External walls

Heat is lost through the floors, roofs and walls of the house. In order to reduce the amount of heat lost through the external walls one of three methods of insulating the wall can be used. The single most cost effective measure is to install cavity wall insulation. Alternatively if the wall does not have a cavity, or it is not suitable for filling, then either an external wall insulation system can be applied, or an internal insulated dry-lining. Each method is described briefly below.

Cavity Wall Insulation

The majority of masonry cavity walls built since the 1930s are suitable for filling with cavity wall insulation. Insulation, either polystyrene beads or mineral fibre are blown into the wall cavity through a number of holes drilled in the exterior of the wall. Once the insulation is installed these holes will be filled up with mortar. Before the insulation is installed a survey should be carried out to confirm the wall is suitable for insulating and if any defects are identified these should be corrected first. The installation should only be carried out by an approved company using an approved system under the British Board of Agrement (BBA) approvals system. A guarantee is available via the Cavity Insulation Guarantee Agency (CIGA).

Internal Wall Insulation

Where the walls of the house are either solid masonry or a cavity wall is not suitable for cavity wall insulation then it can be cost effective to insulate the internal surface of the wall. This is most often done by applying an insulated dry-lining, a layer of plasterboard with a rigid insulation material bonded to it. This is most cost effective when the existing plaster is being renewed, or existing services or fittings, such as kitchen units are being replaced. Applying the insulation internally has the benefit of ensuring that the wall surface warms up quickly helping to improve thermal comfort. It has the disadvantage of reducing the size of the room by the thickness of the insulation. The insulation layer can be up to 50mm thick. This also requires all electric sockets, switches and pipework to be relocated once the insulation work is complete.

External Wall Insulation

An alternative to installing insulation on the internal wall surface is to install it externally. The design and installation of external wall insulation is a specialist job, and advice should be sort from an approved Company over the most appropriate system for a job. It is generally the most expensive of the three methods to insulate a wall, but can be cost effective where replacement of the render is being carried out or a major refurbishment is planned. External wall insulation consists of a layer of insulation (either rigid or mineral fibre) fixed to the external surface of the wall with a variety of decorative finishes applied to the insulation. Where these changes will affect the appearance of the building the local Planning Office must be consulted first.

Further Information

• CE16 - Cavity wall insulation in existing housing
• CE17 - Internal wall insulation in existing housing - a guide for specifiers and contractors
• CE58 - Refurbishing Dwellings with Solid Walls: A summary of Best Practice
• CE83 - Energy efficient refurbishment of existing housing
• CE97 - Advanced insulation in housing refurbishment
• GPG171 - Domestic Energy Efficiency Primer
• GPCS418 - Energy efficient refurbishment of existing housing - case studies