Summary of key issues from the consultation on Timber treatment changes - March 2011
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What are the proposed changes?
The changes introduce a single treatment class for nearly all enclosed timber framing by amendment to the Acceptable Solution B2/AS1.
- H1.2 treatment is to be used for nearly all enclosed timber framing. This includes internal walls and roof framing. (The treatment option in the amendment is boron, but other treatment chemicals may be considered in future.)
- People who do not want to use treated timber can use Douglas fir, but only for houses of defined low-risk design.
- Cantilevered deck joists and framing require a higher level of treatment, H3.2.
- The changes apply only to radiata pine and Douglas fir; there is no change for other species.
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What were the key issues raised in consultation?
The Department consulted on the changes in September and October last year and received 237 submissions. There was overall strong support for the proposals which are being introduced largely unchanged, but with some clarifications.
1. About 75% supported a single treatment class for framing timber. Three key points were raised in consultation:
Whether higher hazard classes should be allowed.
The Department encourages the use of H1.2, but acknowledges that designers may have particular reasons to use higher classes in certain situations. It is therefore continuing to allow higher treatments to be used (supported by sector education).
Whether roof trusses need to be treated.
In the interests of clarity, simplicity and inventory rationalisation, the Acceptable Solution specifies that roof trusses are to be treated to the same level as all other enclosed framing (apart from cantilevered deck joists and framing which require a higher treatment).
Whether all enclosed deck framing should be H3.2, rather than only cantilevered deck joists and framing as proposed.
The risk profile of other enclosed deck framing is not as high as that of cantilevered decks. Cantilevered decks depend more critically on the strength of the timber to prevent collapse. Therefore, only cantilevered deck joists and framing are specified as H3.2.
2. More than 90% agreed that H1.2 provides adequate protection from decay for enclosed framing. Two key points were raised in consultation:
Whether the H1.2 boron concentration should be higher.
The need for an increase in the concentration of boron (ie, the preservative involved) is not supported by the Department’s research or specialist advice.
Whether solvent-based azoles should be included as H1.2.
The proposal in the discussion document to exclude solvent-based preservatives from H1.2, was arrived at after considerable discussions with the sector, and submissions did not raise anything new. Therefore, solvent-based azoles have not been included as H1.2.
3. About 75% supported the use of untreated Douglas fir for houses of low-risk design. Three key points were raised in consultation:
Whether untreated Douglas fir is fit for purpose.
The science and expert opinion support the use of untreated Douglas fir for low-risk buildings. The Acceptable Solution therefore allows the use of untreated Douglas fir for houses of defined low-risk design.
Whether allowing untreated Douglas fir creates unnecessary complexity.
The Department sought to balance simplicity, risk and the provision of a chemical-free option for consumers. Douglas fir is therefore allowed for houses of defined low-risk design.
Whether wider use of untreated Douglas fir should be allowed.
Given the support for simplification, the risk to internal framing from internal wet areas, and the risk of transferred moisture from external walls, the Acceptable Solution does not provide for untreated roof framing or internal framing in other than low-risk houses.
The untreated Douglas fir option does not apply to commercial buildings, because some uses for commercial buildings may have a higher moisture risk.
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