Thermal insulation for the most common forms of external wall types should be installed during construction, as existing walls can be difficult and costly to insulate. In these cases, the insulation is installed between the inner and outer layers of the wall cladding. Walls of solid masonry - such as stone, mud brick and rammed earth brick - can only be insulated on either the inside or outside surfaces.

Depending on the climate, a suitable level of insulation should be installed, as recommended in Australian Standard AS 2627.1 - 1993.

Brick Veneer, or Lightweight Timber/Steel Frame covered with Weatherboard

These walls can be insulated using a variety of products, such as reflective foil laminates (RFL), or insulation batts, sheets or boards. In most circumstances, a bulk insulation is recommended. Reflective foil laminates can be used, but their installed R-value is not sufficient for many locations.

To achieve the recommended R-value in most locations it is necessary to use one of the bulk insulations - fibreglass or rockwool batts, wool batts, or foam boards or sheets. These are installed between the wall studs, and should be cut carefully to avoid gaps between insulation and framing. If using fibreglass or rockwool batts, special wall batts are available which have extra stiffening to help keep them in place.

Where the external cladding may permit water entry, for example from wind driven rain, a perforated foil or breather paper should be secured between the outside of the studs and the cladding to prevent the bulk insulation from getting wet. This is the case for weatherboard and similar constructions. (Figures 5 & 6)

In brick veneer construction, it is important that the bulk insulation is held positively in position so that it will not come in contact with the external bricks. This may be achieved by fixing a nylon or polypropylene string with nails or staples across the space between adjacent timber studs, forming a reliable means of holding the insulation in place, or by using a perforated foil or breather paper secured to the outside of the studs to provide the mechanical support. This is not a vapour barrier. (Figure 7)

Where RFL is used, it is necessary to leave at least a 25 mm air gap on either side of the foil for optimum performance, giving an R-value of approximately R1:0. This is difficult to achieve where cladding is secured on the outside of the frame, as one surface is likely to be in contact with the outer cladding. A well fitting laminate will form a vapour barrier. Generally vapour barriers are not required and in this case a perforated reflective foil sarking or breather paper should be used.

Cavity Masonry

Cavity masonry walls consist of two "leaves'' of masonry (brick, stone, etc.) separated by a cavity approximately 50 mm wide. The purpose of the cavity is to ensure that wind-driven rain does not penetrate to the inner wall.

Cavity masonry walls can be insulated during construction by installing a layer of foam board against the inner layer of bricks. Injected foams or specially treated loose fills (ie. waterproofed granulated rockwool), can be used in some situations. However, at the time of writing, very few local councils will approve of filling the space within cavity brick walls with insulation, unless evidence is provided from a manufacturer that no moisture can transfer through the insulation to the inner layer of bricks.

Vapour barriers

Vapour barriers are required in walls in cold climates, where extensive heating is being used or where unflued combustion heaters are used as the main form of heating. Generally an RFL, thick plastic sheeting or foil backed plaster board is used to provide the vapour barrier

In these cases, the vapour barrier should be installed on the room side (or warm side) of the bulk insulation, to prevent condensation forming within the bulk insulation. Condensation in the insulation reduces its effectiveness, and may damage the frames and walls.

In hot areas, where air conditioning is used, the vapour barrier should be installed on the outside (warm side) of the bulk insulation.

Installing Insulation In Floors

For a typical uninsulated house with a suspended floor, over 20% of heat gain in summer or heat loss in winter can pass through the floor. Insulation of the floor should be considered, but the argument for insulation is less clear than for ceilings and walls, because of cost and other factors.

In temperate climates it may only be necessary to enclose the sub-floor area (underside of the house) to reduce heat loss and heat gain, either by continuing the walls to the ground or by installing a ceiling under the floor.

Timber Floors

Timber floors must be elevated above ground level to comply with building regulations. The underside of the house should be enclosed, but provision for sufficient ventilation needs to be made to keep the under-floor space dry and reduce white ant attack. Floors built in this way that are carpeted are likely to have good resistance to heat loss or heat gain.

Common materials used for insulating under timber floors are RFL, insulation batts, and foam boards. An RFL is usually installed between the floor joists and the floor boards. Insulation batts and boards are usually installed between the joists and may need some form of mechanical support underneath, ie wire, cord or fishing line. It is a good idea to install the insulation so that the timber flooring can be inspected for white ant attack.

Concrete Slab

Concrete slab on ground floors, in cold climates, or where floor heating is used, require perimeter insulation. Generally polystyrene boards or aerated concrete blocks are used against the vertical edge of the slab. Depending on the severity of the climate, the insulation may need to penetrate 1 - 2 metres into the ground. (Figure 12). In cold climates, suspended concrete slabs should be insulated in a similar way to timber floors.

Precautions When Installing Insulation

Insulation should be installed according to Australian Standard AS 3999. To ensure that the insulation is installed properly from a fire safety point of view, two factors need to be addressed:

(1) A gap of at least 25mm should be left around hot objects such as down light fittings, extractor fans, and flues from a gas heater or a wood stove. Where loose fill insulations are installed a suitable barrier should be employed to hold the insulation away.

(2) Unless approved by a licensed electrician, insulation should not cover lengths of electrical wiring greater than 150 mm. Electrical wiring heats up when conducting electricity. Insulation may prevent this heat from escaping and overheating may occur. Where covering of the wiring has not been approved by an electrician, wiring should be kept clear from the insulation. For example it can be secured on top of the ceiling joists, suspended above the insulation, or suitable 'spacers' can be used to ensure that the wiring is not covered. Refer to Australian Standards AS 3999 and AS 3000 for correct installation details.

Also, where fibrous insulations are installed, it is recommended that the installer wear long sleeves and trousers, gloves, and goggles, and that a respirator or face mask is used to reduce the inhalation of the fibre or dust in a ceiling.