Download a condensed version of the wall insulation advice here (pdf).
For most households, heating your home is the largest part of your energy bills and the largest component of your energy use. By insulating your home you reduce heat loss and hence reduce your bills, your energy use and carbon emissions which contribute to climate change.
It is always recommended that you improve your home's insulation as much as possible before installing low-carbon heating. Savings will be immediate even with your current heating system, your low-carbon heating will not need to be so large and hence likely to be less expensive, and it will also immediately improve the comfort of your home.
Insulation reduces the transfer of heat either into or out of your house throughout the year. This means in the winter the heat will be retained in your home for longer and in the summer your house will stay cooler. Also if you have problems with condensation and mould on cold surfaces, insulation will help because the surface will be warmer.
The amount of heat lost through different parts of the building fabric (walls, roof, windows etc.) varies with the shape and structure of the house and how much insulation you have installed already. Here is a tool which can give you a rough idea for your house.
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In simple terms the ‘U Value’ of a structure, such as a wall, roof or window, tells you how much heat you can expect to lose through it. The structure can have lots of layers and the U-value describes the performance of the whole. Low values are good.
A solid brick wall is likely to be around 1.5. After insulation it could be 0.3 or even lower – a reduction of over 80%. Filling a cavity wall will reduce heat loss through the walls by a factor of two or more.
Cavity walls are typically made up of an external wall made of brick, an internal layer of brick or concrete block and a gap or cavity between them of approximately 50mm (2 inches). Filling this gap with insulation decreases the amount of heat escaping through the walls, making the house warmer and reducing the amount of fuel required to maintain a comfortable temperature.
If you have cavity walls, insulating them is usually the most effective energy saving measure you can take. The insulation is inexpensive, and takes only a few hours to install. It is blown into the cavity from the outside through small holes drilled into the brickwork. All cavity wall installations are backed by a 25 year independent guarantee from the Cavity Insulation Guarantee Agency (CIGA).
The first step is to find out when your house was built. If your house was built after 1920 there is a good chance it will have a cavity.
The next step is to look at the style of the brick work. Typically houses with cavity walls have a regular pattern or bricks using the length of the brick, houses with solid walls show a mix of length and ends of bricks.
The third way is to measure the width of the wall (this is the best method if your wall is covered). The easiest place to do this is at a window or a door on one of your external walls. If the walls are more than 28cm (11’’) thick then it is likely it is a cavity wall. A narrower wall is probably solid (although remember that stone walls can be even thicker!).
NB: A timber frame wall with brick cladding can have the same external appearance as a cavity wall. A qualified inspector can confirm the type of wall you have.
Now go to Insulating Cavity Walls or Insulating Solid Walls