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    Insulating the rafters

    Summary: Learn how to insulate the rafters.

    There two main reasons for insulating the roof: to save heat energy and when converting the attic into an additional room.

    When insulating between the rafters in the attic, firstly ensure there isn't a leak in the roof. Check it out to avoid complications at a later date. This is especially important, as leaks are hard to spot after insulation has been installed.

    There are two types of insulating material designed for this job: blanket insulation and semi-rigid fibre insulation batts.

    Another factor to consider is condensation caused by the underside of the tiles becoming very cold. This problem can be overcome by providing adequate ventilation.


    • To ensure there is adequate ventilation you need to create a 50mm (2in) space between the insulation and the tiles. This can achieved by fixing lengths of treated timber 50mm (2in) thick to the inside edges of each rafter. The timber should be screwed to the rafters as hammering in nails could dislodge the roof tiles.
    • Measure the width of the gap between the rafters and cut the insulation material to the correct size. Fit it between the rafters maintaining the 50mm (2in) gap you've created between the roofing felt and the insulation.
    • A vapour barrier should be included on the warm side of the insulation. Some blanket insulation material has a foil backing which when fitted with the foil facing into the loft acts as a vapour barrier. If using un-backed insulation blankets a vapour barrier can be created by stapling polythene sheeting to the rafters over the blanket.
    • Having completed fitting the insulation material and vapour barrier, depending on what the roof space is to be used for, a finish material can be fixed to the rafters. This could take the simple form of building paper stapled to the rafters allowing different sheets to overlap by at least 100mm (4in) and taping the joins with an adhesive waterproof tape.
    • Alternatively, a more solid finish can be achieved by covering the rafters with sheets of plasterboard. Use screws to fix the boards to the rafters, staggering the joints between the boards. Although a little more expensive, plasterboard screws tend to hold the board more firmly in place.

    Fix lengths of treated timber to the inside edges of each rafter to create a ventilation space.

    Fit the insulation material between the battens.

    Create a vapour barrier by stapling polythene sheeting to the rafters over the blanket.

    If required, a solid finish can be achieved by covering the rafters with sheets of plasterboard.

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    Tools Needed
    • Screwdriver
    • Tape measure
    • Staple gun
    Materials Needed
    • Treated timber
    • Screws
    • Foil-backed insulation
    • Polythene sheeting if the insulation has no foil on the back
    • Building paper OR plasterboard
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