Installing insulation in a new dwelling or adding insulation to an existing building can make a significant difference to the comfort and energy performance of a home, but it is vital that the insulation is installed correctly.
To install insulation without compromising its effectiveness, you need to consider a range of issues such as:
- thermal bridging;
- vapour barriers;
- air-gaps; and
- physical handling of the different types of insulation.
The building frame can act as a thermal bridge, particularly in cold climates, conducting heat and allowing it to bypass otherwise effective insulation. Metal framing is a particular problem because of its high conductivity. The presence of the frame reduces the overall insulation value, as the frame can constitute up to 15% of the wall, ceiling or floor surface. To help overcome the effect of thermal bridging, install isolating strips such as Thermatape™ between the metal frame and cladding, which must provide a minimum Material R-value of R0.20.
Use vapour barriers to help protect the building from condensation:
- in high humid (tropical) climates;
- in cool climates where the difference between indoor and outdoor temperature is significant;
- in roof spaces with a low ventilation rate (e.g. cathedral or raked ceilings);
- in situations where a high amount of vapour is generated and not exhausted; and
- on the underside of metal roofing, to minimise the likelihood of condensation and corrosion.
Install vapour barriers on the warm side of the insulation:
- in cold climates, on the inside of the insulation (directly above the ceiling lining and next to the internal wall lining) and in warm climates, on the outside of the insulation.
It is important that you check the cladding manufacturer’s specification relating to the characteristics the wall wrap material employed should possess.
- Ventilate the roof space where possible to allow built-up heat to dissipate. Even in cooler climates, a minimal amount of ventilation is desirable to allow built-up moisture to escape. Air gaps along the ridgeline or between tiles often provide sufficient ventilation. Gable or eaves vents may also be used.
- Ventilated roof spaces in high humid (tropical) climates under metal roofing can result in excessive condensation within the roof space at night. You can help prevent condensation dripping off the underside of metal roofing onto the ceiling by installing reflective building membranes similar to that used under roof tiles, or using a foil-backed building blanket such as Permastop® Building Blanket or Permastop® Tropic Building Blanket (anti-condensation blanket) under the metal roof, or closing the vents at night to prevent night air from entering the roof space.
- Keep roof spaces weather-tight and vermin proof.
- Avoid leaving gaps between each piece of insulation. Even a small gap can greatly reduce the insulating value. Fit batts snugly and do not leave gaps around ducts and pipes. Tape up holes and joins in reflective insulation. Make sure the ends of multi-cell and concertina foils are well sealed, and ensure that corners of walls, ceilings and floors are properly insulated as these are areas where heat leaks most often occur.
- For safety reasons, minimum clearances must be left around hot objects, such as flues from fires, recessed downlights and their transformers.
- Wall insulation must butt into door and window frames. In cold climates, metal frames around glazing should have thermal breaks to reduce heat loss.
- Insulate internal walls between the house and uninsulated spaces such as garages and storerooms.
- Do not compress bulk insulation as this reduces its effectiveness. Ensure there is sufficient space for the insulation to retain its nominal thickness.
- Keep moisture away from bulk insulation, or its performance will be reduced (water resistant types are an exception). Use a vapour barrier where there is a risk of condensation.
- Restrain bulk insulation in cavities so it does not come into contact with the porous outer skin of the wall.
- Potential problems to be aware of include the overheating of electrical cables, dampness (if the insulation is absorbent) and moisture transfer across the cavity by capillary action.
- Maintain an air space of at least 20mm next to the shiny surface of reflective insulation. If this is not accomplished, the insulating properties are reduced.
- Dust settling on the reflective surface of insulation greatly reduces its performance. Face reflective surfaces downwards or keep them vertical.
- Reflective foil insulation should not be placed on top of ceilings or ceiling joists, nor under floors, as it is electrically conductive. Any such insulation must also be secured with non-conductive staples.