Changes have been made to the New Zealand timber treatment specifications in response to frequent incidences of decay in framing timber and doubts about the long-term performance of tributyltin formulations when used in exposed situations. Changes have been made to Hazard Class H1 to allow a level of treatment to provide short to medium decay resistance to framing which would protect it, should leaks in the building envelope develop, until such time as those leaks are detected and rectified. Changes have also been made to Hazard Class H3, so that use of tributyltin light organic solvent preservatives is restricted to those products whose structural integrity is not critical to a buildings long-term performance. These changes have been included in a 2003 revision of the NZ Timber Preservation Council Specifications which are now published as NZS 3640:2003 "Chemical preservation of round and sawn timber". They have been undertaken in conjunction with changes to other Standards and Codes which affect the use of timber in NZ building construction.

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