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BC Update: No.44 - Standards New Zealand publishes changes to NZS 3640

21 August 2006: Standards New Zealand today published an amendment to NZS 3640 (Chemical Preservation of Round and Sawn Timber)

The amendment Number 3 to NZS 3640 includes, in part, that timber treated with Boron to H3.1 shall have:

  • 0.8% BAE (Boric acid equivalent) with full sapwood penetration
  • pigmented coating applied to all timber surfaces, after treatment and before despatch from the treatment plant
  • other timber branding requirements.

The Department is not able, at this point, to determine whether the amendment as drafted would be compliant with the performance requirements of the Building Code.

The Department of Building and Housing supports the intent of the amendment to allow greater use of boric treatments. The Department believes they are a big step forward in the timber treatment process. However, the Department is concerned that the amendment as published by Standards New Zealand is not clear about what uses timber treated with Boron to H3.1 may be put to.

The Department is concerned that the Standards Committee which has created the amendment has focused solely on the ability of the timber treated in this way to withstand rot and has not considered issues such as:

  • the treatment’s fitness-for-purpose where it might be used as structural framing.
  • the effect of the treatment’s paint protection on adhesives and synthetic underlays
  • the potential for the treatment’s paint protection to disguise stress grading and other timber markings.

These are critical issues in terms of meeting the requirements of the Building Code.

The Department will now assess the implications of the amendment to the Standard in terms of the performance requirements of the Building Code.

In the interim, the Department of Building and Housing advises that the amendment should be treated as an alternative solution in terms of the Building Code.

The Department will advise further at the completion of its investigations.

Any comments or requests for information should be directed to Standards New Zealand.