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BC Update: No.45 - Department references amendments to timber Standards in the Compliance Document for Clause B1 (Structure)

14 September 2006: The Department of Building and Housing has amended the Compliance Document for Building Code Clause B1 (Structure) by referencing two amendments to New Zealand Standards that deal with timber grade verification and the use of timber for framing.  This is Amendment 7 to the B1 Compliance Document.

The amendments to the Standards being cited are:

  • Amendment 4 to NZS 3603:1993 ‘Timber Structures Standard’
  • Amendment 2 to NZS 3604:1999 ‘Timber Framed Buildings’

Amendment 4 to NZS 3603:

  • introduces, and provides the engineering properties for new verified grades of timber, namely VSG and MSG grades
  • down-rates the engineering properties of unverified, visually graded timber (No. 1 Framing).
  • requires that VSG and MSG timber be verified in accordance with the provisions of NZS 3622:2004 ‘Verification of timber properties’.

Amendment 2 to NZS 3604 is a direct consequence of Amendment 4 to NZS 3603.  It amends the tables and design information in NZS 3604 to account for the new VSG and MSG grades and the revised properties of No.1 Framing.

Points to note:

  • The amended Compliance Document will not become effective until 1 April 2007. This will allow further time for timber millers to implement the necessary systems should they wish to produce verified timber.  The introductory period will also allow further time for the industry to familiarise itself with the new provisions.  During the introductory period, building consent applicants can choose to use the amended Standards as an Alternative Solution proposal.
  • No. 1 Framing remains approved for structural use.
  • The amended Compliance Document makes it clear that the initial grading for MSG timber is based on joint Standard AS/NZS 1748:1997 and not on the 2006 version of the joint Standard released in February.  The differences between the two versions of the Standard are considerable and the 1997 version of the Standard will be retained pending a full review.
  • The Department is aware of concerns that NZS 3622 does not sufficiently detail the verification auditing procedures for timber grading.  The Department will work with industry to get agreement on the necessary auditing procedures during the six-month introductory period.

The amended B1 Compliance Document is available on the Department’s website.