Amended B1 Compliance Document

In September 2006, the Department of Building and Housing published an amendment to its Compliance Document for Building Code Clause B1 Structure, which included referencing new amendments to New Zealand Standards that deal with timber grade properties and verification, and the use of timber for framing. The amendment to the B1 Compliance Document and material incorporated by reference was subject to a 6-month introductory period and became effective on 1 April 2007.

The amended B1 Compliance Document was discussed in Building Control Update 45 and in the September 2006 issue of Codewords. The amended B1 Compliance Document cites the following amendments to timber Standards.

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

Amendment 4 to NZS 3603 included several changes. It:

• introduced and provided the engineering properties for verified grades of timber, namely VSG and MSG grades
• down-rated the engineering properties of unverified, visually graded timber (No. 1 Framing)
• required that VSG and MSG timber be verified in accordance with NZS 3622:2004 Verification of Timber Properties.

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

Points to note

The amended B1 Compliance Document became effective on 1 April 2007. For timber designs to be in accordance with the B1 Compliance Document from this date:

• specific engineering designs must comply with Amendment 4 of NZS 3603
• non-specific designs, such as for housing, must comply with Amendment 2 of NZS 3604.

The amended B1 Compliance Document gives building consent applicants the choice of using No. 1 Framing or verified timber. Provided that designs are in accordance with the cited timber Standards, the use of all grades will result in compliance with the Building Code.

Many mills already produce verified timber and a number of others are working towards that goal. There is, however, no requirement for mills to produce verified timber as No. 1 Framing remains a recognised structural grade that is provided for in the timber Standards and the B1 Compliance Document.

Designers should not expect all grades of timber to be available in all areas. It is good design practice and simple common sense to check availability of grades before starting design work. If consented plans and specifications are based on a grade of timber that turns out to be unavailable, then the building will need to be redesigned and a variation to the building consent obtained before the work can proceed.

The Building Act 2004 requires that a code compliance certificate be issued if the work complies with the building consent, as stated in section 94(1). Accordingly, if you have already been granted a building consent, there is no requirement to change the design of the building to meet the amended B1 Compliance Document.

Further amendments to B1 Compliance Document

Note also that proposed changes to concrete, loading and masonry Standards are in development. See Building Standards Group Work in Progress opposite.