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Cavity wall

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About a third of all the heat lost in an uninsulated home escapes through the walls.Heat will always flow from a warm area to a cold one. In winter, the colder it is outside, the faster heat from your home will escape into the surrounding air.


Most houses built from the 1990s onwards have wall insulation to keep the heat in, but if your house is older than that it may not have any wall insulation. If this is the case then you may be heating the outside air, instead of just heating your home. Most types of wall can be insulated in one way or another. If you have a typical house with cavity walls, you could save up to £140 per year in heating bills just from insulating the walls.


The first thing you need to find out is what sort of walls you have.

        Cavity and solid walls


Houses in the UK mostly have either solid walls or cavity walls:


           A cavity wall is made up of two walls with a gap in between, known as the cavity; the outer leaf is usually made of brick, and the inner layer of concrete.


           A solid wall has no cavity; each wall is a single solid wall, usually made of brick or stone.

        Working out your wall type


If your house was built after the 1920s, it is likely to have cavity walls. Older houses are more likely to have solid walls.


If you can see the brickwork on the outside of the house, look at the pattern of the bricks. If your home has cavity walls, the bricks will usually have a regular pattern like this:


If your home has solid walls, the bricks will have an alternating pattern like this:



If the brickwork has been covered, you can also tell by measuring the width of the wall.  examine a window or door on one of your external walls. If a brick wall is more than 260mm thick then it probably has a cavity; a narrower wall is probably solid. Stone walls may be thicker still but are usually solid.

        Non-standard wall types


If your house is a steel-frame or timber-framed building, or is made from pre-fabricated concrete different rules apply for insulation.


Generally these houses don't have a cavity to fill, but it may be possible to insulate them in the same way as a solid wall. However, you may need a specialist company to insulate a non-standard wall. For further advice or to find an installer who can help you, contact the National Insulation Association.


        Cavity wall insulation


If your home was built after 1920, the chances are that its external walls are made of two layers with a gap or cavity in between. Cavity wall insulation fills that gap, keeping the warmth in to save energy. It can also help reduce condensation inside the house if this is a problem on your external walls.

        Is cavity wall insulation suitable for your home?


Your home will usually be suitable for cavity wall insulation if it meets these criteria:


              Its external walls are unfilled cavity walls.

             Your cavity is at least 50mm wide.

             The masonry or brickwork of your property is in good condition.

             It is more than 10 years old (most newer houses will have insulation already).

             The walls are not exposed to driving rain.

        Are your external walls accessible?


Cavity wall insulation is blown into the cavity from the outside of a house. Every part of the wall must be filled with insulation, so it's important that the installer can reach all your external walls.


If your home's external walls are joined to another house, the installer will need to insert a cavity barrier to contain the insulation, so your neighbours aren't affected.


        What if your house is damp?


If you have any damp patches on your internal walls then they should not be insulated until the problem is resolved. Speak to a builder who specialises in damp prevention.


        How is insulation installed?


To insulate your cavity walls, the installer drills small holes around 22mm in size at intervals of around 1m in the outside wall of your home. The installer then blows insulation into the cavity using special equipment. Once all the insulation is in, the installer fills the holes in the brickwork so you'll barely notice them.


Filling cavity walls is not a job you can do yourself, you will need to employ a registered installer. A professional can do the job in around two hours for an average house with easily accessible walls. It shouldn’t make any mess.


        What is insulation made of?


Cavity wall insulation can be made from three types of material: mineral wool, beads or granules, or foamed insulants.


All three are manufactured according to British standards. Foam insulation systems should be certified by the British Board of Agrément and installed according to strict guidance laid out in the associated certificates.