Issue 19 – August 2010
When specifying proprietary bottom plate fixings to slab on ground construction:
- What is the rating of the fixing proposed? Does it have the required rating for (a) the bottom plates (see NZS 3604:1999 clause 7.5.12) or (b) the proposed proprietary bracing system.
- What depth of concrete does the fastener require?
- Can the edge distance requirement for the fastener be achieved?
- Does it meet the durability requirement? In concrete, 50 mm cover is required in all zones. Permanent concrete masonry formwork requires cover of 60 mm in the sea spray zone, which may not be achievable with 90 mm framing. Both concrete and masonry foundations require a minimum of 25 MPa concrete in the sea spray zone. Lesser cover may be allowable in other zones but these lesser covers could be overridden by the structural edge distance requirements for proprietary fasteners.
When installing screw anchors, make sure the drill bit used is in good condition and will drill the correct diameter hole. Worn drill bits will cause the fastener to bind in the hole.
Reproduced from BRANZ Guideline, July 2010.
Related Touchstone article