Treated Timber Changes

Treated Timber Changes

Higher levels of timber treatment will be required in parts of buildings more at risk from leaking, the Building Industry Authority announced today.

However final changes to its Acceptable Solution , that sets out the level of treatment required of timber, are less conservative than the original proposals issued in June, Authority chairman Barry Brown said.

“The changes are more flexible and are based on assessing the risk of moisture causing damage in specific parts of a building and the level of protection needed to manage that risk,” Mr Brown said.

“They will require additional treatment levels in some situations, but we are not introducing a requirement that all framing timber is treated as was proposed earlier this year.

“Our focus has been on putting in place a regime that will provide homeowners and users with appropriate protection if a building leaks. We have also taken into account feedback from the timber and building industries during our extensive consultation on this matter.”

“This approach is about putting additional protection in place where it is needed. It also means that certain timber products - like untreated kiln dried radiata pine and untreated Douglas fir - can still be extensively used in buildings built to the Acceptable Solution.”

Key Points Key elements of the Acceptable Solution change include: An increase in treatment level from H1 (provides insect only resistance) to H1.2 (insect plus fungal or rot resistance) for: subfloor framing exterior wall framing including parapets (except in certain low risk brick veneer buildings) enclosed framing and structural supports for riskier roof types (like enclosed skillion roofs) An increase in treatment level from H1 to H3.1 for all framing and boundary joists or walls for enclosed decks, balconies and balustrades, and for enclosed flat roofs. Untreated kiln dried radiata and untreated Douglas fir can still be used in a range of situations including: roof framing, trusses and ceiling joists, except certain roof types with a higher risk of leaking and causing damage (like flat roofs) inter-storey floor joists interior wall framing, beams, rafters and joists exterior wall framing in single storey, low risk brick veneer buildings New requirements for colour coding and identification marking of timber will be introduced so that treatment level and treatment type will be more easily identified. The changes apply to all buildings, not just to residential buildings as originally proposed.

The changes have been the subject of an independent cost benefit analysis by the New Zealand Institute of Economic Research. This shows that, when combined with the proposed changes to the external moisture requirements, they will result in a national economic benefit of between $94 million and $1.1 billion over the next 25 years .

The BIA estimates the timber treatment changes will add around $500 to the cost of building an average house.

The changes are proposed to take effect from 1 April 2004, subject to feedback from the industry over implementation timing.

Mr Brown said the changes to B2/AS1 were about how a building copes if it leaks.

“Treated timber is a second line of defence. That is, it can resist decay for a period of time while the moisture dries, or it gives you time to discover and fix a leak before too much damage is done."

The changes to B2/AS1 have been developed in tandem with changes to the Acceptable Solution E2/AS1 that deals with the way external moisture should be managed in buildings – that is, how water is kept out or coped with by, for example, cladding systems, flashings and wall cavities. E2/AS1 is due to be issued early in 2004.

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