Civil Engineering Reference
In-Depth Information
Installation of the sub-floor bracing
Bracing
Beware of fitting the bearers and joists before fitting the stump bracing. You will have
details from either your consultant or engineer showing the requirements for bracing in
the sub-floor. If you need to fit bracing do not go on with any other work until all the
bracing is fitted. Stumps can easily be bumped out of position. Bearers and floor joists
fitted to incorrectly positioned stumps will more than likely be too long, or even worse,
too short. Either way, you will have to disconnect the stumps and reposition them. It may
be that all the bearers and joists have to be removed. It is not uncommon to damage
timber when removing it, which will increase the cost of the job. Do everything in its
right order and things will flow much more smoothly. The building regulations require
that sub-floor bracing material is to be not less than 150 mm above the ground. This
detail should be on your specifications, but if not, you will need to contact your
consultant or engineer.
Sub-floor bracing of timber stumps
With timber stumps it is a simple process. Measure the brace length once the stumps are
in position. Ensure that the stumps are vertical, and check on the string line, which
should still be on the hurdles, that the stump is in the correct position relative to the
external wall requirements: then nail the brace to the stumps. When nailing do not be
over zealous as you are going to have to drill a hole through the brace and stump to fit a
bolt. Once all the braces are in position, again check that the stumps are vertical and in
particular check the external stumps. If the external stumps are out of alignment your
floor is going to be wrong. The floor will set the position of the wall, which will cause the
roof to be out of shape. The quickest way to detect misaligned stumps is to look along the
plinth boards fitted to the stumps. I wish I could say that this has never been a problem
for me, but I must admit I have on more than one occasion had to remove braces and
adjust the position of the stumps.
Bolting sub-floor bracing to the stumps
Timber stumps
The junctions of all the braces to stumps are to be bolted. A 10 mm bolt is the most
common size used, however check your engineers' details. You could use a coach bolt or a
hex head bolt. I would recommend that you use hex head bolts, as it is much easier to do
these up tight. A coach bolt has a dome head with a square protrusion below the head.
This protrusion is designed to lock into the timber so that the head will not spin when
the bolt is tightened. If these bolts are not put in cleanly this protrusion will have little
affect and it will be almost impossible to tighten the bolt adequately.
Concrete stumps
Not only would it be difficult to drill holes in concrete stumps, but it is not permitted.
A 'U' bolt specifically made to suit the concrete stump is used to fix a brace to a concrete
stump. Hold the brace in position next to the stump and mark the brace with the
required location of the holes into which the U-bolt will be inserted. Once the two holes
