Civil Engineering Reference
In-Depth Information
that is, the top of the plumb cut, to line 'B1' where it intersects the top edge of the roofing
boat. Cut a piece of timber, ideally flooring, 40-60 mm wide and 20 mm deep equal to
the space between the plumb cut and the top of 'B1'. Fix this piece of timber to the top of
the roofing boat with the end level with line 'B1' where it intersects the top of the roofing
boat, allowing it to overhanging each side of the boat by equal amounts (see Figure 8.13).
Further details on how to use the roofing boat are on page 148.
The support of rafters for a stick framed roof
Either your building consultant or engineer will have determined the timber
requirements for your roof and they will be detailed in the timber specification schedule
of your building permit. Ideally you will also have a detailed drawing of the positions that
the rafters are to be fixed, and details of the angle cuts of the rafters.
Stick framed roofs will either have the rafters supported at each end of the rafter, or
the rafter will be supported at the outside wall and be fixed to the side of a piece of
timber at the peak of the roof called the
ridge beam. Rafters supported at each
end will rest on either a wall or a beam.
More often than not, the rafter will be
supported at the outside of the building
by the external wall, however, when the
building incorporates a verandah the
rafter will be supported on a verandah
beam supported by verandah posts (see
Figure 8.14).
For a straw bale house the rafters will
either be fitted to the ring beam fixed to
the posts around the perimeter of the
house, or to the top bale boxing after it
has been leveled. Using a carpenter's
pencil, mark the positions of the rafters
on the top of the external walls as
detailed on the roof layout drawing. If
the house has a ceiling separate to the
rafters, these positions will have already been established prior to the installation of the
ceiling joists. In this case the rafters are to be fixed beside the ceiling joists.
Figure 8.14
Installation of rafters for the main roof and the
verandah, coupling them together at the top boxing
Non-coupled roof
When a load bearing ridge beam is to support the rafters it will obviously be necessary to
first fit the ridge beam. The size of the beam will be detailed in the timber specification
schedule of your building permit. This beam may be supported on posts or be seated on
walls. In most instances the beam will be supported on posts.
Once all the supporting posts are securely fixed in place the beam can be fitted to the
top of the posts. It may be necessary to cut the beam into the side of the post, bolt it to
