Timber treatment for enclosed framing - new guidelines in place by 1 July 2011

Written by building4u on Wednesday, 06 July 2011 11:40 in Building Code Updates
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Treated Timber Treated Timber

The Department of Building and Housing has implemented a new Acceptable Solution standard (amendment 7 to the B2/AS1 code), effective from 1 July 2011, for the purposes of demonstrating compliance with the Building Code (and more specificaly with Clause B2 - the technical clause covering durability). This standard relates to treated timber (radiata pine and Douglas fir) used for enclosed framing. For other wood species and engineered wood products the Acceptable Solution does not change (see Accpetable Solution NZS 3602:2003 Tables 1 and 2 on the DBH website for more details).

Why do you need to know this and comply?

Timber must be adequately protected against fungal and insect attack damage, in order to comply with the Building Code and to be durable - the new system improves protection levels.

Following the B2/AS1 DBH guidelines demostrates your compliance with the Building Code

Low-risk housing does not need to comply with this standard - see below for conditions

NB There are ways of complying with the Building Code other than via the Acceptable Solution - often referred to as alternative solutions see the following web site for more information: http://www.dbh.govt.nz/blc-alternative-solutions

Untreated solid Douglas fir framing can be used for a house of no more than two storeys (as defined in NZS 3604), that is designed and constructed to NZS 3604, if ALL the following low-risk conditions are met:

Low-risk house conditions

    • is a standalone, single household unit of no more than two storeys (as defined in NZS 3604), that is designed and constructed to NZS 3604

and

    • is situated in wind zones no greater than 'high' as defined in NZS 3604

and

    • has a building envelope complexity no greater than 'medium risk', and a deck design no greater than 'low risk', as defined by the risk matrix in the Acceptable Solution E2/AS1

and

    • has drained and vented cavities complying with E2/AS1, behind all claddings

and

    • uses roof and wall cladding systems and details meeting E2/AS1

and

    • has a risk matrix score of no more than 6 on any external wall face, as defined in E2/AS1

and

    • has a simple pitched roof with hips, valleys, gables, or mono pitches, all draining directly to external gutters*

and

    • has a roof slope of 10° or more

and

    • if it has a skillion roof, the roofing material is corrugated iron or concrete, metal or clay tiles for adequate ventilation

and

    • has eaves 450mm-wide or more for single-storey houses, and eaves 600mm-wide or more for two-storey houses.

 

* The roof does not have internal or secret gutters, concealed gutters behind fascias, or any roof element finishing within the boundaries formed by exterior walls (eg, the lower ends of apron flashings, chimneys, dormers, clerestories, box windows).

H1.2 indicates boron treated timber which is coloured pink -read on to find out more about for Health and Safety issues related to boron treatment

Health and Safety

Timber treatments consist of chemicals that may be harmful. Important measures to take when using treated timber are:

    • reduce contact by wearing gloves, goggles and a dust mask
    • don't burn off-cuts or cook with them
    • dispose of waste in an approved landfill
    • wash your hands before using the toilet, smoking or eating
    • wash work clothes separately
    • ventilate work spaces as much as you can
    • working with solvent damp timber is not advised, solvent damp timber should be allowed to properly dry off before use

 

 

 

Last modified on Thursday, 10 November 2011 14:03
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