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13 June 2011

DBH's Simpler System for Structural Timber Framing

The changes, which are contained in an amendment to the Building Code Acceptable Solution B2/AS1, mean that now a single class of timber treatment, H1.2, can be used for all enclosed radiata pine and Douglas fir framing.

“The new system offers potential cost savings by simplifying inventories and reducing the likelihood of mistakes that can lead to rework. It is expected to make the consent and inspection process more straightforward,” says the Department’s Chief Engineer Mike Stannard.

“Previously there were as many as four different classes of timber, including untreated timber, which could be used to frame a building. This was unnecessarily complex,” he says.

The exception to the new single treatment class is cantilevered deck joists and framing which need H3.2 treatment level, the same level of treatment as timber that is exposed to weather. Framing choices for timber other than radiata and Douglas fir remain unchanged.

“Cantilevered decks depend on a single point of support and there is less chance that leaks will be discovered and repaired; this indicates a need for a higher level of treatment,” says Mr Stannard.

The H1.2 treatment class has boron treatment. Recent scientific research has shown that, for framing timber, H1.2 boron provides protection against fungal decay comparable to LOSP H3.1. The changes do not compromise existing levels of protection for building owners.

The changes also:

  • remove the necessary use of solvent based treatments for framing
  • provide an option for boron treated claddings and cavity battens
  • introduce an option for the use of untreated Douglas fir framing for low-risk designs that meet specific conditions.

The changes follow years of work with the sector and a consultation process which resulted in almost 240 submissions, with strong support for the proposed changes.

The new Acceptable Solution came into effect on 4 April 2011. The previous system can still be used until 30 June 2011, allowing a transition period for industry.

The revised Acceptable Solution is now available in the B2 Durability Compliance Document on the Department’s website at.

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