited providers, standardised assessment, and quality assurance. Its predecessor (Warm Up New Zealand: Heat Smart) operated 2009–2016 and insulated approximately 300,000 homes.↩︎

72. Marae numbers: Te Puni Kokiri (Ministry for Maori Development) maintains information on NZ marae. There are approximately 700+ marae throughout NZ, though exact numbers and operational status vary. Many are in rural areas. Urban marae serve as important community hubs. See: Te Puni Kokiri; iwi websites and publications.↩︎

73. NZ school numbers: Ministry of Education, “Education Counts.” https://www.educationcounts.govt.nz/ — NZ has approximately 2,500 state and state-integrated schools as of 2024. The figure includes primary, intermediate, secondary, and composite schools. Most have at least one hall or assembly space and heated classrooms that could serve as community warming centres outside school hours.↩︎

74. Community heating energy comparison: the estimates are based on engineering rules of thumb for building heat loss. A typical community hall (200–400 m² floor area, moderate insulation) loses approximately 10–25 kW at a 20°C indoor-outdoor temperature differential. A typical NZ house (100–150 m² floor area, poor to moderate insulation) loses approximately 2–5 kW at the same differential. The comparison assumes 50 people distributed across 25–35 houses (1.4–2.0 people per household). Actual figures vary significantly with building design, insulation level, wind exposure, and outdoor temperature. The key point — that shared spaces use less energy per person than individual houses — is robust across all reasonable assumptions. See: CIBSE Guide A, “Environmental Design”; BRANZ heat loss calculation methods.↩︎

75. Warm Up New Zealand: Heat Smart programme: approximately 300,000 homes insulated between 2009 and 2016, at a total programme cost of approximately NZ$370 million (government and homeowner contributions combined). The programme was evaluated by Motu Economic and Public Policy Research (see note 11) and found to have significant health and energy benefits. See: EECA programme reports; Motu Working Papers.↩︎

76. Healthy Homes Standards: Residential Tenancies (Healthy Homes Standards) Regulations 2019. These set minimum standards for insulation, heating, ventilation, moisture management, and draught stopping in all rental properties. Compliance deadlines were phased between 2021 and 2025. The standards provide a practical benchmark for minimum acceptable housing thermal performance. See: MBIE, “Healthy Homes Standards.” https://www.tenancy.govt.nz/healthy-homes/↩︎