Industry tries to calm timber-rot fears

Dr Mick Hedley with untreated timber (left) and timber treated using the "spray on" treatment. Picture / Amos Chapple

Building agencies moved swiftly yesterday to allay fears of a second wave of rotting houses as claim and counter-claim flew around the reliability of kiln dried framing timber treated with a surface spray.

The Auckland City Council says it will reject building consent applications specifying the T1.2 coded timber, coated with TimberSaver preservative, until the Department of Building and Housing indicates where the product can be used.

Its building inspectors will require treatment certificates and, if necessary, testing to ensure the timber has been adequately treated.

TimberSaver manufacturer Osmose NZ says it is the victim of pre-election politics and the council's response is overkill.

"This is rubbing salt into homeowners' wounds after leaky buildings," said Osmose technical sales manager Terry Smith. "It is nothing more than political point scoring ...

"We are happy to go through the review process - there are no skeletons in the closet."

But the council's principal building officer, Bob de Leur, said it already faced 1100 leaky building claims and had to be cautious.

"We have to make sure we don't lumber the ratepayers of Auckland with future problems," said Mr de Leur.

The Department of Building and Housing sent advisories to about 2000 industry participants, reminding them to follow product usage guidelines for all products, including timber framing. Large suppliers were reminded to market products according to conditions on their use.

Scientists remain split over the durability of T1.2 timber after long-term exposure to rain. It is spray coated with a boron-based preservative whereas conventional H1.2 timber is soaked in boron for cross-penetration to a 0.4 per cent content level throughout.

Building experts said the row showed how far the industry had to go to address concerns about product appraisal and accreditation, and communication on conditions of use.

The new timber gained Building Industry Authority approval last year for use in the same situations as H1.2 timber provided it is kept dry and any cut edges are sealed.

But building surveyor Greg O'Sullivan and Certified Builders Association chief executive Gary Shuttleworth say it is being sold as H1.2 grade and could be misused.

Mr O'Sullivan, of Prendos, said widespread failure of T1.2 treated timber was unlikely because of its boron content.

"The concern we have is that it is being sold when H1.2 was ordered. We believe this is misrepresentation of the product and its conditions of use."

Institute of Building Surveyors chairman Kevin Longman said giving surface-treated timber the same status as fully penetrated wood was "obvious nonsense".

Experience with building failures showed that continual water penetration caused boron to leach out even when treatment involved full cross-penetration, said Mr Longman.

The industry had toughened standards for treatment and durability after the leaky homes scandal. "To then provide accreditation for an alternative which is less than [the treatment standard] is in my opinion another backward step," he said.

Osmose's Mr Smith said tests found T1.2 wood could withstand at least two months' exposure to rain before significant loss of boron content.

When wet, boron tended to spread further into the timber rather than to leach out. The amount of leaching was similar to that in conventionally treated timber.

Forest Research Institute scientist Dr Mick Hedley said T1.2-treated wood worked if installed according to conditions of use.

"But there are some restrictions on how it should be used and these are not explained to builders."

Laboratory tests showed it remained resistant to fungal decay, said Dr Hedley, an expert on wood preservation.

But wood scientist Robin Wakeling stood by his claim that the product was not sufficiently proved. "It's totally unorthodox to approve something after 1 1/2 years of testing."

The wood is marketed as Origin Timeframe by Carter Holt Harvey Wood Products.

* The Department of Building and Housing is reviewing the approval process for TimberSaver-treated wood and the use of the product to see if there are any grounds for concern.

* At least one local body, the Auckland City Council, will not accept building consent applications specifying the timber until the department indicates where it can be used.

* Building Issues Minister Chris Carter says the investigation will be speedy and the public notified as soon as possible.