Loft Insulation for Rafters

Benefits

• The main benefit of all insulation, including that applied between loft rafters, is lower energy bills. In cool climates, insulation prevents heat generated by the central heating system from escaping by providing an air barrier. This also means that in warmer climates, it helps keep the house cool by stopping outside heat from entering the home. Energy bills are thus lowered, because in an insulated home either less heating is required or less air conditioning -- a function that uses a lot of electricity -- is needed.

Batts

• The most common form of insulation installed in the loft rafters is fiberglass batts. These are pre-cut lengths of woven fiberglass – sometimes called blankets – that can be trimmed to fit particular spaces, and affixed to the ceiling with staples. The have an average R-value – the measure of a material’s insulating effectiveness; the higher number the better – of between 3.14 and 4.3 per inch. They are cut to fit the spaces between rafters and stapled to the rafters themselves. They are naturally fire-resistant, but may require a vapor barrier if moisture is a problem in the loft.

Foam

• A second popular choice for insulating the rafters of attics is sprayed-on foam. Manufactured from polyurethane or similar polymers, sprayed foam is installed using a spray gun or pressurized-air machine. The liquid foam expands and hardens in place, providing an effective air and vapor barrier that conforms to the shape of the rafters. It has an average R-value of 6.25. It is, however, more expensive to install than fiberglass batts, not least of all because it usually requires professional installation or, at least, the purchase of specialized equipment.

Precautions

• The loft provides crucial "breathing space" for your home so do not cover any duct work with insulation. Furthermore, you may need to install vent baffles between the insulation and the roof to ensure that there is sufficient air flow through the loft. This will help prevent moisture build-up, which can lead to mold and mildew forming. Check the local building codes for vent requirements.