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What is Roof Insulation?

Roof insulation is the provision of insulation in the roof space in order to prevent heat loss through the ceilings of the living spaces below.
The method and type of insulation you use in the attic depends on whether the attic is to be used as a living space or not.

If the attic is an unused space, i.e. a 'cold roof', the insulation is applied at the ceiling level. The simplest way of doing this, and if the thickness of the insulation layer is not of any concern, is to roll out fibrous insulation (i.e. glass fibre, rockwool, sheep's wool, etc.) between the joists with a second layer at right angles. You should be looking to at least achieve the Building Regulations standard(0.16 W/m2K) which requires 250 - 300 mm (10-12") of insulation. Other choices for materials with a similar level of insulation include blown fibrous insulation and cellulose fibre insulation, both of which are blown into place through a pipe. Make sure that you still have access to any tanks, pipework etc. by installing a walkway from the entrance to the attic to the water tank, or any other appliances that you may require access to, before laying insulation

If the attic is to be used as a living space, then the insulation goes on the slope of the roof, i.e. between and on top of the rafters. In this case, the space you have is limited by the depth of the rafters so you will need to use a material with a low thermal conductivity to achieve a U-value of 0.16 W/m2K, as per the Building Regulations. If there is an older, non-breathable felt in place, then a gap of 50mm should be left between the insulation and the felt to allow for ventilation between the insulation and felt. The traditional types of insulation used are semi-rigid and rigid roof board insulation. If there is some space outside of the living space within the roof, then this should be adequately insulated at ceiling level.

If you have an existing flat roof, insulation can be applied externally on top of the existing roof and covering with a waterproof roof covering. A flat roof may also be insulated internally with an insulated dry lining board. A vapour barrier should also be applied underneath this new layer of insulation. On a new flat roof with concrete slab, insulation boards or sheets are laid under the roof finish, on top of the concrete.

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