Civil Engineering Reference
In-Depth Information
Chapter 3, on timber floor construction. Fix the ceiling joist at the outer wall of the house
first, ensuring that the ceiling joist is level with the outside of the timber it is being fitted
to. This will mean that the ceiling joist may protrude past the internal wall by as much as
150 mm. Do this along one outside wall only, and then fix the other end of the ceiling
joists at the internal wall. The ceiling joists can now be fitted to the opposite external wall
in the same manner. When completed you will find that the internal end of the ceiling
joist is against a ceiling joist that has already been fixed to the top of the internal wall.
This will mean that it is not possible to fix the new ceiling joist with two skew nails, as the
existing ceiling joist is in the way. In this instance, first fix the joist to the top plate with a
skew nail, and then nail the new ceiling joist to the existing one using a 75 mm nail
horizontally from the new joist to the original approximately 20 mm down from the top
of the new joist.
Installation of hanging beams
The section drawing of the approved plans will show whether hanging beams are
required, as will the timber specification schedule. Refer to the schedule for details on
dimension and timber requirements. The hanging beam is positioned on top of and
across the ceiling joists. Hanging beams are required when the width of the ceiling is
greater than the capacity of the timber to carry the weight of the ceiling. When the
hanging beam is fitted across a room from one internal wall to another, the hanging
beam will be cut square at each end. When the hanging beam is fixed to an external wall
from which the roof is pitched, it will have to be cut at an angle, otherwise the hanging
beam will protrude above the roof line.
The traditional method of fitting hanging beams
The traditional method of fixing a hanging beam is to lay it across the ceiling joists in its
vertical position. Using a sash clamp, hold the ceiling joists and hanging beam together
and then skew nail the beam to the ceiling joist with a 75 mm nail through both sides of
the hanger into the ceiling joist. You are required to fix the ceiling joists to the hanging
beam using either metal joist straps or timber droppers. A metal joist strap or timber
dropper is fixed to the side of the hanging beam in line with the junction of the ceiling
joist to enable its fixing into the side of the ceiling joist (see Figure 7.2). The timber
droppers could be made of 35 × 35 pine, however the metal joists straps are cheaper and
easier to fit.
Figure 7.2
Plan view of joist straps at the junction of the hanger and ceiling joists
