Doc #164 — Timber Construction (NZ Seismic)

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RECOMMENDED ACTIONS (BY URGENCY)

NZ’s existing housing stock does not disappear on day one. People have roofs. The construction workforce is important, but in the first months the government is managing food rationing, medical triage, fuel allocation, power grid continuity, and basic public order — all of which have immediate life-or-death consequences. Seismic timber construction matters, but the buildings that need it do not need to be designed and built in the first month. This programme starts in earnest in Year 1 and scales through Years 2–5.

First year

1. Include construction workforce in national skills census (Doc #8). Builders, building inspectors, and structural engineers are recovery assets — but identifying them through the census is sufficient. They do not need a separate “essential worker” classification in the first weeks when nobody is building anything yet.
2. Inventory fastener stocks nationally — nails, screws, bolts, joist hangers, framing brackets, gang-nail plates. Establish depletion timeline at projected consumption rates. This can be done as part of the broader stockpile audit (Doc #1) and does not require its own dedicated team in the first month.
3. Issue interim construction guidance: All new construction to use standard NZ timber framing (NZS 3604 principles) with emphasis on material conservation — minimise fastener use through design, avoid proprietary systems where standard alternatives exist.
4. Secure plywood and engineered timber stocks — plywood, LVL (laminated veneer lumber), and glulam are high-value products with limited domestic production capacity. Prioritise for bracing and structural applications.
5. Assess plywood production continuity — NZ has several plywood and LVL plants (Nelson Pine Industries, Carter Holt Harvey, Juken New Zealand). These require phenol-formaldehyde or other adhesives, most of which are imported. Determine adhesive stocks and depletion timelines. Investigate NZ-producible adhesives (casein from milk, blood albumin, tannin-based adhesives).
6. Establish regional timber grading capability — trained graders at major sawmills to visually grade structural timber to NZS 3631. Structural timber must be graded to be used safely; ungraded timber cannot be assigned design properties.

Years 1–3

7. Develop and distribute recovery-adapted construction details — connection designs using nails, bolts, and timber joinery that provide equivalent seismic performance to proprietary connectors. These should be developed by structural engineers familiar with NZS 3604 and NZS 3603 and distributed as printed building guides.
8. Begin training builders in traditional joinery methods — pegged mortise-and-tenon, housed joints, half-lap joints, and wedged through-tenons. These require 2–4 weeks of dedicated workshop instruction per builder (see Section 8.2) and are not currently taught in NZ building apprenticeships. Training through polytechnic programmes (Doc #159) and on-site mentoring from heritage builders (Doc #157).
9. Recovery-era building code guidance operational — a simplified, printed manual based on NZS 3604 principles but adapted for available materials and fasteners. This is a practical interpretation of existing code principles for recovery conditions.
10. Nail and bolt production from NZ wire (Doc #105) at sufficient scale to support construction programme.
11. Foundation guidance issued — standardised designs for timber pile foundations, concrete pad foundations (minimal cement use), and ground improvement techniques for NZ soils.
12. Pilot multi-storey timber buildings (2–3 storeys) using heavy timber framing and timber-pegged joinery, demonstrating that medium-density housing is achievable without steel fasteners at every connection.

Years 3–5

13. Scale construction programme to address housing demand — new builds, earthquake strengthening, and repair of damaged housing.
14. Develop NZ-produced adhesives for plywood and glulam production — casein, blood albumin, or tannin-formaldehyde from NZ pine bark.
15. Transition to locally produced fasteners as imported stock depletes — nails, bolts, coach screws from NZ steel.
16. Establish building inspection and quality assurance systems appropriate to recovery conditions — the consequences of poor construction in a seismic country are severe.

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ECONOMIC JUSTIFICATION

The housing deficit

NZ entered the recovery scenario with a pre-existing housing shortage estimated at 20,000–50,000 dwellings, concentrated in Auckland.⁶ Nuclear winter conditions increase demand further: household consolidation (multiple families sharing dwellings for warmth — Doc #146), population relocation from worst-affected regions, and possible refugee intake all affect housing requirements. Meanwhile, the existing housing stock degrades — approximately 1% of NZ’s 1.8 million dwellings suffer significant damage or reach end-of-life each year under normal conditions, and earthquakes, severe weather, and deferred maintenance under recovery conditions accelerate this.

A recovery-era construction programme building 5,000–15,000 dwellings per year is a reasonable estimate of sustained need. NZ built approximately 35,000–45,000 new dwellings per year in the early 2020s, so 5,000–15,000 per year is a substantial reduction — but it must be achieved with reduced material availability and a workforce competing with other recovery demands.⁷

Labour

A typical NZ timber-framed house requires approximately 800–2,000 person-hours for construction, depending on size, complexity, and finish level.⁸ A simplified recovery-era dwelling (smaller footprint, simpler detailing, less interior finishing) might require 600–1,200 person-hours. At 10,000 houses per year, this represents approximately 6,000,000–12,000,000 person-hours, or roughly 3,000–6,000 full-time-equivalent construction workers. NZ has approximately 60,000–80,000 people in residential building trades, so the construction programme absorbs roughly 4–10% of the existing construction workforce — a manageable allocation.⁹

Material cost

A typical NZ single-storey 3-bedroom house (approximately 100–120 m² floor area) requires approximately:¹⁰

• Timber framing: 10–15 m³ of structural timber (radiata pine or Douglas fir)
• Cladding and lining: 5–10 m³ of timber boards or panels
• Roofing: Steel roofing (from NZ Steel) or timber shingles
• Foundation: 2–5 m³ of concrete (timber piles reduce this substantially)
• Fasteners: 20–40 kg of nails, bolts, and connectors
• Insulation: Wool, sawdust, or other NZ material (Doc #163)

All of these are NZ-producible. The timber requirement of 15–25 m³ per house, at 10,000 houses per year, is 150,000–250,000 m³ — less than 10% of NZ’s current domestic sawn timber production (approximately 4.5–5 million m³ per year).¹¹ Timber supply is not a constraint on the construction programme.

Opportunity cost and return

The alternative to building adequate housing is people living in damaged, overcrowded, or uninsulated dwellings. The health costs of inadequate housing under nuclear winter conditions are substantial (Doc #163 estimates excess winter mortality of 3,000–6,000 per year without intervention). Construction workers building houses are simultaneously reducing health system demand, preserving workforce capacity (healthy people work; sick people do not), and creating durable infrastructure. This is among the highest-return labour allocations available.

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1. NZ TIMBER SPECIES FOR CONSTRUCTION

1.1 Radiata pine (Pinus radiata)

Radiata pine is NZ’s dominant construction timber, comprising approximately 90% of the plantation estate (~1.53 million hectares) and the overwhelming majority of structural timber used in NZ building.¹²

Structural properties (SG8 grade — the most common NZ structural grade):¹³

Property	Value
Bending strength (MOR)	14.0 MPa (characteristic, 5th percentile)
Modulus of elasticity (MOE)	8,000 MPa (lower bound)
Compression parallel to grain	18.0 MPa
Shear	3.8 MPa
Density (dry)	420–500 kg/m³
Durability class (heartwood)	Class 4 (not durable)

SG8 is the minimum structural grade for most NZS 3604 applications. Higher grades (SG10, SG12) are available from selected logs and provide higher strength values — SG10 has a characteristic MOE of 10,000 MPa and is specified for longer spans and higher loads.¹⁴

Advantages: Abundantly available, fast-growing (25–30 year rotation), easy to work with hand and machine tools, light weight, good nail-holding properties, well-characterised structural properties, compatible with existing NZ building practice.

Limitations: Poor natural durability — requires treatment for any application involving moisture exposure or ground contact (Doc #99, Section 5). Without treatment, radiata pine in ground contact may fail in 2–5 years from decay. Structural integrity can be compromised by borer (Anobium punctatum) in untreated sapwood.

1.2 Douglas fir (Pseudotsuga menziesii)

Douglas fir occupies approximately 100,000 hectares of NZ’s plantation estate, concentrated in the South Island (Canterbury, Otago, Southland) and Nelson/Marlborough.¹⁵

Structural properties (No. 1 Framing grade):¹⁶

Property	Value
Bending strength (MOR)	~18–24 MPa (characteristic, depending on grade)
Modulus of elasticity (MOE)	9,000–12,000 MPa
Compression parallel to grain	~20–25 MPa
Density (dry)	480–560 kg/m³
Durability class (heartwood)	Class 3 (moderately durable)

Advantages: Stronger and stiffer than radiata pine — approximately 15–30% higher bending strength and MOE for equivalent grades. Heartwood has moderate natural durability (useful where treatment is unavailable). Better resistance to splitting when nailed near edges. Superior for heavy structural applications — beams, posts, headers.

Limitations: Less available than radiata pine. Slower growing (35–45 year rotation in NZ). Can be more difficult to work — harder, more prone to checking during drying. Not available in all regions.

1.3 Macrocarpa (Cupressus macrocarpa)

Not a plantation timber in the conventional sense — macrocarpa is widespread throughout NZ as shelterbelts, farm trees, and amenity plantings. Total resource is difficult to quantify but substantial, particularly in rural areas.¹⁷

Structural properties:¹⁸

Property	Value
Bending strength (MOR)	~40–60 MPa (clear wood; structural grades lower)
Modulus of elasticity (MOE)	6,000–8,000 MPa
Density (dry)	450–530 kg/m³
Durability class (heartwood)	Class 2 (durable)

Advantages: Excellent natural durability — heartwood macrocarpa resists decay and borer without chemical treatment. Suitable for ground-contact applications (piles, posts), exterior cladding, and any situation where untreated radiata pine would fail. Widely distributed throughout NZ.

Limitations: Not available in standardised structural grades — each tree and each piece must be assessed individually. Highly variable properties depending on growth conditions. Contains knots and defects that affect structural performance. MOE is lower than radiata pine SG8, meaning wider or deeper sections may be needed for equivalent spans. Not suitable as a primary framing timber for large programmes due to limited and variable supply.

Strategic role: Reserve macrocarpa for applications where natural durability is essential — piles, posts, bearers in ground contact, exterior cladding. Do not use macrocarpa where treated radiata pine (while treatment stocks last) or untreated radiata pine (in dry interior applications) would serve.

1.4 Native species

NZ native timbers — totara, rimu, kahikatea, matai, beech — have excellent properties for construction (particularly totara, which is Class 1 durability and was the preferred Maori building timber). However, native forest logging is heavily restricted for sound ecological and cultural reasons (Doc #99, Section 9). Under recovery conditions, native timber for construction is limited to:

• Salvage and recycled timber from demolished pre-1970s buildings (many built with native timber)
• Naturally fallen trees accessible without live-tree harvest
• Emergency selective harvest of private native stands, only as a last resort and in genuine partnership with tangata whenua

Native timber should be reserved for high-value applications where its properties are genuinely needed — durable piles and posts (totara), marine construction, and heritage or cultural buildings.¹⁹

1.5 Species selection guide for construction

Application	First choice	Second choice	Notes
Wall framing (interior, dry)	Radiata pine SG8	Douglas fir	Untreated acceptable if kept dry
Wall framing (within 150 mm of ground)	Treated radiata pine	Macrocarpa, Douglas fir	Treatment while stocks last; then naturally durable species
Floor joists	Radiata pine SG8/SG10	Douglas fir	Douglas fir superior for longer spans
Rafters	Radiata pine SG8	Douglas fir
Bearers	Treated radiata pine, Douglas fir	Macrocarpa	Ground proximity requires durability
Piles	Macrocarpa, treated radiata	Totara (salvage only)	Ground contact — natural durability essential long-term
Exterior cladding	Charred radiata, macrocarpa	Pine-tar treated radiata	See Doc #99
Heavy beams and posts	Douglas fir	Radiata pine SG10+	Douglas fir preferred for heavy structural
Roof purlins	Radiata pine SG8	Douglas fir

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2. SEISMIC DESIGN PRINCIPLES FOR TIMBER BUILDINGS

2.1 Why timber performs well in earthquakes

Timber-framed buildings have consistently performed well in NZ earthquakes. In the Canterbury earthquake sequence, timber-framed houses suffered far less structural damage than unreinforced masonry, concrete frame, or heavy construction types — the majority of timber-framed houses in Christchurch remained structurally sound, even where foundations were damaged by liquefaction or lateral spreading.²⁰

The reasons are physical:

• Low mass. Earthquake forces are proportional to mass (F = ma). A timber-framed house weighs roughly 5–15 tonnes for a typical single-storey dwelling, compared to 50–150 tonnes for an equivalent masonry or concrete structure. Lower mass means lower earthquake forces, which means lighter framing can resist those forces.
• Ductility. Timber connections (nailed, bolted, or pegged) deform before they break. This ductility absorbs earthquake energy through deformation rather than sudden brittle failure. A nailed plywood joint can undergo significant deformation while still carrying load — this is the mechanism that gives timber framing its earthquake resilience.²¹
• Redundancy. A timber-framed house has hundreds of connections. If individual connections fail, load redistributes to neighbouring connections. This redundancy prevents progressive collapse — the loss of one connection does not cause the building to fall.
• Repairability. Damaged timber framing can be repaired — replace a cracked stud, re-nail a loosened connection, jack and re-level a shifted foundation. Damaged concrete or masonry structures are often beyond economical repair.

2.2 NZ seismic hazard zones

NZ’s seismic hazard varies significantly by location. NZS 1170.5 (Structural Design Actions — Earthquake Actions) defines hazard zones based on the probabilistic seismic hazard model maintained by GNS Science.²² The key parameter for building design is the zone hazard factor Z:

Location	Z factor (approximate)	Seismic demand
Auckland	0.13	Low
Hamilton	0.13	Low
Tauranga	0.20	Moderate
Napier	0.38	High
Wellington	0.40	Very high
Nelson	0.27	Moderate–High
Christchurch	0.30	High
Dunedin	0.13	Low
Invercargill	0.17	Moderate

Source: NZS 1170.5 Table 3.3, approximate values for the relevant site classes.²³

Implication for construction: A house in Wellington must resist approximately three times the earthquake forces of an identical house in Auckland. This affects bracing requirements, connection design, and foundation details. Recovery-era construction guidance must be zone-specific — a single set of details is not appropriate for all of NZ.

2.3 NZS 3604 — the timber-framed buildings standard

NZS 3604 is the prescriptive standard that governs the vast majority of NZ residential timber construction. It is a “deemed-to-comply” standard — meaning that a building designed and constructed in accordance with NZS 3604 is automatically deemed to comply with the NZ Building Code (specifically clauses B1 Structure, B2 Durability, and E2 External Moisture).²⁴

NZS 3604 covers:

• Timber sizes and grades for all framing members (studs, plates, joists, rafters, lintels, beams)
• Span tables specifying maximum allowable spans for each member size, grade, and loading condition
• Bracing requirements by seismic zone and wind zone
• Foundation design (concrete slabs, concrete piles, timber piles)
• Connection details (nailing schedules, bolt specifications, connector requirements)
• Specific construction methods for walls, floors, roofs, and subfloor structures

Under recovery conditions, NZS 3604 remains the primary design reference. It should not be abandoned or replaced — it represents decades of NZ-specific engineering knowledge adapted to NZ’s seismic, wind, and climatic conditions. What changes is the available materials for implementing its requirements — different fasteners, different bracing systems, different foundation materials. The principles remain sound; the details adapt.

2.4 Bracing — the critical seismic element

In a timber-framed building, vertical loads (gravity — the weight of the building and its contents) are carried by the framing members themselves. But horizontal loads — earthquake forces and wind — must be resisted by bracing: elements that prevent the frame from racking (deforming sideways under horizontal force like a parallelogram).

Current NZS 3604 bracing methods:

1. Plywood sheathing — structural plywood nailed to timber framing. The most common and most efficient NZ bracing method. A standard 2.4 m high x 0.9 m wide plywood-braced panel provides 75–150 bracing units (BU) depending on panel configuration and nailing pattern.²⁵
2. Proprietary bracing systems — GIB Braceline (plasterboard with specific fixing), Plyline, steel angle bracing, diagonal steel strapping. These are manufactured products with tested and rated bracing capacities.
3. Diagonal timber bracing — let-in timber diagonal braces (typically 100 x 25 mm timber let into notches in the studs at approximately 45 degrees). An older method, less efficient than plywood but functional. Rated at approximately 30–50 BU per panel depending on configuration.²⁶
4. Board sheathing — horizontal or diagonal timber boards nailed to the exterior face of the framing. Provides bracing through the shear resistance of the nailed board connections. This is the oldest timber bracing method in NZ and was standard before plywood became widely available (post-1960s).

Recovery-era bracing strategy: Plywood bracing is the preferred method while supply lasts — it is the most efficient use of material and provides the best seismic performance. When plywood becomes scarce (due to adhesive depletion limiting production), the transition path is:

• First priority: Maximise plywood production for as long as adhesive is available. Investigate NZ-producible adhesives (Section 7).
• Second priority: Use board sheathing (timber boards 150–200 mm wide, nailed diagonally or horizontally to framing). This is less efficient — a board-sheathed wall provides perhaps 30–60% of the bracing capacity of an equivalent plywood-sheathed wall — requiring more braced wall length to achieve the same total bracing.²⁷
• Third priority: Diagonal timber braces let into framing, supplemented by board sheathing. Adequate for low-to-moderate seismic zones (Auckland, Dunedin, Invercargill). In high seismic zones (Wellington, Napier, Christchurch), additional braced wall length is needed.
• For all methods: Nailing is critical. Bracing performance depends on the number, spacing, size, and quality of nails attaching the bracing to the framing. Inadequate nailing is the single most common bracing failure mode. Construction training and inspection must emphasise nailing discipline.

2.5 Bracing demand by zone

NZS 3604 specifies bracing demand in bracing units (BU) based on building weight, seismic zone, wind zone, and building geometry. A rough guide for a typical single-storey timber-framed house (100–120 m² floor area, light roof cladding):²⁸

Seismic zone	Approximate seismic bracing demand (BU)	Approximate wind bracing demand (BU)
Low (Z ≤ 0.15, Auckland/Dunedin)	50–100	60–150 (depends on wind zone)
Moderate (Z ~ 0.20, Tauranga)	80–130	60–150
High (Z ~ 0.30, Christchurch)	120–180	60–150
Very High (Z ~ 0.40, Wellington)	150–250	80–200

These are rough indicative values. Actual demand must be calculated for each building based on its specific characteristics using NZS 3604 or NZS 1170.5.²⁹

In low seismic zones, wind loading often governs bracing demand — the building needs more bracing for wind than for earthquake. In high seismic zones, earthquake loading governs. Recovery-era construction guidance should provide pre-calculated bracing solutions for common building configurations in each zone.

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3. TIMBER CONNECTIONS WITHOUT IMPORTED FASTENERS

3.1 The fastener problem

NZ’s current timber construction system depends on manufactured steel fasteners:

• Nails (hand-driven and gun-driven) — the primary framing connection. A typical NZ house uses 20,000–40,000 nails.³⁰
• Screws (bugle-head, hex-head, coach screws) — for critical connections, hardware attachment, and withdrawal-loaded joints.
• Bolts (M12, M16, M20) — for heavy connections, hold-down brackets, and foundation attachments.
• Proprietary connectors — joist hangers, post bases, gang-nail plates (for trusses), framing brackets, hold-down straps, and seismic connectors.

NZ imports virtually all fasteners. Doc #105 describes wire drawing and nail production from NZ steel (Glenbrook wire rod production) — this is feasible and should be a high priority. However, the full range of proprietary connectors cannot be replicated domestically in the near term. The construction programme must adapt to use simpler fastening methods.

3.2 Nailed connections — the backbone

Nails remain the primary connection method. NZ can produce nails from Glenbrook steel (Doc #89 for steel production; Doc #105 for wire drawing and nail manufacture). The key requirement is sufficient nail stock or domestic production. NZS 3604 specifies nailing schedules for all connections — number of nails, size, and spacing for each joint type. These schedules are engineered and must be followed; random nailing is not acceptable.

Critical nailing requirements (NZS 3604):³¹

Connection	Nail size	Minimum nails
Stud to bottom plate	2 x 90 mm	Skew-nailed each side
Stud to top plate	2 x 90 mm	End-nailed or skew-nailed
Joist to bearer	2 x 75 mm	Skew-nailed each side
Rafter to top plate	3 x 90 mm	Skew-nailed
Bracing ply to framing	50 mm at 150 mm centres	On edges; 300 mm centres on intermediate studs
Bottom plate to foundation	12 mm bolts at 1.2 m max	Not nails — bolted

3.3 Bolted connections

Bolts provide higher-capacity connections than nails and are essential for:

• Foundation hold-downs (timber frame to concrete or timber pile)
• Beam-to-post connections
• Heavy timber connections in multi-storey construction
• Seismic hold-down straps and brackets

NZ can produce bolts from Glenbrook steel, though bolt production requires threading capability (Doc #91 — Machine Shop Operations). The dependency chain is: Glenbrook iron sand smelting (Doc #89) produces steel billets → wire rod rolling → wire drawing to bolt stock diameter (Doc #105) → cutting to length → head forming (upset forging, requiring a heading die and hammer or press) → thread cutting (requiring a threading die set or lathe with thread-cutting capability). The critical sizes for timber construction are M12, M16, and M20. A bolt production workshop with a threading lathe or die set can supply regional construction demand from locally drawn steel rod, but establishing this capability requires machine shop infrastructure and tooling that may take 6–18 months to commission under recovery conditions.

3.4 Pegged joints (timber dowels)

Pegged joints — connections made using hardwood dowels driven through pre-drilled holes in the mating timber members — are one of the oldest and most reliable timber connection methods. They predate metal fasteners by thousands of years and remain in use today for heavy timber construction worldwide.³²

How they work: A hardwood dowel (typically 20–30 mm diameter) is driven through aligned holes in two or more timber members. The dowel transfers load through bearing (compression) between the dowel surface and the timber. Multiple dowels distribute the load across the joint. The joint can be further secured by wedging the dowel ends.

Properties: - Ductile behaviour — the dowel and surrounding timber deform under overload before ultimate failure, providing earthquake-compatible energy absorption. - Strength comparable to bolted connections of similar dowel diameter — a 25 mm hardwood dowel has bearing capacity similar to an M16 bolt, though without the clamping force a bolt provides. - Self-tightening — timber dowels swell slightly with moisture, tightening in the hole. (This is also a limitation — excessive swelling can split the surrounding timber.) - No corrosion — timber dowels do not rust, corrode, or degrade the surrounding wood through galvanic reaction.

Dowel material: The dowel must be harder and denser than the framing timber. Suitable NZ species: - Rata — very hard, dense, excellent dowel material where available from salvage - Manuka — hard, dense, widely available (manuka grows prolifically across NZ, including on marginal land) - Kanuka — similar to manuka - Beech — hard beech and red beech are suitable - Dense macrocarpa — heartwood from older trees - Oak — if available from amenity plantings or salvage

Manuka is the most practically available hardwood for dowels — it grows on disturbed land throughout NZ, coppices well, and can be harvested sustainably on short rotations (5–10 years for dowel-sized stems).³³

3.5 Mortise-and-tenon joints

The mortise-and-tenon is the fundamental joint of heavy timber construction — a projecting tongue (tenon) cut on one member fits into a matching rectangular hole (mortise) cut in the other. The joint is secured with one or more timber dowels driven through the mortise cheeks and through the tenon.³⁴

Applications in recovery-era construction:

• Post-to-beam connections — the beam tenon fits into the post mortise. This replaces bolted brackets and joist hangers.
• Beam-to-beam connections — housed or shouldered mortise-and-tenon for intersecting beams.
• Rafter-to-ridge and rafter-to-plate connections — tenoned or birdsmouth-and-pegged connections.
• Bracing connections — diagonal braces tenoned into posts and beams.

Structural performance: Mortise-and-tenon joints have well-documented structural properties. A properly fitted, pegged mortise-and-tenon in radiata pine or Douglas fir can carry loads comparable to bolted connections of similar scale. The joint’s capacity is limited by the tenon’s bearing area, the peg shear capacity, and the mortise’s resistance to splitting.³⁵

Labour cost: This is the primary disadvantage. A nailed stud-to-plate connection takes seconds. A mortise-and-tenon joint takes 15–60 minutes to lay out and cut, depending on the builder’s skill and available tools. Power tools (a drill press, mortising machine, or router) accelerate the work substantially; hand tools alone (chisel and mallet) are slow. The economic equation favours mortise-and-tenon for heavy timber connections (where the alternative is expensive bolted brackets) and nails for light framing (where the labour cost of joinery exceeds the material cost of nails).

3.6 Notched and housed joints

Simpler than full mortise-and-tenon, notched joints involve cutting a housing (notch) in one member to receive the bearing end of another. Used for:

• Joist-to-bearer connections: A notch in the top of the bearer receives the joist end, providing bearing support without joist hangers.
• Rafter birdsmouth: The rafter is notched to sit over the top plate, providing bearing and resistance to outward thrust. This is standard NZ practice already — NZS 3604 specifies birdsmouth cuts for rafters.³⁶
• Let-in bracing: A diagonal brace notched into the face of the studs, providing racking resistance without separate bracing panels.
• Halving joints (half-laps): Two members notched to half their depth, overlapping at the intersection. Used for crossing members, plate splices, and low-load connections.

Notched joints are simpler and faster than mortise-and-tenon, but provide lower capacity — they rely primarily on bearing and friction, with nails or pegs providing secondary restraint. They are appropriate for lighter loads and where the connection does not need to resist large tension or shear forces.

3.7 Combined fastening strategy

The practical approach is not exclusively traditional joinery or exclusively nailed construction — it is a combination matched to the connection’s requirements:

Connection type	Recommended fastening method
Light framing (studs, plates, nogs)	Nails (NZ-produced)
Bracing panel to framing	Nails at specified spacing
Joist to bearer	Notched bearing + skew nails
Rafter to top plate	Birdsmouth notch + nails
Post to beam (heavy timber)	Mortise-and-tenon + hardwood pegs
Beam to beam	Housed joint + bolts or pegs
Foundation hold-down	Bolts (NZ-produced)
Truss assembly	Nails + gusset plates (plywood or timber)
Ridge connection	Halving joint + bolts or pegs

This strategy uses manufactured fasteners (nails, bolts) where they are most efficient and reserves labour-intensive joinery for connections where it provides the greatest structural and material-saving benefit.

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4. SPAN TABLES FOR NZ SPECIES

4.1 How span tables work

Span tables specify the maximum allowable distance a timber member can span between supports, for a given member size, timber grade, and loading condition. NZS 3604 contains span tables for all common framing members. These tables are the primary design tool for NZ residential construction — builders select member sizes directly from the tables without needing to perform structural calculations.³⁷

The following tables are simplified extracts for common residential applications. They assume SG8 grade radiata pine (the most commonly available NZ structural timber), standard NZ live and dead loads, and single-span conditions. Douglas fir spans are approximately 10–15% longer for the same section size due to higher stiffness.

4.2 Floor joists (residential live load — general, 1.5 kPa)

Joist size (mm)	Maximum span at 400 mm spacing	Maximum span at 600 mm spacing
140 x 45	2.4 m	2.1 m
190 x 45	3.2 m	2.8 m
240 x 45	4.1 m	3.5 m
290 x 45	4.7 m	4.1 m
190 x 90	4.1 m	3.6 m
240 x 90	5.2 m	4.6 m

Source: Derived from NZS 3604 Table 7.1 principles. Exact values should be verified against the current standard. Spans shown are approximate and conservative.³⁸

4.3 Bearers

Bearer size (mm)	Maximum span (single storey, light construction)
140 x 90	1.8 m
190 x 90	2.4 m
240 x 90	3.1 m
290 x 90	3.5 m
240 x 140 (or double 240 x 90)	4.0 m

Source: NZS 3604 bearer tables, approximate values for typical NZ residential loading.³⁹

4.4 Rafters (light roof cladding — steel or timber shingles)

Rafter size (mm)	Maximum span at 600 mm spacing (roof pitch 15–35 degrees)
90 x 45	1.8 m
140 x 45	2.8 m
190 x 45	3.8 m
240 x 45	4.8 m

Source: NZS 3604 rafter tables, approximate values for light cladding.⁴⁰

4.5 Lintels (window and door headers)

Lintel size (mm)	Maximum span (single storey, light roof)
190 x 45 (single)	1.2 m
190 x 45 (double)	1.8 m
240 x 45 (double)	2.4 m
290 x 45 (double)	3.0 m
240 x 90	2.7 m

Source: NZS 3604 lintel tables, approximate values.⁴¹

Important limitations of these tables: The values shown are approximate and intended to convey the general magnitude of allowable spans. Actual construction must use the full NZS 3604 tables, which account for specific loading conditions, support conditions, continuity, and other factors. Using the wrong table or applying it to an incorrect loading scenario can result in undersized members and structural failure — potentially during an earthquake when the consequences are most severe. Builders and designers should have access to a complete copy of NZS 3604 or equivalent printed guidance.

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5. FOUNDATION OPTIONS

5.1 The foundation challenge

Foundations transfer building loads to the ground and anchor the building against earthquake and wind forces. NZ’s seismic environment demands robust foundation connections — buildings have been observed to slide off foundations during earthquakes when connections were inadequate.⁴²

Current NZ foundations are predominantly:

• Concrete slab-on-ground — a reinforced concrete slab (typically 100–150 mm thick) on compacted fill. The most common foundation for new NZ houses. Depends on cement (Doc #97) and rebar (Doc #97, Section 7).
• Concrete pile and bearer — concrete piles (typically 200–350 mm diameter, cast in drilled holes) supporting timber bearers and a suspended timber floor. Uses less concrete than a slab but still requires rebar for the pile reinforcement.
• Timber pile and bearer — round timber piles driven or placed in excavated holes, supporting timber bearers. This is the traditional NZ foundation method (standard before concrete became cheap) and remains permitted under NZS 3604 using treated timber piles.

5.2 Timber pile foundations

Under recovery conditions, timber pile foundations become the preferred option for most residential construction because they minimise concrete and rebar demand.

Pile material: - Treated radiata pine (H5 treatment) — while CCA treatment stocks last, approximately Class 4 durability in ground contact with 40–60 year service life. - Macrocarpa heartwood — Class 2 natural durability, expected service life in ground contact of 15–30 years depending on soil conditions.⁴³ No treatment required. - Totara heartwood — Class 1 (very durable), 30–50+ year service life in ground contact. Available only from salvage or emergency native harvest (Doc #99, Section 9). - Charred radiata pine — surface charring with pine tar application may extend untreated radiata pine ground-contact life to 10–20 years (Doc #99, Section 5.3). Insufficient field data for NZ conditions; trials needed.

Design: - Typical pile diameter: 150–250 mm for single-storey residential. - Pile depth: minimum 600 mm embedment in firm ground; deeper in soft soils. NZS 3604 specifies minimum embedment depths. - Pile spacing: typically 1.2–2.4 m, depending on bearer span and loading. - Bearers bolted to pile tops using M16 bolts through pre-drilled holes. The bolt connection provides the critical resistance to horizontal earthquake forces — uplift and sliding restraint.

Seismic connections: - Timber piles must be braced against lateral forces. Options include: - Concrete infill in the annulus around the pile (minimal concrete — perhaps 5–10 litres per pile, compared to hundreds of litres for a full concrete pile) - Diagonal timber bracing between piles below floor level - Embedment in compacted gravel with a concrete collar at ground level - Bearer-to-pile connections must resist both uplift (holding down the building during earthquake vertical acceleration) and horizontal sliding. Through-bolting with large washers provides this resistance.

5.3 Concrete pad foundations

A hybrid approach: small concrete pads (300–600 mm square, 200–300 mm deep) cast on the ground at each pile location, with timber piles or posts bolted to cast-in steel brackets or standing on the pad surface with a bolt connection. This uses very little concrete (perhaps 0.5–1 m³ total for a small house, compared to 10–15 m³ for a full slab) while providing a durable, level bearing surface for timber piles.⁴⁴

Concrete pads can be unreinforced (no rebar) for small residential buildings on good ground. The pad distributes the pile load to the soil; the bolt connection through the pad resists uplift and sliding.

5.4 Ground conditions and liquefaction

NZ’s seismic environment includes a significant liquefaction risk — saturated loose sandy or silty soils that lose strength during earthquake shaking, causing buildings to sink, tilt, or slide. Canterbury’s liquefaction in 2010–2011 damaged thousands of buildings, many on timber piled foundations.⁴⁵

Under recovery conditions, liquefaction-prone sites should be avoided for new construction where possible. Identifying these sites requires geotechnical knowledge — NZ has published liquefaction susceptibility maps for many urban areas based on the Canterbury experience.⁴⁶ Where construction on liquefaction-prone ground is unavoidable:

• Use deeper piles through the liquefiable layer into firm bearing ground
• Use raft-style timber foundations (closely spaced piles connected by a rigid floor platform) that resist differential settlement
• Accept that some liquefaction damage is likely in a major earthquake and design for repairability — timber buildings on piles are easier to relevelled after liquefaction than slab-on-ground buildings

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6. MULTI-STOREY TIMBER CONSTRUCTION

6.1 Why multi-storey matters

Population consolidation under nuclear winter (Doc #149) and the need to house more people efficiently favour denser housing. Two-storey and three-storey timber buildings provide roughly twice or three times the floor area on the same footprint, reducing both land use and foundation material requirements per dwelling.

6.2 NZS 3604 scope

NZS 3604 covers timber-framed buildings up to three storeys and 10 m in height, provided certain conditions are met (residential use, light cladding, specific floor area limits). Two-storey timber framing is standard NZ practice and requires no special engineering beyond NZS 3604’s prescriptive requirements, which include heavier framing members for the lower storey, increased bracing, and stronger foundation connections.⁴⁷

Three-storey timber framing is within NZS 3604 scope but pushes the prescriptive standard’s limits — particularly for bracing and connection design. In high seismic zones, specific engineering design (NZS 3603) may be required rather than the prescriptive NZS 3604 approach.

6.3 Heavy timber framing for multi-storey

For two-storey and three-storey construction, particularly where modern proprietary connectors are unavailable, heavy timber framing offers advantages:

• Larger section sizes (150 x 150, 200 x 200, 250 x 250 mm posts and beams) provide higher individual member capacity, reducing the number of connections.
• Mortise-and-tenon joinery with hardwood pegs is particularly suited to heavy timber — the larger sections allow well-proportioned joints with adequate bearing area and peg capacity.
• Exposed structure — heavy timber framing can be left exposed as the finished interior surface, eliminating the need for separate interior lining and reducing material use.
• Fire performance — large timber sections char predictably in a fire (approximately 0.6–0.8 mm per minute), maintaining structural integrity for extended periods. A 200 mm x 200 mm post exposed on all four sides retains an uncharred core of approximately 160 mm x 160 mm after 30 minutes — roughly 64% of its original cross-sectional area and a substantial fraction of its load-carrying capacity — a counterintuitive advantage of heavy timber over light framing, which fails more quickly.⁴⁸

6.4 Seismic performance of multi-storey timber

The seismic challenge increases with height. A three-storey building experiences significantly higher earthquake forces than a single-storey building of the same plan area — both because the total mass is greater and because the dynamic amplification at upper levels increases forces beyond the base shear level.

Design approaches:

• Braced frames: The same plywood or board sheathing approach used in single-storey construction, extended to multiple storeys. Each storey must have sufficient bracing for the cumulative earthquake forces above that level. The ground floor of a three-storey building requires roughly 2–3 times the bracing of the top storey.
• Timber shear walls: Continuous wall panels from foundation to roof, sheathed and nailed as continuous bracing elements. These are the most efficient bracing system for multi-storey timber construction.
• Heavy timber moment frames: Post-and-beam frames with connections designed to resist bending (moment) — possible with heavy timber and pegged joints, but requiring specific engineering design (NZS 3603, not NZS 3604).
• Timber-concrete composite floors: Where concrete is available, a thin concrete topping (40–60 mm) over a timber joist floor increases floor stiffness, provides acoustic separation between storeys, and acts as a fire barrier. This uses modest concrete and no rebar (the concrete topping is unreinforced, relying on shear connectors — which can be coach screws — to the timber joists for composite action).⁴⁹

6.5 Practical multi-storey construction

For the recovery construction programme, two-storey construction should be the standard for urban and peri-urban housing — it is well within NZ building practice, covered by NZS 3604, and constructable with available materials and skills. Three-storey construction should be limited to locations with specific engineering design by qualified structural engineers and should use heavy timber framing methods where possible.

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7. CRITICAL MATERIAL DEPENDENCIES

7.1 Plywood and adhesives

Plywood is the most structurally efficient bracing material available for timber construction. NZ has several plywood and LVL manufacturing plants — Nelson Pine Industries (Richmond), Carter Holt Harvey (Tokoroa), Juken New Zealand (Masterton and Kaitaia).⁵⁰ These plants produce radiata pine plywood and LVL using phenol-formaldehyde (PF) or melamine-urea-formaldehyde (MUF) adhesives.

The adhesive problem: PF resin requires phenol and formaldehyde, both currently imported or produced from imported precursors. NZ does not have a petrochemical industry to produce phenol at scale. Without adhesive, plywood production ceases.

Potential NZ-producible adhesives:

• Casein glue — made from milk protein (casein, extracted from skim milk by acid coagulation) mixed with lime. Casein glue was the standard structural wood adhesive before synthetic resins — it was used extensively in aircraft construction through WWII. It is moisture-resistant when properly formulated (though not waterproof) and provides adequate bond strength for structural plywood. NZ’s dairy industry provides the raw material. The production dependency chain is: skim milk (requiring milk separation, which NZ dairy factories can perform) → acid coagulation (requiring acid — citric, lactic, or hydrochloric) → curd washing and drying → grinding to powder → mixing with slaked lime (requiring limestone calcination, Doc #97) and water. Each step is established chemistry, but scaling from laboratory demonstration to industrial adhesive production sufficient for a plywood plant requires process control, drying facilities, and consistent raw material supply that will take months to establish.⁵¹
• Blood albumin glue — bovine blood, collected during destocking slaughter (Doc #47), can be processed into a protein-based adhesive by heat-coagulating the blood protein fraction and mixing with lime. Less well-characterised than casein for structural applications and typically lower in bond strength and water resistance. Used historically in plywood production (particularly in the US Pacific Northwest, 1920s–1940s) but largely abandoned when synthetic resins became available due to inferior durability and odour issues. A fallback option if casein supply is insufficient, not a first-choice adhesive.
• Tannin-formaldehyde — pine bark tannins (abundant from NZ radiata pine debarking) can partially replace phenol in PF-type adhesives. If formaldehyde supply exists (producible from methanol via catalytic oxidation — methanol can be obtained by wood distillation, Doc #111, or methane reforming), tannin-formaldehyde adhesives are a viable route to structural plywood production. However, tannin-formaldehyde adhesives typically achieve 70–90% of the bond strength of conventional PF resins, and the formulation requires careful optimisation for each tannin source — this is not a drop-in replacement.⁵²

Assessment: Plywood production can probably continue using NZ-sourced adhesives, but transitioning requires development, testing, and qualification — a process likely requiring 12–24 months from initiation to validated production runs, based on historical precedent with casein adhesive development.⁵³ Casein glue is moisture-resistant but not waterproof; plywood produced with casein adhesive is suitable for interior structural use and sheltered exterior applications but will delaminate under prolonged water exposure — a meaningful performance gap compared to PF-bonded plywood, which is rated for full weather exposure.⁵⁴ This should begin during Phase 1 so that adhesive supply does not become the binding constraint on plywood production.

7.2 Roofing

NZ houses are predominantly roofed with profiled steel sheet (Colorsteel/Colorcote) produced by NZ Steel at Glenbrook or by coating operations using Glenbrook base steel.⁵⁵ This steel roofing is lightweight, durable, fire-resistant, and well-suited to NZ conditions. Domestic production can continue as long as Glenbrook operates (Doc #89).

Alternative roofing materials:

• Timber shingles — split or sawn from durable timber (macrocarpa, Douglas fir heartwood). Labour-intensive to produce but a proven roofing material used in NZ historically and currently for some heritage and premium buildings. Expected service life: 20–40 years depending on species, exposure, and maintenance.⁵⁶
• Corrugated iron from recycled steel — existing stocks of corrugated iron from demolished buildings can be reclaimed, straightened, and reused.
• Thatch — raupō (bulrush), toetoe, or straw thatch is a traditional roofing material in NZ Māori and Pacific building. Requires steep pitch (45+ degrees), regular replacement (5–15 years), and presents a fire hazard. A last-resort option but functional.⁵⁷

7.3 Window glass

NZ has no float glass manufacturing. Existing glass stocks are finite. Doc #98 addresses glass production possibilities from NZ sand. Under recovery conditions, window sizes should be minimised where possible (reducing heat loss — Doc #98 — and glass demand), salvaged glass should be recovered from demolished buildings, and window openings in new construction should be sized for standard salvaged glass dimensions where practical.

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8. WORKFORCE TRAINING

8.1 Existing workforce

NZ has approximately 60,000–80,000 people employed in residential construction, including carpenters, builders, building inspectors, and related trades.⁵⁸ This is one of NZ’s largest skilled workforces and a critical recovery asset. Most NZ builders are trained in modern methods — power tools, proprietary fasteners, engineered products. Retraining for recovery conditions involves additions to their existing skill set, not replacement of it.

8.2 Training priorities

1. Timber grading — visual stress grading of structural timber to NZS 3631. Currently performed primarily at sawmills by trained graders. Under recovery conditions with more distributed milling (Doc #99, Section 6), grading capability must be more widespread. Training: 2–5 days for an experienced builder to learn visual grading principles.⁵⁹

2. Traditional joinery — mortise-and-tenon, pegged joints, housed joints, half-laps. Most NZ builders have not cut these joints since (if ever) their apprenticeship. Training: 2–4 weeks of practical workshop instruction for competent hand and power tool joinery. Heritage builders (Doc #159) and experienced boat builders (Doc #159) are the primary source of teaching expertise.

3. Seismic bracing with non-standard materials — board sheathing, diagonal bracing, and their correct nailing patterns. Structural engineers must develop and distribute the design tables; builders must learn the installation requirements. Training: 1–2 days of instruction, supplemented by printed guides at every building site.

4. Timber pile foundations — layout, excavation, pile placement, bearer connection, and seismic bracing of pile foundations. This is an older NZ skill that has largely been replaced by concrete slab construction. Training: 2–5 days practical instruction.

5. Hand tool skills — as power tool consumables (saw blades, drill bits, sanding discs) deplete, hand tool competence becomes increasingly important. Hand sawing, chiselling, planing, boring, and sharpening are learnable skills that increase builder independence from manufactured consumables. Training: ongoing, integrated into general construction practice.

8.3 Training delivery

• Polytechnics and ITOs (Doc #157) — formal training programmes for new entrants and retraining for existing builders.
• On-site mentoring — experienced builders teaching apprentices and less experienced workers during actual construction. This is how most building skill has historically been transmitted in NZ.
• Printed building guides — recovery-adapted versions of NZ building guidance, distributed to every construction site. These must include: span tables, nailing schedules, bracing requirements by zone, connection details for traditional joinery, foundation details for timber piles, and a seismic zone map.
• Heritage skills preservation (Doc #160) — identify and engage the small number of NZ builders who retain traditional timber joinery skills. Some heritage builders, boat builders, and restoration specialists work in these methods daily. Their knowledge is the seed for wider training.

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9. CRITICAL UNCERTAINTIES

Uncertainty	Impact if unfavourable	Mitigation
Fastener stocks and depletion rate	If nail/bolt stocks deplete faster than domestic production scales up, construction programme slows	National inventory (Recommended Action #2); accelerate Doc #105 wire-to-nail production
Plywood adhesive supply	If imported adhesive runs out before NZ alternatives are developed, plywood production ceases and bracing strategy must shift entirely to board sheathing	Begin adhesive R&D immediately (Recommended Action #8); stockpile plywood for bracing use
Seismic event during recovery	A major earthquake in a high-seismic-zone city (Wellington, Christchurch, Napier) would damage or destroy thousands of buildings, creating construction demand potentially exceeding 10,000–20,000 dwellings in a single event while the system is already stretched	Cannot be prevented; ensure all new construction meets seismic requirements; pre-position timber stocks; maintain construction workforce readiness
Nuclear winter effect on timber growth	30–60% growth reduction (Doc #1, Section 8) reduces long-term timber supply, though NZ’s existing standing stock of approximately 500–600 million m³ provides a large buffer60	Standing stock provides decades of buffer; nuclear winter growth reduction does not affect short-to-medium-term supply
Builder workforce availability	Competition from agriculture, infrastructure, and other recovery demands may reduce construction workforce below needs	Construction provides essential health and productivity benefits (Section: Economic Justification); prioritise housing in workforce allocation
Quality of recovery-era construction	Pressure to build quickly may compromise structural quality, especially seismic detailing — consequences deferred until the next earthquake	Maintain inspection requirements; emphasise connection quality over speed; printed guides at every site
Timber treatment depletion	As CCA/boron stocks run out, untreated or alternatively treated timber in exposed and ground-contact applications may fail prematurely	Design for replaceability — piles and bearers should be accessible for replacement; use naturally durable species for critical durability applications
Ground conditions at construction sites	Liquefaction risk, soft soils, and slope instability are site-specific and require geotechnical knowledge that may be in short supply	Use published liquefaction and ground condition maps; avoid known problem sites; train builders in basic ground assessment

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10. CROSS-REFERENCES

Document	Relationship
Doc #156 — Skills Census	Construction workforce inventory; builder skills; portable sawmill locations
Doc #60 — Road and Bridge Maintenance	Timber bridge construction (shared heavy timber techniques); route access for timber transport
Doc #89 — NZ Steel: Glenbrook Operations	Steel supply for roofing, nails, bolts; wire rod for fastener production
Doc #91 — Machine Shop Operations	Bolt threading; hardware fabrication; tool repair
Doc #92 — Blacksmithing	Custom hardware fabrication; hinge, latch, and bracket production
Doc #97 — Cement and Concrete	Concrete for foundation pads; complementary material for foundations and floors
Doc #98 — Glass Production	Window glass supply for new construction
Doc #99 — Timber Processing and Sawmilling	Timber supply chain; species properties; preservation methods; portable sawmills
Doc #100 — Harakeke Fiber	Potential fiber reinforcement for concrete; lashing material for temporary structures
Doc #102 — Charcoal Production	Pine tar for timber preservation; charcoal for blacksmithing (hardware production)
Doc #105 — Wire, Fencing, and Nails	Nail and wire production from NZ steel — critical fastener supply
Doc #141 — Wooden Boatbuilding	Shared timber joinery knowledge; species selection; adhesive development
Doc #145 — Workforce Reallocation	Labour allocation to construction programme
Doc #145 — Treaty and Māori Governance	Partnership requirements for any native timber access
Doc #157 — Trade Training Priorities	Builder training pipeline; polytechnic programmes
Doc #160 — Heritage Skills	Traditional joinery knowledge; hand tool skills; timber grading expertise
Doc #163 — Housing Insulation Retrofit	Complementary document — insulation and construction are twin programmes

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FOOTNOTES

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1. Canterbury earthquake building damage: Canterbury Earthquakes Royal Commission, Final Report (2012). Approximately 10,000 residential properties in greater Christchurch were “red-zoned” (land damage too severe for economical repair). Approximately 50% of CBD buildings were demolished. Timber-framed residential buildings performed significantly better structurally than unreinforced masonry and concrete frame buildings. https://canterbury.royalcommission.govt.nz/↩︎

2. NZ plantation forest estate: Ministry for Primary Industries, National Exotic Forest Description (NEFD) reporting series. Approximately 1.72 million hectares, ~90% radiata pine. Standing volume approximately 500–600 million cubic metres. See Doc #99 for detailed forestry data. https://www.mpi.govt.nz/forestry/↩︎

3. NZ construction workforce: Stats NZ, Business Demographics statistics; MBIE construction sector reports. The residential construction workforce includes carpenters and joiners (~30,000), other building trades (~15,000–20,000), and related occupations (inspectors, designers, project managers). Total residential construction employment fluctuates with the building cycle. The figures cited are approximate. https://www.stats.govt.nz/↩︎

4. NZS 3604:2011, Timber-Framed Buildings. Published by Standards NZ. This is the prescriptive standard governing the design and construction of timber-framed residential buildings in NZ up to three storeys. It provides span tables, bracing requirements, connection details, and foundation design for standard residential construction. It is the most widely used structural standard in NZ building. https://www.standards.govt.nz/↩︎

5. Māori building traditions: Best, E. (1924), “The Maori House and its Interior,” Government Printer, Wellington; also Mead, H.M. and Grove, N. (2001), “Nga Pepeha a nga Tipuna.” Contemporary wharenui construction retains traditional framing and joinery knowledge — large-section timber frames with notched, pegged, and lashed connections. This knowledge is held by Māori carvers (tohunga whakairo) and builders and has direct practical application to heavy timber construction.↩︎

6. NZ housing shortage: Various estimates. MBIE estimated a housing shortfall of approximately 40,000 dwellings nationally as of 2020, concentrated in Auckland. Other estimates range from 20,000 to 60,000 depending on methodology and definition of adequacy. See: MBIE, “Residential Building Activity” reports; NZ Productivity Commission, “Housing Affordability” inquiry (2012). https://www.mbie.govt.nz/↩︎

7. NZ dwelling construction rates: Stats NZ, Building Consents Issued. NZ issued building consents for approximately 35,000–50,000 new dwellings per year in the early 2020s (a historically high period driven by the housing shortage and immigration). The long-term average is lower. https://www.stats.govt.nz/↩︎

8. Construction labour hours: Estimates based on NZ building industry data and quantity surveying references. A standard 3-bedroom, single-storey NZ house of approximately 120 m² requires roughly 1,200–2,000 person-hours for full construction (foundations through to lockup and interior finishing). Simpler specifications, experienced crews, and repetitive designs reduce this. These estimates are approximate and vary significantly with design complexity and workforce skill.↩︎

9. NZ construction workforce: Stats NZ, Business Demographics statistics; MBIE construction sector reports. The residential construction workforce includes carpenters and joiners (~30,000), other building trades (~15,000–20,000), and related occupations (inspectors, designers, project managers). Total residential construction employment fluctuates with the building cycle. The figures cited are approximate. https://www.stats.govt.nz/↩︎

10. Material quantities for NZ residential construction: Based on NZ quantity surveying data and standard NZ building practice. Timber volumes, concrete quantities, and fastener weights are approximate for a typical single-storey, 3-bedroom house of approximately 100–120 m². Actual quantities depend on house design, foundation type, and specification level.↩︎

11. NZ domestic sawn timber production: Approximately 4.5–5 million cubic metres per year. Source: MPI forestry statistics. See Doc #99 footnote 4.↩︎

12. NZ plantation forest estate: Ministry for Primary Industries, National Exotic Forest Description (NEFD) reporting series. Approximately 1.72 million hectares, ~90% radiata pine. Standing volume approximately 500–600 million cubic metres. See Doc #99 for detailed forestry data. https://www.mpi.govt.nz/forestry/↩︎

13. Radiata pine structural properties: NZS 3603:1993 (Timber Structures Standard) Table 2.1 specifies characteristic stress values for visually graded NZ radiata pine. SG8 (Stress Grade 8) has characteristic bending strength of 14.0 MPa and lower-bound MOE of 8,000 MPa. SG10 has characteristic bending of 17.7 MPa and MOE of 10,000 MPa. Density values from Walker, J.C.F. (2006), “Primary Wood Processing,” Springer.↩︎

14. Radiata pine structural properties: NZS 3603:1993 (Timber Structures Standard) Table 2.1 specifies characteristic stress values for visually graded NZ radiata pine. SG8 (Stress Grade 8) has characteristic bending strength of 14.0 MPa and lower-bound MOE of 8,000 MPa. SG10 has characteristic bending of 17.7 MPa and MOE of 10,000 MPa. Density values from Walker, J.C.F. (2006), “Primary Wood Processing,” Springer.↩︎

15. NZ plantation forest estate: Ministry for Primary Industries, National Exotic Forest Description (NEFD) reporting series. Approximately 1.72 million hectares, ~90% radiata pine. Standing volume approximately 500–600 million cubic metres. See Doc #99 for detailed forestry data. https://www.mpi.govt.nz/forestry/↩︎

16. Douglas fir structural properties: NZS 3603 and supplementary data from NZ Forest Research Institute (Scion). Douglas fir structural grades have higher characteristic stresses than radiata pine — typically 15–30% higher in bending and stiffness, depending on grade. See also Doc #99, footnote 42.↩︎

17. Macrocarpa in NZ: Macrocarpa heartwood is NZ Durability Class 2 (durable) per NZS 3602. Ground-contact service life of heartwood macrocarpa is commonly cited at 15–25 years, with some in-service examples lasting longer. Macrocarpa is widely planted as shelter belts throughout rural NZ. See: Page, D. and Singh, T. (2014), “Durability of NZ-grown timbers,” NZ Journal of Forestry. See also Doc #99, footnote 41.↩︎

18. Macrocarpa structural properties: Not standardised in NZS 3603 to the same degree as radiata pine. Clear wood bending strength approximately 40–60 MPa; structural grades lower due to knots and defects. MOE approximately 6,000–8,000 MPa. Properties are highly variable depending on growth conditions. Source: NZ timber engineering literature; Scion data.↩︎

19. Native timber construction: See Doc #99 (Timber Processing and Sawmilling), Section 9, for detailed discussion of native timber policy, availability, and the ethical and practical tensions around native harvest. Within this document, Section 1.4 summarises the construction-specific considerations.↩︎

20. Canterbury earthquake building damage: Canterbury Earthquakes Royal Commission, Final Report (2012). Approximately 10,000 residential properties in greater Christchurch were “red-zoned” (land damage too severe for economical repair). Approximately 50% of CBD buildings were demolished. Timber-framed residential buildings performed significantly better structurally than unreinforced masonry and concrete frame buildings. https://canterbury.royalcommission.govt.nz/↩︎

21. Seismic performance of timber connections: The ductility of nailed timber connections is well-documented in earthquake engineering literature. See: Buchanan, A.H. (2007), “Timber Design Guide,” NZ Timber Design Society; Fragiacomo, M. et al., “Seismic response of timber structures,” various publications. The mechanism — nail bending and wood crushing around the nail — absorbs energy without sudden failure.↩︎

22. NZ seismic hazard: NZS 1170.5:2004 (Structural Design Actions — Earthquake Actions), Table 3.3 (Hazard Factor Z). The Z factor represents the peak ground acceleration with a 10% probability of exceedance in 50 years (approximately 500-year return period). Values given in the text are approximate for typical site classes. Actual design values depend on site class and near-fault factors. See: GNS Science, NZ National Seismic Hazard Model.↩︎

23. NZ seismic hazard: NZS 1170.5:2004 (Structural Design Actions — Earthquake Actions), Table 3.3 (Hazard Factor Z). The Z factor represents the peak ground acceleration with a 10% probability of exceedance in 50 years (approximately 500-year return period). Values given in the text are approximate for typical site classes. Actual design values depend on site class and near-fault factors. See: GNS Science, NZ National Seismic Hazard Model.↩︎

24. NZS 3604:2011, Timber-Framed Buildings. Published by Standards NZ. This is the prescriptive standard governing the design and construction of timber-framed residential buildings in NZ up to three storeys. It provides span tables, bracing requirements, connection details, and foundation design for standard residential construction. It is the most widely used structural standard in NZ building. https://www.standards.govt.nz/↩︎

25. NZS 3604 bracing: NZS 3604 Section 5 (Bracing Design) specifies bracing demand calculation and bracing element ratings. Plywood-braced panels are rated at 75–150 BU depending on configuration (panel width, nailing pattern, stud spacing). Bracing demand depends on building mass, plan dimensions, storey height, seismic zone, and wind zone. The values in the text are indicative only — actual design requires reference to the full standard.↩︎

26. Diagonal timber bracing ratings: Let-in diagonal timber braces (100 x 25 mm or 150 x 25 mm let into studs at approximately 45 degrees) are rated at approximately 30–50 BU per brace in NZS 3604. This is significantly less than plywood bracing (75–150 BU per panel), meaning more braces are required for the same total demand.↩︎

27. Board sheathing bracing capacity: Horizontal or diagonal board sheathing (150–200 mm wide boards, 20–25 mm thick, nailed to framing) provides bracing through the shear capacity of the nailed connections. Published test data shows board-sheathed walls provide approximately 30–60% of the racking resistance of equivalent plywood-sheathed walls, depending on board width, thickness, and nailing pattern. See: Buchanan (note 16); historical NZ building research.↩︎

28. NZS 3604 bracing: NZS 3604 Section 5 (Bracing Design) specifies bracing demand calculation and bracing element ratings. Plywood-braced panels are rated at 75–150 BU depending on configuration (panel width, nailing pattern, stud spacing). Bracing demand depends on building mass, plan dimensions, storey height, seismic zone, and wind zone. The values in the text are indicative only — actual design requires reference to the full standard.↩︎

29. NZS 3604 bracing: NZS 3604 Section 5 (Bracing Design) specifies bracing demand calculation and bracing element ratings. Plywood-braced panels are rated at 75–150 BU depending on configuration (panel width, nailing pattern, stud spacing). Bracing demand depends on building mass, plan dimensions, storey height, seismic zone, and wind zone. The values in the text are indicative only — actual design requires reference to the full standard.↩︎

30. Nail consumption per house: Estimates vary with house size and complexity. A typical NZ single-storey 3-bedroom house uses approximately 20,000–40,000 nails of various sizes (framing nails, bracing nails, cladding nails, lining nails). The largest consumers are bracing attachment and interior lining (plasterboard, if used).↩︎

31. NZS 3604 nailing schedules: NZS 3604 Tables throughout the standard specify nail sizes and quantities for all standard connections. The values cited in the text are representative examples — actual construction must follow the full nailing schedules for the specific connection type and loading condition.↩︎

32. Pegged timber construction: Pegged (trunnelled) joints are a traditional timber framing method with a documented history spanning millennia. Modern timber frame construction (particularly in the US “timber frame” tradition) continues to use hardwood pegs as primary fasteners. Structural performance of pegged joints is documented in: Brungraber, R.L. (1985), “Traditional Timber Joinery,” PhD thesis, Stanford University; Schmidt, R.J. and Mackay, R.B. (1997), “Timber Frame Tension Joinery,” University of Wyoming.↩︎

33. Manuka as dowel material: Manuka (Leptospermum scoparium) has a basic density of approximately 650–800 kg/m³ — significantly harder and denser than radiata pine (420–500 kg/m³). It is abundant throughout NZ, growing on marginal and disturbed land, and can be harvested on short rotations. Dowel-sized stems (20–30 mm diameter) are available from young growth. See: Bergin, D. (2011), “Establishment and management of manuka and kanuka plantations,” Tane’s Tree Trust.↩︎

34. Mortise-and-tenon structural performance: The structural capacity of mortise-and-tenon joints is well-characterised in the timber engineering literature. Joint capacity depends on tenon dimensions, peg diameter and number, and timber species. For radiata pine with manuka pegs, typical joint capacities are comparable to bolted connections of similar dimensions. See: Schmidt and Mackay (note 23); Brungraber (note 23); Sobon, J. and Schroeder, R. (1984), “Timber Frame Construction.”↩︎

35. Mortise-and-tenon structural performance: The structural capacity of mortise-and-tenon joints is well-characterised in the timber engineering literature. Joint capacity depends on tenon dimensions, peg diameter and number, and timber species. For radiata pine with manuka pegs, typical joint capacities are comparable to bolted connections of similar dimensions. See: Schmidt and Mackay (note 23); Brungraber (note 23); Sobon, J. and Schroeder, R. (1984), “Timber Frame Construction.”↩︎

36. NZS 3604 nailing schedules: NZS 3604 Tables throughout the standard specify nail sizes and quantities for all standard connections. The values cited in the text are representative examples — actual construction must follow the full nailing schedules for the specific connection type and loading condition.↩︎

37. NZS 3604:2011, Timber-Framed Buildings. Published by Standards NZ. This is the prescriptive standard governing the design and construction of timber-framed residential buildings in NZ up to three storeys. It provides span tables, bracing requirements, connection details, and foundation design for standard residential construction. It is the most widely used structural standard in NZ building. https://www.standards.govt.nz/↩︎

38. NZS 3604:2011, Timber-Framed Buildings. Published by Standards NZ. This is the prescriptive standard governing the design and construction of timber-framed residential buildings in NZ up to three storeys. It provides span tables, bracing requirements, connection details, and foundation design for standard residential construction. It is the most widely used structural standard in NZ building. https://www.standards.govt.nz/↩︎

39. NZS 3604:2011, Timber-Framed Buildings. Published by Standards NZ. This is the prescriptive standard governing the design and construction of timber-framed residential buildings in NZ up to three storeys. It provides span tables, bracing requirements, connection details, and foundation design for standard residential construction. It is the most widely used structural standard in NZ building. https://www.standards.govt.nz/↩︎

40. NZS 3604:2011, Timber-Framed Buildings. Published by Standards NZ. This is the prescriptive standard governing the design and construction of timber-framed residential buildings in NZ up to three storeys. It provides span tables, bracing requirements, connection details, and foundation design for standard residential construction. It is the most widely used structural standard in NZ building. https://www.standards.govt.nz/↩︎

41. NZS 3604:2011, Timber-Framed Buildings. Published by Standards NZ. This is the prescriptive standard governing the design and construction of timber-framed residential buildings in NZ up to three storeys. It provides span tables, bracing requirements, connection details, and foundation design for standard residential construction. It is the most widely used structural standard in NZ building. https://www.standards.govt.nz/↩︎

42. Foundation performance in NZ earthquakes: The Canterbury earthquake sequence (2010–2011) revealed widespread foundation failures — buildings sliding off piles, differential settlement, and liquefaction-induced foundation damage. See: Canterbury Earthquakes Royal Commission (note 1); MBIE guidance on residential foundations post-Canterbury.↩︎

43. Macrocarpa in NZ: Macrocarpa heartwood is NZ Durability Class 2 (durable) per NZS 3602. Ground-contact service life of heartwood macrocarpa is commonly cited at 15–25 years, with some in-service examples lasting longer. Macrocarpa is widely planted as shelter belts throughout rural NZ. See: Page, D. and Singh, T. (2014), “Durability of NZ-grown timbers,” NZ Journal of Forestry. See also Doc #99, footnote 41.↩︎

44. Concrete pad foundations: Small concrete pads as pile supports are a standard NZ foundation detail in NZS 3604. The pad distributes the pile reaction over a larger bearing area and provides a durable interface between the timber pile and the ground. Unreinforced pads are adequate for light residential construction on firm ground.↩︎

45. Liquefaction in Canterbury: Canterbury experienced severe and widespread liquefaction during the September 2010 and February 2011 earthquakes. Liquefaction susceptibility maps have since been developed for Christchurch and other NZ cities. See: Cubrinovski, M. et al. (2011), “Geotechnical aspects of the 22 February 2011 Christchurch earthquake,” Bulletin of the NZ Society for Earthquake Engineering, 44(4); GNS Science liquefaction publications.↩︎

46. Liquefaction in Canterbury: Canterbury experienced severe and widespread liquefaction during the September 2010 and February 2011 earthquakes. Liquefaction susceptibility maps have since been developed for Christchurch and other NZ cities. See: Cubrinovski, M. et al. (2011), “Geotechnical aspects of the 22 February 2011 Christchurch earthquake,” Bulletin of the NZ Society for Earthquake Engineering, 44(4); GNS Science liquefaction publications.↩︎

47. NZS 3604:2011, Timber-Framed Buildings. Published by Standards NZ. This is the prescriptive standard governing the design and construction of timber-framed residential buildings in NZ up to three storeys. It provides span tables, bracing requirements, connection details, and foundation design for standard residential construction. It is the most widely used structural standard in NZ building. https://www.standards.govt.nz/↩︎

48. Fire performance of heavy timber: Large timber sections char at a predictable rate of approximately 0.6–0.8 mm per minute (NZS 3603, clause 3.8; also Buchanan, A.H. (2001), “Structural Design for Fire Safety,” Wiley). A 200 mm x 200 mm post exposed to fire on all four sides retains approximately 160 mm x 160 mm of uncharred cross-section after 30 minutes — still structurally functional. This predictable charring behaviour gives heavy timber better fire performance than unprotected steel (which loses strength rapidly above ~550°C).↩︎

49. Timber-concrete composite floors: The technique involves fixing shear connectors (typically coach screws or notch-and-screw systems) from the timber joists into a thin concrete topping. The composite action increases floor stiffness and acoustic separation. Research and practice in NZ and internationally has demonstrated the effectiveness of this system. See: Yeoh, D. et al. (2011), “State of the art on timber-concrete composite structures,” Journal of Structural Engineering.↩︎

50. NZ plywood and LVL manufacturers: Nelson Pine Industries (Richmond), Carter Holt Harvey (Tokoroa, Marsden Point), and Juken New Zealand (Masterton, Kaitaia) are the main NZ producers of structural plywood and laminated veneer lumber (LVL). Combined output is approximately 300,000–400,000 m³ per year. These plants use phenol-formaldehyde (PF) or melamine-urea-formaldehyde (MUF) adhesives, which are currently imported or produced from imported precursors.↩︎

51. Casein glue: Casein-based adhesives were the standard structural wood adhesive before the development of synthetic resins in the 1940s–1950s. Casein glue was used for structural plywood, glulam, and aircraft construction (including the de Havilland Mosquito, which used casein-bonded plywood extensively during WWII). Casein is extracted from skim milk by acid coagulation, dried, and mixed with hydrated lime and water to form the adhesive. It is moisture-resistant but not fully waterproof — adequate for interior structural applications and sheltered exterior applications. NZ’s dairy industry provides abundant raw material. See: Pizzi, A. (ed.), “Wood Adhesives: Chemistry and Technology,” Marcel Dekker; Forest Products Laboratory (US), “Wood Handbook.”↩︎

52. Tannin-based adhesives: Pine bark tannins can partially replace phenol in phenol-formaldehyde adhesive formulations. Research by Pizzi and others has demonstrated the feasibility of tannin-formaldehyde adhesives for structural plywood production, with performance approaching that of conventional PF resins. NZ radiata pine bark is rich in condensed tannins and is a byproduct of log debarking at sawmills. The remaining challenge is formaldehyde supply — formaldehyde can be produced by catalytic oxidation of methanol, which can itself be produced by wood distillation (Doc #111) or methane reforming. See: Pizzi, A. (2006), “Recent developments in eco-efficient bio-based adhesives for wood bonding,” Journal of Adhesion Science and Technology.↩︎

53. Adhesive development timeline: The transition from laboratory-validated adhesive formulation to consistent industrial-scale production for structural plywood requires process optimisation, bond strength testing to NZ structural plywood standards (AS/NZS 2269), and durability testing. Historical experience with casein adhesives suggests that a motivated development programme with access to dairy feedstock and lime could produce pilot-scale adhesive within 6–12 months and qualify production-scale adhesive within 12–24 months. The timeline depends on availability of analytical equipment for bond testing and on the specific plywood plant’s process requirements. See: Pizzi, A. (ed.), “Wood Adhesives: Chemistry and Technology,” Marcel Dekker; Forest Products Laboratory (US), “Wood Handbook,” Chapter 10 (Adhesives).↩︎

54. Casein glue: Casein-based adhesives were the standard structural wood adhesive before the development of synthetic resins in the 1940s–1950s. Casein glue was used for structural plywood, glulam, and aircraft construction (including the de Havilland Mosquito, which used casein-bonded plywood extensively during WWII). Casein is extracted from skim milk by acid coagulation, dried, and mixed with hydrated lime and water to form the adhesive. It is moisture-resistant but not fully waterproof — adequate for interior structural applications and sheltered exterior applications. NZ’s dairy industry provides abundant raw material. See: Pizzi, A. (ed.), “Wood Adhesives: Chemistry and Technology,” Marcel Dekker; Forest Products Laboratory (US), “Wood Handbook.”↩︎

55. NZ steel roofing: NZ Steel’s Glenbrook works produces coil steel that is roll-formed and coated (zinc and paint coating — Colorsteel brand) for roofing and cladding. This is one of NZ’s most important construction material production capabilities. See Doc #89 for detailed discussion of NZ Steel operations and product range.↩︎

56. Timber shingles: Split or sawn shingles from durable timber species have been used for roofing for centuries worldwide. In NZ, macrocarpa, totara, and heart rimu have been used historically. Service life depends on species, exposure, and installation quality — typically 20–40 years for durable heartwood on a well-ventilated, properly laid roof. Production is labour-intensive (approximately 5–10 person-hours per square metre of roofing from split shingles).↩︎

57. Thatch roofing: Raupō (bulrush, Typha orientalis) was the primary roofing material for traditional Māori whare. Thatch requires a steep pitch (typically 45 degrees or more) to shed water, requires periodic replacement (every 5–15 years), and is a fire hazard. It is a functional roofing material of last resort where other options are unavailable. See: Best, E. (1924), cited at note 5.↩︎

58. NZ construction workforce: Stats NZ, Business Demographics statistics; MBIE construction sector reports. The residential construction workforce includes carpenters and joiners (~30,000), other building trades (~15,000–20,000), and related occupations (inspectors, designers, project managers). Total residential construction employment fluctuates with the building cycle. The figures cited are approximate. https://www.stats.govt.nz/↩︎

59. Timber grading training: Visual stress grading of structural timber to NZS 3631 (NZ Timber Grading Rules) involves assessing each piece of timber for knots, slope of grain, wane, distortion, and other features that affect structural performance. Training for experienced builders typically takes 2–5 days of instruction and supervised practice. NZ currently has a cadre of trained graders at major sawmills; this capability must be expanded under recovery conditions. See: NZS 3631:1993 (NZ Timber Grading Rules); Scion timber grading training materials.↩︎

60. NZ plantation forest estate: Ministry for Primary Industries, National Exotic Forest Description (NEFD) reporting series. Approximately 1.72 million hectares, ~90% radiata pine. Standing volume approximately 500–600 million cubic metres. See Doc #99 for detailed forestry data. https://www.mpi.govt.nz/forestry/↩︎