Weathertightness failures in New Zealand buildings due to the combined effects of cladding choices, design and construction faults and the use of untreated framing timber has led to the so called ‘leaky building syndrome’. The latest estimated cost of the leaky building crisis in New Zealand is about NZ$11 billion. This research was conducted to provide a better understanding of the options of using in-situ preservative treatments for controlling incipient and early decay in framing timber which is still structurally sound when remediating leaky buildings. The research approach involved taking untreated radiata pine sapwood, pre-infecting it with common brown rot fungi either Oligoporus placenta or Gloeophyllum sepiarium, applying a brush-on timber treatment of either boron-glycol or copper naphthenate to one or more sides, and then maintaining the samples at elevated moisture conditions. After specific durations, the samples were examined and tested to determine the effectiveness of the treatments in slowing down or preventing decay from progressing using measurement of stiffness (express as modulus of elasticity) and decay (expressed as an index of condition). Assessment confirmed that the performances of both preservatives improved as more sides of timber were treated. However, there were significant differences in efficacy of both preservatives. Boron applied to three or four side appears to have been effective in preventing decay from progressing. Copper naphthenate at the concentration used has not been successful in preventing decay, regardless of the number of faces treated. The treatment retention in samples treated with boron on three or four sides was about 0.4% (BAE w/w) and 0.65% (BAE w/w) respectively. This is close to or above the cross-sectional retention required by New Zealand H1.2 (interior framing) specification.

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