Timber House Piles
26 January 2012
We have heard that incorrectly specified timber is being used as house piles.
Only piles that are produced in compliance with the standard NZS3605:Timber piles and poles for use in building will satisfy the requirements of the New Zealand Building Code.
NZS3605 specifies physical properties, grade and preservative treatment requirements for timber piles. In addition, timber house piles must be branded with a recognised triangular mark which contains identifying numbers for the treatment plant, the preservative used and the hazard class. Anchor piles are marked with an "A" as well as the triangular brand.
1 Physical properties:
- The standard cross section dimension for sawn house piles is 125mm x 125mm but they may be larger.
- The minimum diameter for a round house pile is 140mm except that they may be as small as 120mm diameter within 200mm of either end or may be pointed to facilitate driving into the ground.
- The maximum length of a house pile is 3.6m.
- Round piles have a straightness requirement and sawn house piles have limitations on permitted warp.
2 Grade:
- Timber house piles must be graded to No1 Framing as per NZS3631:1988 New Zealand Timber Grading Rules.
- Sawn anchor piles must have their physical properties verified by proof testing conducted in accordance with procedures set out in Appendices A and B of NZS3605. In simple terms the tests involve the application of a load of 3.3 to 4.1 tonnes to the face of a pile for a period of at least 10 seconds without the piece showing signs of distress or permanent damage.
- Sawn house piles of Pinus species that are 3.0m or longer must have no less than four growth rings between the pith and the nearest sawn face.
3 Treatment:
- All timber house piles must be treated to a minimum H5 hazard class
To summarise, wooden house piles of sawn or round timber are manufactured to a standard that requires certain physical properties, grades and treatment levels to be met. These piles are made by licensed producers and they are identified by a specific brand which appears as a permanent mark on the pile.
A list of Woodmark registered house pile producers is set out elsewhere on this website.