Untreated timber will soon be banned as a building material in outside wall frames as a result of the leaky homes crisis.

The Building Industry Authority yesterday announced that it would release proposed changes to the Building Code for consultation next month.

Chairman Barry Brown said the new rules would clearly signal a change to the present regime, including "a move away from the use of untreated timber in risky situations like external wall framing".


The Herald understands the authority will recommend a return to boric-treated timber, which has not been compulsory since 1996.

The standard is likely to be a new treatment, known as "H1 Plus", which gives medium-term protection against rot but is less toxic than the H3 standard required for outdoor timber such as decks.

The authority was about to make H3-treated timber compulsory from December 1 last year but pulled back because of industry, political and environmental concerns.

The rethink is expected to lead to the introduction of H1 Plus, which the Forest Research Institute estimates will protect timber from rotting for at least five years - long enough for most leaky home owners to discover the problem and make repairs.

The change could add about $3000 to the cost of a new home, if treated timber framing is used throughout the building.

At this stage the new standard is expected to apply only to parts of the building which are exposed to water. But some industry experts claim this will be too confusing and predict it will soon cover timber framing throughout the house.

The 1996 change to "chemical free" timber is regarded as a leading cause of the leaky building crisis, as untreated timber rots much faster when it gets wet.

In 1999 forestry scientist Dr John Kinnonmonth, the chairman of the committee that changed the rules, was so appalled by the results that he wrote to the authority urging it to reconsider the decision.


His plea was ignored.

The change was driven by timber giant Carter Holt Harvey, which wanted to replace chemically treated timber with the cheaper kiln-dried wood it was already exporting to Australia.

Forestry scientists were furious at industry advertising by Carter Holt and its rival Fletcher Forests, which pushed the changeover by claiming that boron treatment gave no more protection against rot than their untreated timber. Carter Holt was later found guilty of misrepresenting its LaserFrame product by the Advertising Standards Complaints Board.

Mr Brown said next month's review would also include recommendations over the continued use of copper, chrome and arsenic (CCA) treatment, which was being reviewed separately by the Environmental Risk Management Authority for health and safety reasons.

Last week Commerce Minister Lianne Dalziel announced the Government's proposals to combat the leaky home crisis by registering all building professionals, protecting home buyers with compulsory insurance and rewriting the Building Code.

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