Once the plumbing and wiring have been roughed in, it’s time to put in insulation and internal linings (normally plasterboard) on the internal walls and ceilings of your home. This can all happen either before the lockup stage (i.e. when your home can effectively be 'locked up') or afterwards, depending on what’s been agreed upon in your contract.
How is wall insulation installed?
The way insulation’s installed will depend on what’s been planned or designed for your home. The walls in the vast majority of Australian houses are insulated using glasswool or rockwool insulation batts, which are designed to sit in the cavities between the wall studs.
Insulation batt sizes
The size of the batts required will depend on:
- The thickness or depth of the timber frame elements – this determines the thickness of the wall. Timber frames are normally either:
- 90mm or
The thicker the framing elements, the thicker the insulation batts that can be used (and therefore the higher the R-value that can be achieved).
- The distance between the wall studs – This is normally either 450mm or 600mm.
- Whether it’s a timber or steel frame – Steel frames are narrow and have channels in them, allowing for slightly wider insulation batts than can be used with.
Below is a basic table demonstrating what sized batts would normally be used with different spans between wall studs:
|Batt width for timber frame||430mm||580mm|
|Batt width for steel frame||450mm||600mm|
To ensure that wall insulation is effective, it’s very important that insulation batts are installed absolutely correctly. Small gaps or parts where insulation batts are ‘stuffed’ or compressed too tightly into places they don’t quite fit will reduce the overall effectiveness of your wall insulation and allow heat to leak in or out.
How is plasterboard put up on walls?
Nearly all homes in Australia use plasterboard as a lining for interior walls. It’s lightweight, easy to work with, looks good, is easily painted – and some types do a very good job of preventing sound transfer too. Plasterboard is supplied in sheets, which are normally either 1200mm or 1350mm high. The height you’ll need will usually depend on how tall your ceiling will be. These sheets are first carefully cut to size, then they’re adhered to the wall using a ‘stud adhesive’. Once they’re in place they are either nailed or screwed to the wall studs. Joins between the boards are filled with a plaster-based cement base coat and covered over with a piece of paper tape to cover the joint. Once dry, this is sanded smooth and covered over again with a plaster-based cement topping coat which is also sanded smooth once it dries to create a nice seamless finish.
How are corners plastered?
Internal corners where walls meet (e.g. the corner of a room) are finished with the same method using a folded piece of paper tape. External corners, on the other hand, are finished with an ‘external corner bead’, which is typically an L-shaped bit of aluminium that’s used to create the corner. Once in place, this is carefully plastered over to create a nice straight corner.
How is plasterboard put on ceilings?
Obviously it’s pretty important that when plasterboard is attached to the ceiling joists, it’s attached so that it stays there. It’s also important that when the plasterboard is fixed, and good to ensure that it’s nice and straight. While plasterboard can still be fixed directly to the ceiling joists, these days that’s a lot less common. In most new houses, either 'ceiling battens' or 'furring channels' are attached to the undersides of the ceiling joists to make it easier to attach the plasterboard.
What’s the difference between ceiling battens and furring channels?
A bit of trivia: one of the questions that often gets asked (and rarely gets answered) is what the difference is between these two things. In a nutshell, a steel furring channel is much stronger, and is what’s normally used in commercial construction. Furring channels are sometimes called ‘hat channels’ because if you look at them from the ends, they’re the shape of a top hat. As well as ceilings, furring channels can also be used to attach plasterboard to walls. Ceiling battens, on the other hand, are normally only used for ceilings, and only in residential construction. Ceiling battens can be made of either steel or timber – but steel’s normally preferred because it’s straighter. In most cases, your plasterer should use the systems and methods that are recommended by the plasterboard manufacturer. The furring channels or ceiling battens are attached to the underside of the ceiling joists (using fixing clips in the case of furring channels), so that they run at right angles to the joists. The spacing between them will depend on the type of plasterboard being used. Once the battens or furring channels are up, the plasterboard is hoisted using a special ‘sheet lift’ (or by hand using scaffolding) and screwed or nailed directly into the channels at set spaces so that the fixings are flush with the surface of the plasterboard. When that’s done, the edges are finished with paper tape and plaster cement base and topping coats as they were for the corners of the walls.
How cornices are installed
If cornices are going up, these need to be carefully cut to size and cut at the correct angle using what’s known as a mitre - which is a tool to guide a saw through an exact angle. The pieces of cornice are then ‘buttered’ using a small layer of plaster cement, and carefully fixed into place (sometimes with nails to hold them in place). Joins between lengths of cornice are then carefully finished at the joins with plaster cement for a sharp, clean edge.