Civil Engineering Reference
In-Depth Information
the side of the post or fix it on top of the post using some kind of bracket or strapping.
The specific details for your job should be included as detail drawings which will have
been established by your construction designer and/or engineer, and will form part of
your building permit. Obviously, you should refer to this information prior to cutting the
post. If you are finding it difficult to decipher the specifications do not guess; contact
your engineer or building consultant, as this is a crucial part of the structural integrity of
the building. If it is done incorrectly you will be forced to pull it down and redo it, even if
all the rafters are fitted above it.
The order of installation for a non-coupled roof
With a non-coupled roof the order of installation of the rafters is particularly important,
as it is the rafters that will hold the shape and position of the external walls and the ridge
beam. Start the process with the rafter at the centre of the ridge beam and work away
from that. Complete the installation of each individual rafter before moving on to
the next.
Measure the distance from the top outer corner of the external wall to the centre of
the top of the ridge beam. This will be the length of the rafters from the birdsmouth
notch to the plumb cut of the rafter. If the rafters are to be fitted side by side with the
rafter from the opposite side of the building, additional length will be added to the rafter
so that the bottom edge of the rafter will extend through to the top edge of its opposing
rafter (see Figure 8.15). In some instances it is necessary to cut a birdsmouth notch at the
top of the rafter where the rafter sits on the ridge beam.
Figure 8.15
Installation of a pair of rafters onto a load bearing ridge
Installing rafters for a non-coupled roof
The bottom rafter is to be skew nailed with one nail from each side of the rafter into the
timber at the external wall of the building. Now nail the rafter to the top of the ridge
beam with two skew nails. When the rafters from either side of the building are fixed side
by side to one another it is not normally necessary to cut a birdsmouth notch at the top
end of the rafters, however you will need to check the installation details that form part
of your building permit. As with floor joists and ceiling joists, the rafter from the
