The use of weaker framing timber is adding to the building industry's leaky home headaches.
Felling of younger radiata pine in recent years has meant the timber lacks the long fibres that give stiffness and strength, says Branz, the Building Research Association.
As a result, changes are being considered
to the timber design standard, says Branz structural engineer Roger Shelton.
In the latest issue of the association's Build magazine, Mr Shelton said there was a proposal to modify the strength and stiffness values of visually graded, but not machine stress-graded, framing timber.
Such a change could potentially affect the timber framing standard as well and "will have a significant impact on the whole building industry", he said.
About half the timber used to frame New Zealand homes is visually graded. Other countries such as Australia require machine stress-grading for nearly all home building.
The proposed change to the timber design standard has been delayed for about a year because of disagreement among experts.
The Building Industry Authority's structural (civil) adviser, Dennis Monastra, said timber was the only material that had its properties tested by sight.
In Build, Mr Shelton said inadequate strength could cause cracking or fracture of framing members and loosening of joints or fastening systems.
- NZPA
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Feature: Leaky buildings
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