Issue 29 – July 2011
When specifying and installing plasterboard ceilings, it is essential that the manufacturer's specific recommendations are followed to minimise the risk of cracking at sheet joints, particularly in large ceiling planes.
Where plasterboard is being fixed to timber framing (ceiling battens, ceiling joists, rafters, or truss chords), the timber must be dry – at a moisture content of not more than 18%, but some manufacturers require a maximum moisture content of 16% at time of fixing for a space that is not air-conditioned (8-18% for these spaces).
Other key fixing requirements for ceilings include:
- installing tapered edge sheet joints at right angles to the framing or ceiling battens
- using single length sheets to minimise the need for end joints
- incorporating relief joints into large ceiling areas.
For example, GIB require that tapered edge joints of their plasterboard sheets are made off framing using backblocking where:
- for timber framing with timber battens, there are three or more consecutive tapered edge joints
- for steel battens on timber or steel framing, there are six or more consecutive tapered edge joints
- a level 5 finish is required.