Specialty Timbers New Zealand

Durability and the building code

NZS 3602:2003 Timber and wood based products for buildings is the durabilityThe building code compliance document is clause B2, which states that the durability performance of the timber building component must meet the life intended for the building. Acceptable Solution for building components produced from timber. The standard covers the materials themselves and aspects of design and construction that are relevant to their performance in use.

Naturally durable timber species and the building components they can be used for are listed in the tables below. For species not listed here go to Alternative Solutions for durability

NZS 3602:2003

Building components that are required to last for a minimum of 50 years (e.g. structural components) are listed in Table 1.

Building components that are required to last for a minimum of 15 years (e.g. cladding and decking) are listed in Table 2.

Content in blue © Copyright Standards New Zealand 2011. The following content from NZS 3602:2003 has been reproduced with permission from Standards New Zealand under Copyright License 000883. Ensure you refer to the full standard - available at no cost from the Standards New Zealand website. NZS 3602 specifies further requirements such as grades and in-service moisture range. Applicable figures and clauses are available in NZS 3602.

Wood-based building components made from wood species other than those listed may also achieve the required durability but there is not enough data on their durability to permit their inclusion in this standard.* Note 1, Table 1

Table 1 - Requirements for solid timber to achieve a (minimum) 50 year durability performance
NZS 3602 Ref No.	Wood-based building components	Species or type	Level of treatment⁽²⁾ to NZS 3640
C – Members protected from the weather but exposed to ground atmosphere (see section 108 of NZS 3602)
1C.1	Jackstuds, subfloor braces, bearers, wall plates, floor joists to the subfloor, blocking, subfloor wall studs, wailings and battens, wall studs and nogs, diagonal boards	Larch Cypress⁽⁶⁾ sapwood Cypress⁽⁶⁾ heartwood	None H1.2 None
1C.3	Interior flooring, suspended ground floors	Cypress⁽⁶⁾ heartwood Cypress⁽⁶⁾ sapwood Matai heartwood Matai sapwood Rimu heartwood Rimu sapwood All Eucalyptus species Tawa	None H1.1 None H1.1 None H1.1 None H1.1
D – Members protected from the weather but with a risk of moisture penetration conducive to decay (see section 109 of NZS 3602)
Roof members (in or associated with)
1D.1	Sarking and framing not protected from solar driven moisture through absorbent cladding materials⁽⁸⁾	Larch Cypress⁽⁶⁾ heartwood Cypress⁽⁶⁾ sapwood	None None H1.2
1D.3	Enclosed skillion roof framing and associated roof members	Larch Cypress⁽⁶⁾ heartwood Cypress⁽⁶⁾ sapwood	None None H1.2
1D.4	Valley boards and boards supporting flashings or box gutters and flashings to roof penetrations and upstands to roof decks⁽¹⁰⁾	Larch Cypress⁽⁶⁾ heartwood Cypress⁽⁶⁾ sapwood	None None H1.2
Wall members (in or associated with)
1D.5	Framing and other members within or beneath a parapet except in situations detailed in 1D.13 (i.e. Framing and other members in exterior walls including boundary joists, where monolithic claddings are fixed directly to the framing and do not comply with E2/AS1)	Larch Cypress⁽⁶⁾ heartwood Cypress⁽⁶⁾ sapwood	None None H1.2
1D.6	Framing and other members within enclosed decks or balconies⁽⁹⁾ (See figure 1 NZS 3602)	Larch Cypress⁽⁶⁾ heartwood Cypress⁽⁶⁾ sapwood	None None H1.2
1D.7	Framing and other members supporting enclosed decks or balconies where failure is potentially life threatening, such as when the support is enclosed post and beam construction	Larch Cypress⁽⁶⁾ heartwood Cypress⁽⁶⁾ sapwood	None None H1.2
E – Members not exposed to weather or ground atmosphere and in dry conditions (see section 110 of NZS 3602)
1E.1	All roof trusses, including gable end trusses, roof framing, ceiling and eaves framing, purlins and battens excluding skillion roof framing, and sarking described in 1D.1	Larch Cypress heartwood Cypress sapwood	None None H1.1
1E.2	All midfloor framing excluding boundary joists but including associated ceiling framing	Larch Cypress heartwood Cypress sapwood	None None H1.1
1E.3	Unlined buildings except those not allowed in 110.2(f) of NZS 3602	Larch Cypress heartwood Cypress sapwood	None None H1.1
1E.4	Timber framing (including boundary joists) in exterior walls clad with masonry veneer complying to SNZ HB 4236 on a single storeyed building but with restrictions set out in 110.2(b) and in figure 3 of NZS 3602	Larch Cypress heartwood Cypress sapwood	None None H1.1
1E.5	Internal walls excluding those supporting decks and balconies	Larch Cypress heartwood Cypress sapwood	None None H1.1
1E.7	Interior flooring	Cypress heartwood Cypress sapwood Matai heartwood Matai sapwood Rimu heartwood Rimu sapwood Beech heartwood Beech sapwood Eucalyptus heartwood Eucalyptus sapwood Tawa	None H1.1 None H1.1 None H1.1 None H1.1 None H1.1 H1.1

NOTE (2) Throughout Table 1, timber treated to a higher level than the minimum satisfies the minimum requirements. (5) H3.2 refers to preservative treatments outlined in NZS 3640. (6) Cypress species include Cupressus macrocarpa (macrocarpa), C. lusitanica (Mexican cypress) and Chamaecyparis lawsoniana (Lawson's cypress). Refer to AS/NZS 1148. (8) Timber shakes and shingles, and similar absorbent claddings, absorb moisture that can be driven in frame cavities by evaporation. Unless the cavities are adequately drained and ventilate, continuing condensation caused by solar driven transfer increases the moisture content in the cavities and timber framing requiring a higher level of timber treatment to resist decay. (9) Such as joists, lintels, wall plate and double top plates, studs, together with parapets, enclosed balustrades, boxed columns and chimneys. (10) Any metal flashing shall be separated from the treated timber with building paper. (11) Exposed ends of joists shall be protected by a boundary joist. (12) Refer to table 1 row 1E.4 NZS 3602.

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Table 2 - Requirements for solid timber to achieve a 15-year durability performance
NZS 3602 Ref No.	Wood-based building components	Species or type	Level of treatment
A - Members exposed to exterior weather conditions and dampness (see section 111 of NZS 3602)
2A.1 2A.2 2A.3	Weatherboards Base battens Fascia, barge and coverboards	Larch heartwood Cypress⁽⁴⁾ heartwood Redwood heartwood Western red cedar heartwood	None None None None
2A.5 2A.6	Exterior joinery, including window frames, sills, and sashes, exterior door frames, sills and doors Timber reveals for aluminium windows	Redwood heartwood Western red cedar heartwood Cypress⁽⁴⁾ heartwood	None None None
2A.7	External stairs, stair handrails and balustrades, verandah floors, unroofed decking (which can easily be replaced)	Cypress⁽⁴⁾ heartwood Rimu heartwood Eucalyptus⁽⁶⁾ heartwood Beech heartwood (silver, red, hard)	None None None None
B – Members protected from the weather and dampness (see section 111 of NZS 3602)
2B.1	Non-load bearing interior wall framing	Larch Cypress⁽⁴⁾ heartwood	None None
2B.2	Stair treads, risers and handrails	Larch Cypress⁽⁴⁾ Rimu Eucalyptus⁽⁶⁾ Beech - silver, red, hard Tawa	None None None None None None
NOTE (2) Throughout Table 2, timber treated to a higher level than the minimum satisfies the minimum requirements. (4) Cypress species include Cupressus macrocarpa (macrocarpa), C. lusitanica (Mexican cypress) and Chamaecyparis lawsoniana (Lawson's cypress). Refer to AS/NZS 1148. (6) Eucalyptus species include E. botryoides, E. saligna, E. globoidea, E. obliqua, E. pilularis.

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Durability and the building code

NZS 3602:2003

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