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    Cavity wall insulation

    In homes without insulation it is estimated that a third of all heat lost escapes through the walls. Many houses built since1920 are constructed with exterior walls made up of two skins – an outer wall built from brick and an inner wall built from block – with a narrow gap of about 50mm between them. To dramatically reduce heat loss the cavity between double-skinned walls can be filled with an insulating material.

    Cavity wall

    Solid wall

    Holes of about 25mm diameter are drilled through the mortar of the outer wall and then the insulation is injected into the cavity from outside. It is mess free and quick to install; the whole process taking around two to three hours for an average sized property. Once the installation is completed the contractor will plug all the injection holes with mortar, matching it as closely as possible to the colour of the existing mortar.

    But first it needs to be established whether your property is suitable for this type of insulation. If you have a traditional brick built property there is a simple test you can carry out to see if it has been built with cavity walls. This involves checking that no brick ends (headers) appear in the wall, for this is an indication of a solid wall construction. Other influencing factors include:

    • Living in an upper story flat. The insulation material fills the cavity from ground level, therefore if your neighbours below are not in agreement, the process can’t be carried out.
    • The cavity has already been filled. Since 1982 most houses have been built with cavity wall insulation.
    • The property has a problem with damp. This must be remedied before cavity wall insulation is installed.
    • Structural problems such as cracking and flaking brickwork or the erosion of the pointing also need to be made good. These problems are often indicators of damp.
    • Rubble or other debris at the bottom of the cavity and mortar on the wall ties can also be a problem, for it creates a bridge allowing damp to penetrate from the exterior wall to the interior.
    • A cavity width of less than 50mm is unsuitable for this form of insulation.

    Cavity wall insulation is suitable for terraced and semi-detached houses even if the neighbours don’t wish their property insulated, as the contractor can install a cavity barrier at the party wall between two properties.

    Three types of insulating material are used in cavity wall insulation: mineral wool, polystyrene beads and Urea Formaldehyde (UF) foam. Tests have shown all three materials share a similar insulation value.

    Although a relatively simple operation, cavity wall insulation is specialist work that needs to be carried out by trained technicians with the expertise and equipment to ensure the insulation is filled to the correct density. Look for a contractor whose work is covered by CIGA (Cavity Insulation Guarantee Agency), as the work will be guaranteed for 25 years.

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