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If you are converting the attic area into a living space, there are strict regulations on the amount of insulation required. Rafter depth is an issue, as there is often not enough depth to fit the required insulation — you may need to increase the depth of rafters by adding wood to their undersides. The drywall will probably need to be insulation-backed; framefoil varieties will need to be stapled across the rafters before applying drywall. An air gap is generally required for this, which is achieved by battening of the framefoil — always pay close attention to a manufacturer's specifications. Remember to consider green insulation materials, such as recycled batts.
Using Recycled Batts
Recycled batts are a good alternative to blanket insulation for rafters and walls. They are more eco-friendly, and are often easier to position (blanket insulation can sag before it is secured in place by drywall). Either type may need to be cut to fit the exact space between rafters or studs.
In many cases, a dwarf wall is used to partition the eaves area. This makes a more practical space for positioning furniture and fittings. The area behind the wall is treated as a cold insulated roof even though it is a relatively small space. Insulation is laid at joist level to reduce heat loss from the floors below.
Fix lengths of treated lumber along the inside edge of each rafter right up against the roof felt (Image 1). These furring strips maintain the ventilation gap when non-breathable felt is in place. Even when using breathable felt, it is still good practice to leave this ventilation gap.
If necessary, increase the depth of the fill space by fixing 2 x 2 in (50 x 50 mm) wooden battens along the roof rafters. Screw them into position (Image 2).
Infill the space by wedging the blanket between the furring strips but do not compress the insulation against the underside of the roof (Image 3).
Wedge the insulation in the gaps between the studs in the dwarf wall. A tight fit is required to ensure that the insulation doesn’t fall backward. Nails can be tapped in along the back edge of the studs to prevent this. Alternatively, use a rigid insulation board instead of blanket insulation.
Cover the rafters and the lower dwarf wall with vapor barrier, then staple the sheets to the joists.
Fix thermal drywall to the dwarf wall, butting the boards up against one another (Image 4).
Stagger the joins between subsequent boards to ensure you have complete coverage, and screw boards to the rafters as you go (Image 5).
Excerpted from Do It Yourself Home Improvement
© Dorling Kindersley Limited 2009