Farm Forestry timbers - NZS 3602 Durability

NZS 3602 Durability

NZS 3602:2003 Timber and wood based products for buildings covers N.Z. building code durability requirementsTo meet durability requirements of the New Zealand building code, timber building elements must comply with Compliance Document B2 Durability. Acceptable Solution B2/AS1 references NZS 3602 Timber and wood based products for buildings. for timber and wood-based products. The durability performance of the timber building component must meet the life intended for the building. The standard covers the materials themselves and aspects of design and construction that are relevant to their performance in use.

Timber species and required levels of treatment which comply with the durability requirement are listed below (Table 1 and Table 2) for a range of wood-based building components.

The building code

From N.Z. Building Code Clause B2 Durability Acceptable Solution for B2/AS1:

"For information on species (other than radiata pine and Douglas fir) which can be used for timber building elements under this Acceptable Solution, consult NZS 3602:2003 table 1(See below) and table 2(See below) (for structural uses) and table 3 (for non-structural uses)."

"Where treatment is required, the minimum Hazard Class

Hazard classes
H1.1	Timber used in situations protected from the weather, dry in service and where resistance to borer only is required.
H1.2	Timber used in situations protected from the weather but where there is a risk of moisture exposure conducive to decay.
H3.1	Timber used outdoors above ground, exposed to the weather – generally in non-structural applications; i.e. fascia boards, weatherboards.
H3.2	Timber used outdoors above ground, exposed to weather or protected from the weather but with a risk of water entrapment; i.e. structural applications, decking, fencing and pergolas.

as per NZS 3640 (round and sawn timber) or AS/NZS 1604 (Part 3 for plywood and Part 5 for laminated beams and posts) is specified."

"The use of different timbers or timber treatments to those referred to in NZS 3602 are outside the scope of this Acceptable
Solution.*Amendment 7, effective 4 April 2011, to the Compliance Document for Clause B2 Durability of the New Zealand Building Code. Where the use of a different timber or timber treatment is proposed, it shall be separately assessed for compliance with the Building Code*Amendment 7, effective 4 April 2011, to the Compliance Document for Clause B2 Durability of the New Zealand Building Code.. For example, if imported hard-wood is to be used to surface a deck, evidence that the timber was durable for a minimum of 15 years in the expected exposure conditions is required."

Determinations

The Department of Building and Housing and its predecessor, the Building Industry Authority (Now MBIE, Ministry for Building and Innovation) issued six determinations about the use of macrocarpa or cypress timbers in buildings. In all six cases, the question was whether these timbers, as installed, complied with Building Code Clause B2 Durability.

The six determinations have established certain criteria to decide whether macrocarpa, or Lawson or Mexican cypress timbers, are Code-compliant when installed to the exterior of buildings. Such timbers are the equivalent to structural-grade radiata pine treated to Hazard Class H3.2, and therefore comply with Clause B2 (they have a durability of at least 50 years according to Clause B2.3.1 (a)(i)) of the Building Code if:

they are heart timbers
they are not in contact with the ground
they are relatively easy to replace
their surfaces are treated with an appropriate preservative
their cut ends are similarly treated or suitably capped

MBIE can initiate a determination where it believes it is necessary to achieve the aims of the Building Act.

NZS 3602:2003

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 to purchase from the Standards New Zealand website.

The following tables provide timber species listed and level of treatment required (if any) for a range of wood-based building components. NZS 3602 specifies further requirements such as grades and in-service moisture range. Applicable figures and clauses are available in NZS 3602. Note: 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
1D.8	Framing and other members supporting enclosed decks or balconies⁽⁹⁾ (See figure 1 NZS 3602)	Radiata pine and Douglas fir	H1.2
1D.14	All other exterior wall framing and other members including exterior and boundary joists^(9)(11) except those clad in masonry veneer covereed by 110.2(c) NZS 3602⁽¹²⁾	Radiata pine and Douglas fir	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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NZS 3640 Timber treatment Standard

Content in blue © Copyright Standards New Zealand 2011. Content from NZS 3640:2003 has been reproduced with permission from Standards New Zealand under Copyright License 000883. For full details, please refer to NZS 3640:2003 available to purchase from the Standards New Zealand website.

1.1.2*(Scope)

The requirements for hazard class H1.1 and H1.2 apply to all species for which hazard class H1.1 and H1.2 is specified in NZS 3602. Hazard classes H2, H3.1, H3.2, H4, H5 and H6 apply only to Pinus species.

Note: For more information about Hazard Classes

Hazard classes
H1.1	Timber used in situations protected from the weather, dry in service and where resistance to borer only is required.
H1.2	Timber used in situations protected from the weather but where there is a risk of moisture exposure conducive to decay.
H3.1	Timber used outdoors above ground, exposed to the weather – generally in non-structural applications; i.e. fascia boards, weatherboards.
H3.2	Timber used outdoors above ground, exposed to weather or protected from the weather but with a risk of water entrapment; i.e. structural applications, decking, fencing and pergolas.

download NZ Hazard Class and Timber Treatment Summary Table from the NZ Wood website.

C1.1.2

While it may be possible to treat other species using the provisions of this Standard, such treatments are outside the scope of this Standard and the adequacy of the resulting treatments will need to be demonstrated.

For the treatment of hardwoods refer to AS 1604.1. For the treatment of other wood-based products, refer to AS/NZS 1604, Parts 2 to 5.

AS/NZS 1604 Specification for Preservative Treatment

Content in blue © Copyright Standards New Zealand 2011. Content from AS/NZS 1604 has been reproduced with permission from Standards New Zealand under Copyright License 000883. For full details, please refer to AS/NZS 1604 available to purchase from the Standards New Zealand website.

1.9*Scope Use in New Zealand

When used in New Zealand in situations where treatment to hazard class H1.1, H1.2, H3.1 or H3.2 is required as specified in the New Zealand Building Code and in NZS 3602, Reconstituted wood productPart 2, PlywoodPart 3, LVLPart 4, Glue laminated timber productPart 5, shall be treated to the preservative retentions for H1.1, H1.2, H3.1 or H3.2 as set out in NZS 3640. Preservative penetration shall be in accordance with this Standard.

Radiata pine and Douglas fir

NZS 3602:2003 also specifies the requirements for timber treatment of radiata pine and Douglas fir in buildings. However, changes to the hazard class requirements for radiata pine and Douglas fir timber used within the building envelope were cited into the Clause B2 of the Building Code on 1 July 2011. This means that the minimum H1.2 hazard class requirements is now fully effective for radiata pine and Douglas fir timber framing in buildings, where it is protected from the weather (i.e. enclosed timber framing). There are exceptions to this requirement such as allowance for untreated Douglas fir to be used in houses of simple design and also an H3.2 requirement for cantilevered deck joists. Consult the tables in A QUICK GUIDE TO Timber Treatment for Enclosed Framing, Published in April 2011 by Department of Building and Housing for the few exceptions to H1.2 treatment. For other species of wood and engineered wood products (such as LVL and Glulam), the Acceptable Solution does not change.

Disclaimer: While every effort is made to ensure the accuracy of the information provided on this site, Farm Forestry Timbers Society do not accept liability for any consequences arising from reliance on the information published. If readers have any doubts about acting on any articles they should seek confirming, professional advice.

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