Frame bottom plate overhanging the slab

So just before the bricks arrived, we pulled the fence down were the garage is zero lined on the boundary. Once the fence was down we noted that the frames were sitting out a little bit over the slab.

Didn’t look great, so we took a photo using a very scientific measuring instrument and sent them off to the SS.

SS rang my wife and told her he would fix it – I wasn’t on the phone to him but my understanding is that he said they would added some additional concrete under the frame.

We weren’t sure if that was sufficient so we had a look at the QBCC Standards and tolerances booklet which outlined the following:

4.11 Bottom plates that overhang concrete slabs
Bottom plates that are at least 90 mm wide and overhang concrete slabs by
in excess of 15 mm are defective and bottom plates that are 70 mm wide and overhang slabs by in excess of 10 mm are defective. In each instance, these permissible overhangs, are subject to the minimum edge distance for both the bottom plate and the concrete slab fixing locations being satisfied and minimum cavity widths as required by the Building Code of Australia also being maintained.

figure 4

Pretty clear that a 90mm stud frame is ‘defective’ if it overhangs the slab by more than 15mm.

So i went back and measured it with a tape measure:

Brendan Iphone 003

A 35mm over hang near the anchor bolt.

A bit more research and I discovered that the Anchor bolts should also be a minimum distance from the edge of the slab. Again the QBCC standards and tolerances guide has information on this

4.08 Fixing timber stud walls to concrete slabs
Fixing of timber bottom plates is defective if it does not comply with the Building Code of Australia, Australian Standard AS 1684 – Residential timber framed construction and the fixing manufacturer’s installation requirements. 
Depending on the manufacturer’s requirements for the concrete nail/masonry anchor used and the required uplift pull-out force and wind category, the distance of the fixing from the edge of the slab is required to be between 50 to 70 mm minimum for standard 20 MPa concrete.
The fixing point cannot be less than five times the diameter of the fastener
from the edge of the timber plate which equates to 25 mm for a 5 mm diameter nail and 50 mm for a 10 mm diameter masonry anchor.

The frames are 90mm, the over hang is 35mm leaving  55mm of frame over the slab. The centre of the anchor bolt is roughly 27mm from the inside edge of the stud frame meaning that it is approximately 28mm from the edge of the slab.

Doesn’t look good.

A further look at the slab found that the insertion of the anchor bolts had caused the slab to blow out!

Again, Not good.

So we have notified our CSC and our SS about this and have requested written evidence that the issue will be addressed by an an appropriately designed and certified engineered system so that it complies with this tolerance.

Our CSC has rang to organise a site inspection with the area manager and our SS for Tuesday 7am so we will see how it goes!








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