BC Update: No.71 Review of Timber Standards | Boron treated solid timber cladding

17 September 2007: In August 2006, Building Controls update No. 44 was issued, announcing the Department’s concern over Amendment 3 to NZS 3640 complying with the Building Code.  The Department’s concerns related primarily to points (1) and (2) below.

Amendment 3 to NZS 3640 includes:

1. Boron treated timber cladding to H3.1, incorporating a pigmented paint coating applied at the treatment plant
2. Boron treated timber framing to H3.1, incorporating a pigmented paint coating applied at the treatment plant
3. A reduction in concentration of copper naphthenate in H 3.1 treated timber claddings less than 30 mm thick, and with continuous face branding.

As a result of further work with industry to clarify point (1) above, the Department is now satisfied the amendment relating to points (1) and (3) complies with the Building Code.

Support by the Department for that part of NZS 3640 Amendment 3 relating to H3.1 treated solid timber used for cladding such as weatherboard ,facings and joinery, is valid if:

• the minimum treatment concentrations are as outlined in NZS 3640:2003 Amendment 3
• the Boron-treated timber is coated with a grey pigmented oil alkyd or modified acrylic or modified latex, applied by brush, roller, spray, or vacuum process before despatch from the treatment plant
• the properties of the pigmented coating comply with either AS 3730 Part 13 (solvent-borne) or Part 17 (latex), as appropriate
• each piece of timber, at point of sale, carries a clear, legible, adhered notice stating that:
  • all cut surfaces, especially cut end grain and bore holes greater than 25mm, have a coat of priming paint, brush or roller applied before fixing in place (the priming paint is to be well worked into the cut timber, especially cut end grain)
  • all factory pre-primed end grain surfaces have an over coat of brush or roller applied priming well worked into the end grain before fixing in place.

NOTE: Work between the Department and industry on the part of Amendment 3 relating to point (2) above (Boron treated timber framing to H3.1) is not yet concluded and therefore Building Controls update No. 44 on timber framing remains in force.