Roofs

Heat is lost through the floors, roofs and walls of the house. In order to reduce the amount of heat lost through the roof, the roof should be insulated. Generally roofs are either pitched with an accessible loft space or a flat roof with no loft space.

Pitched Roofs

Insulation is generally placed between the ceiling joists covering all of the ceiling area. If the loft space has a cold water storage tank, then insulation should be placed over and around the tank, but not below it to prevent freezing and burst pipes. All pipes in the loft space should be insulated and electric cables routed above the insulation to prevent them overheating. The insulation should be at least 250mm thick and preferable laid in two layers, one between the ceiling joists and one across the top. This helps to further reduce the heat lost by the roof structure. To ensure the loft space stays free of condensation, a free flow of air is required above the insulation. To maintain this flow of air special trays should be installed at the point where the walls and roof meet, which allow air to pass over the insulation. Finally, don't forget to insulate the loft hatch and draught proof it as well.

Flat Roofs

Insulation in a flat roof maybe within the roof structure, often called a 'cold deck', or placed above the structure as part of the roof finish, referred to as a 'warm deck'. It is most cost effective to provide or replace the insulation in a flat roof when the roof covering needs renewing. With a cold deck construction it is important to maintain a flow of air above the insulation to remove any moisture. Due to the problems of doing this satisfactorily it is often simpler to provide insulation above the roof structure and make the roof a warm roof. The type of insulation used should be a rigid board material, such as extruded polystyrene and it should be at least 100mm thick.

However, the design of the roof may limit the total thickness of insulation that can be installed. If a flat roof is being converted to a pitched roof, then the roof should be insulated to the same standard as a new building. Minimum standards for the thickness of insulation to a new or refurbished roof are set within the Building Regulations.

Further Information

• CE83 - Energy efficient refurbishment of existing housing
• CE97 - Advanced insulation in housing refurbishment
• GPG296 - Refurbishment site guidance for solid-walled houses - roofs