Civil Engineering Reference
In-Depth Information
to be installed first. This timber is to be
cut with the long point closest to the
ceiling so that when the joining timber
is fitted it can simply rest on top of the
first piece of ridge material (see Figure
8.26). The joint will eventually have a
nail plate fitted to each side of the ridge
to prevent the ridge timbers from
parting.
If your roof is a hip roof, you will
need to cut one end of the ridge square,
and then mark the ridge from that
point to the other end with positions
that correspond to the marks on the
external wall for the location of the rafters. This will enable you to easily fit rafters in the
correct position with the rafters at right angles from the ridge and external wall.
The first rafters to be fixed will be the rafters at each end of the ridge, which are the
jack rafters. While as a tradesman I am able to perform the next process alone, I would
suggest that you get assistance unless you have significant experience and the roof is not
out of your normal reach.
When it comes time to fit the rafters it will make it a lot easier if a nail has already
been partly hammered into the top edge of the rafter so that it can simply be hammered
in further to fix the rafter to the ridge. Hammer a 75 mm bullet head nail into the top
edge of the rafter toward the plumb cut until the point of the nail is about to break
through the face of the plumb cut. Once the rafter is in position against the ridge, this
nail will be hammered into the ridge as the initial fixing of the rafter to the ridge.
Figure 8.26
Joining of a ridge beam with 45-degree angle
cuts and nail plates
Assembling the rafters and ridge beam
Positioning the ridge on top of the ceiling joists
Lay the ridge beam on top of the ceiling joists approximately in line with the position
that it will eventually be fitted. The first rafters to be fitted shall be jack rafters 2 and 3.
Have your assistant position themselves so that they can support the top end of the rafter
roughly at the correct height. With your assistant supporting the top of the rafter at near
to the correct height, fix the bottom end of the rafter to the external wall or beam. Ensure
that the birdsmouth checkout is tight against the timber of the external wall and that the
rafter is against the ceiling joist, if applicable. Using 75 mm nails, skew nail the rafter at
the birdsmouth into the top of the wall, and make a second fixing horizontally into the
ceiling joist. Repeat this process for the rafter on the opposite external wall. The person
holding the top of the rafters should not place the top of the rafters together at this point,
as this will cause the second rafter to slip away from the outside wall. Once the bottom of
the second rafter has been securely fixed to the external wall as previously detailed, the
two plumb cuts at the top of the two rafters can be sat together. At this point your
assistant will no longer be carrying any weight, but merely steadying them in their
upright positions.
