Civil Engineering Reference
In-Depth Information
be that your engineer requires that the
collar ties be bolted to the rafters, as is the
case with barn style roofs.
If you have an assistant, have them
hold one end of the collar tie in position
while you nail your end to the side of the
rafter, and then have your assistant nail
their end to the rafter. If you are working
alone, hammer a 75 mm nail into the side
of the rafter leaving the nail protruding
from the timber as a support for the collar
tie. Do this to all the rafters down one side
of the construction. To fix the collar ties,
simply rest the other end of the collar tie
on the nail protruding from the rafter and
fix your end of the collar tie. You can work
your way along the building fixing one end
of each collar ties and then nail the other
end of each collar tie.
Collar ties/ceiling joists for barn style
ceilings
When you require a barn style shape to
your ceiling, the collar ties will double as a
ceiling joist, so that the ceiling lining is
fitted to the underside of the rafters for the
first section of the ceiling and then to the
underside of the collar tie (see Figure 8.33).
When installing the collar ties for this application it is important that all the collar ties/
ceiling joists be in line with one another. The simplest method to achieve this is to fix a
string line to the underside of the rafters in a position that represents the underside of the
collar tie/ceiling joist. The collar ties will then be fitted relative to the string line. When
using a string line as a guide for the installation of timber, always fit the timber slightly
away from the string line. If the timber is resting against the string line it is difficult to
judge whether the timber is in the correct position or whether it is actually pushing
against the line which would, in turn, give incorrect guidance for the installation of the
next collar tie.
Collar ties that also take the form of the ceiling joists contribute a more than
significant part of the structural integrity of the roof, as they alone prevent the roof from
dropping and prevent the external walls from being pushed out. There should be specific
details in your building permit dealing with the installation of this timber. If you are
unable to locate it or unclear as to the instructions do not proceed until the information
is clarified either by your building consultant or engineer. It is normal for the collar ties/
ceiling joists to be both nailed and bolted to the rafters. When they are to be bolted, it is
Figure 8.33
Installation of a collar tie to the sides of a
pair of rafters in a coupled roof
