Design, not the timber, leads to leaky buildings, says expert

Poor design, not untreated timber, is the leading cause of leaky buildings, says a Canadian expert.

Dr John Straube told an Auckland University symposium yesterday that the biggest problem was modern designs which exposed building seams to wind and rain - simple things such as not having eaves or proper flashings on windows, flat roofs and enclosed decks.

Better design of wall systems would ensure that water which got in could also get out.

Dr Straube, who has a joint role with the University of Waterloo's civil engineering department and school of architecture in Ontario, said using untreated timber in a modern building in which moisture and rain were not controlled was like using a canary in a coalmine.

"You put some untreated timber in a building, so you found out [about leaks] sooner," he said.

Moisture problems in buildings had occurred in various countries with both wood and steel framing.

Untreated timber was also used in many countries. But the qualities of such timbers varied. Dr Straube thought the best of untreated New Zealand pinus radiata was equal to the worst of Canadian timbers.

But when the timber was treated to H1.2 [full sapwood penetration timber] it was better than the best of untreated Canadian timber.

But the essential thrust of Dr Straube's lecture was that buildings leak. Even a glass-clad building may eventually leak round the sealants.

He said there were buildings hundreds of years old which had been designed to cope with the present problems. "It's not new technology and its not rocket science."

Professor Geoff Duffy, of the Auckland University's faculty of engineering, said: "Wood is hygroscopic as well as bio-active, so we must keep water away from it or remove it when it does invade."

Greg O'Sullivan, of buildings surveyor Prendos, said comparing untreated pinus radiata with, say, douglas fir in Vancouver was not comparing like-products.

The douglas fir was much slower-growing and had a lot of natural turpentine, which increased its resistance to insects.

Mr O'Sullivan said the biggest problem New Zealand faced was to educate designers and builders.