Rot set to lift cost of new home

By ANDREW LAXON

The price of new homes is set to increase if the building industry heads back to chemically treated timber as a last defence against leaks and rot.

Six years ago, New Zealand controversially dropped the compulsory use of treated timber in wall frames as unnecessary, despite protests from some experts.

But evidence has gradually emerged of a leaky-house crisis, which some believe will cost at least $1 billion in repair bills.

Industry insiders believe thousands of homes built in the past decade have leak and rot problems, with one in 10 new homes potentially at risk

Three months ago, an independent inquiry for the Building Industry Authority urged immediate action.

The question of treated versus untreated timber is hotly debated. Many builders and repair specialists believe lack of chemical treatment to protect timber wall frames from rot is at least partly to blame.

Timber sellers reply that the problem is poor design and workmanship - no amount of treatment will save wood once it gets wet.

However, Weekend Herald inquiries have revealed an industry backdown which would effectively force builders to start using treated timber again on many of the new houses most at risk from leaks - Mediterranean-style homes with walls made of one-piece materials such as stucco, fibre cement or polystyrene.

Estimates of the extra cost range from $1000 to $4000 a house.

Under draft rules prepared by the authority, these homes would require H3-treated timber - the standard now required for exposed outside areas such as decks - for timber wall frames if there was no gap between the outside cladding and the frame allowing water to drain away.

All new houses would need H3-treated timber on the bottom plates of wall frames, a change the authority says is crucial.

If the changes are agreed on, builders will either have to follow them or present their own equally waterproof solutions to a building inspector or certifier.

The authority's chief executive, Bill Porteous, said the proposals had been put forward by a working group last year when the authority began hearing about leaks.

But he admitted that extensive publicity this year - led by an investigation in the Weekend Herald - had forced the authority to move faster and find a short-term answer.

"Indications are - and we're testing public mood on this - that something fairly urgent needs to happen."

He hoped a more conclusive long-term solution would come in the next few months from tests by the Forest Research Institute comparing treated and untreated timber.

The inquiry team's final report is due at the end of next month.

The Building Research Association of NZ's weathertightness manager, Adrian Bennett, conceded that the about-turn on treated timber might be cold comfort for owners of houses built since 1996.

"The issue is we should have been building weathertight buildings through the entire period. It is unfortunate. It will make perhaps some homeowners feel that they don't have as much robustness in their home as someone who gets one next year, if this goes through."

Mr Bennett, who also chairs the building industry's weathertightness group, said any return to widespread use of H3 timber would probably raise environmental concerns for some people.

The treatment - previously made up of copper, chrome and arsenic - now involved a heavy-duty chemical called tributyl tinoxide. Sawdust and offcuts had to be disposed of carefully.

He estimated that the change could add $2000 to $4000 to the cost of an average home. It would affect about half the 20,000 new homes built each year.

However, Chris Preston, chief executive of the Master Builders Federation, put the average cost at $1000 to $1200 extra on a typical $250,000 house.

He said his members supported the change as a prudent measure, although he felt that reports of the number of leaky houses were exaggerated.

Building Industry Federation chairman and Carters chief executive Richard Carver said he supported anything that would make New Zealand buildings more weathertight.

But he added that H3 timber would still not protect wood against water for long, as timber sellers had always said.

The only real protection would be H6 timber - the marine ply used for boats.

Mr Carver estimated that the changes would cost $1000 to $1500 for an average home and up to $3000 for an expensive one.

The draft proposals are available for public comment on the authority's website until August 23. The authority will then consider the submissions and write the final regulations.

The changes would not affect timber used in unexposed parts of a house, such as internal walls and ceilings.