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Insulation is the key to making an energy efficient home. It is responsible for trapping heat within a building allowing much lower amounts of fuel and energy to be used to maintain a comfortable and safe living environment. Some of the biggest savings in carbon emissions and running can be made by properly insulating a build.

Insulation standards are generally specified by 'U-value'. This is a measure of the rate of transfer of heat through the materials of the building. The lower the U-value, the better the insulation. This measure may seem complicated, but it is well understood by designers and provides an easy at a glance measure of how effective a material is. The value is often calculated by specialist engineers.

Types of insulation

Batt insulation is flexible blanket-type thermal insulation, often used as insulation between studs or joists in frame construction. It is also used as an acoustical material or a component in sound-insulating construction. Usually made from rock, slag, or glass fibers. Sometimes has a vapor barrier on one side or is entirely enclosed in paper with a vapor barrier on one side.

Common insulating materials generally fall into one of three categories: foam, wool and block insulation. Each has their own advantages and disadvantages.

Insulation R values and U values

U value is the amount of thermal conductivity. R value is the reciprocal.

The higher the R-value of an insulation product, the higher the insulation - think of 'resistance value'.

See also R values and U values page >

Types of insulation


Foam based insulation is often mixed on site and sprayed into the cavities of a building to form an insulating barrier. The U-value of foam varies depending on the thickness of the foam 25mm has a U-value of 0.877/M2 with 75mm having a U-value of 0.293/M2.

Insulation Advantages of insulating foam:

Disadvantages of insulating foam:


Solid block insulation is usually formed from fibrous materials such as fibreglass, rock wool and wood fibres or from plastics such as expanded polystyrene. 50Mm of expanded polystyrene has a U-value of 0.48 compared to polyurethane's 0.45 U-value for 38mm.

Advantages of solid block insulation:

Disadvantages of solid block insulation:


Wool based insulation consists of two main types mineral based (fibreglass) and natural (sheep's wool). 150Mm of sheep's wool insulation has a U-value of 0.23/M2 compared to glass wool's 0.25/M2 Advantages of wool based insulation:

Disadvantages of wool based insulation:


Other materials such as recycled paper are also used for insulating. Excel Building Solution's Warmcel insulation is made from 100% waste newsprint. It has been successfully installed in more than 1.2 million homes in the UK alone! It is an alternative to blown fiberglass or batt insulation.

Where to insulate


Walls account for over a third of all heat lost from a building. Insulating walls allows them to retain more heat as well as protecting them from cold damp conditions.

External walls can be insulated by either adding coatings made of various materials to the outside and inside of solid walls or by filling the gap in cavity walls with an insulating foam. When a cavity wall is insulated it can save an extra 15% over a standard cavity wall. This is equivalent to 750KG of CO2 per year and around 90GBP on fuel bills.

Solid walls benefit greatly from internal and external insulation, internal insulation can save up to 300 GBP a year with a carbon reduction of 2.4 tonnes, External insulation while more expensive to install will save another 300 GBP and around 2.6 tonnes of CO2 a year. Ideally external walls should be insulated to a U-value of 0.25W/m2K for maximum efficiency.

Internal walls are often more lightweight in construction then external walls. These can be insulated using either wool type materials, foam or solid insulating blocks such as expanded polystyrene. Adding heat insulation to internal walls will also allow sound to be absorbed. The aim should be to achieve a U-value of 0.45W/m2K which is possible using 100mm of insulation or less.

Using wallcoverings and wallpaper, and panelling

Layers of material add insulation.

Sempatap Thermal is a walpaper underlay and an Energy Saving Trust 'recommended product'. Also Polifoam wallpaper underlay improves the heat insulation of cold walls.

Cork wallcovering is also a very good insulator and a natural product. This is often used in bathrooms.

See the Wallcoverings article for more information.


Floors should be insulated to prevent draughts and air leaks from forming. Timber floor boards can be insulated by lifted them up and laying mineral or natural wool supported by a fine mesh underneath. Edges and gaps should then be sealed using a silicon based sealant available from most home improvement stores. Care should be taken to ensure that underfloor air bricks are not blocked as these are essential to prevent wooden floorboards from rotting.

The plugging of excessive gaps will result in savings of around 15GBP and 120kg of carbon emissions. Underfloor insulation will save around 45 GBP and 350 kg of carbon emissions per year. Both methods are cheap to install costing around 100GBP-150 if done by the DIY enthusiast. A good U-value to aim for when dealing with floor insulation is 0.20W/m2K.


Hot water systems that are uninsulated will also lose energy. Fitting a hot water jacket to a storage tank will reduce the amount of heat lost by up to 75%. If a jacket is fitted it should be at least 75mm thick, if not a new one should be installed. Exposed hot water pipes should also be insulated with a foam covering available as tubes from DIY stores. The cost of both these jobs is low but they can save a lot of energy saving about 150kg of CO2 by using a hot water cylinder jacket and about 60kg of CO2 with pipe insulation.

Air and roof insulation

Hot air rises through a structure before finally leaving the building through the roof. This makes the roof insulation the last line of heat trapping. Due to roofs being unoccupied in most buildings this allows the thickest forms of insulation to be used. Roofs should be insulated using natural or mineral wool of with a minimum thickness of 270mm. Roofs insulated to this level will save around £110 a year on heating bills and nearly 1 tonne of CO2 per year.

Roofs should be ideally insulated to a U-value of 0.13W/m2K.

Standards required by UK Building Regulations have recently risen. In 2006 thermal efficiency standards for loft insulation improved from a U-value (thermal conductivity) for the sloping part of a roof, from 0.3 W/m2.K (Watts per metre squared kelvin), to 0.2 Wm2.K. This is a minimum value. Remember that lower figures are better.

This means you will now need about 130 mm of foam insulation instead of 75 mm. Most UK homes only have about 25 mm insulation. Our recommendation is 270 mm.

Insulation allows the construction of an energy efficient building. The more heat that is trapped within a building the less fresh fuel needs to be burned to maintain a comfortable living environment. While the cost of installing insulation varies it will quickly pay for itself, usually within a few years.

Talk to your local council's Building Regulations department to see what is recommended. Most councils have detailed guides to insulation and other energy saving methods.