Average cavity wall insulation cost

Summary: How much does cavity wall insulation cost, average labour costs and average material costs.

Did you know that up to third of your home's heat is lost through its walls? Filling the cavities between the two outside walls of your property with insulation will significantly reduce your energy costs. The insulation material prevents convection currents within the trapped air thus making air the prime insulator. New buildings often have an insulation layer already built in, usually from rock wool or glass fibre. However, if you have an older property choosing to make the investment of insulating the walls' cavities will more than pay for itself in energy savings and make your house warmer in winter and cooler in summer. You will usually recoup your investment in about three to four years.

Average cost


Average cost



Cavity wall insulation £150 - £500 2012 Get quote

Factors to consider

Firstly you need to check if your house has any cavities to fill. Generally houses built after 1930 and before 1995 have exterior walls built with two layers between which is a small air gap, or cavity, available to fill. If you're still not sure, then you could check the thickness of the exterior wall by measuring either a doorway or window - if the wall is over 30cm thick, the chances are it has been built with cavities. Also if the brickwork has a pattern which is entirely made up of the longer sides of the brick on the outside, with no end pieces, this is another indicator of cavities being present.

You will need to have the wall surveyed and approved by a surveyor prior to any work beginning (all good installers will give you a no-obligation survey). Ensure any companies you use are registered with the CIGA (Cavity Installation Guarantee Agency) and the work is done to British Standard 8208. Membership of the National Insulation Association (NIA) is an indicator of good workmanship. The guarantee given will last 25 years and can be passed on to the new house owners should you move house. Installation should never be attempted as a DIY project.

It is important to check that there is sufficient access to all parts of your exterior walls, as the installers will need to fill each part of all the walls. You may need to speak to your neighbour if your cavity space joins straight onto their cavity; in such cases a cavity barrier can be put in place so the two properties are separated. This can be done by the installer.

The insulating material is blown into the cavity through pre-prepared holes in the exterior part of the wall, using hoses, until it fills the available space. The walls will have holes drilled into them that are about the size of a 10p piece. When the holes are refilled they can be repainted; a close colour match is aimed for, but this is never a guarantee. The work normally takes about two to three hours.

It is essential that your home's ventilation is not affected by this insulation work. Your installer has an obligation to ensure this remains the case. It is worth noting that walls that are particularly susceptible to driving rain may not be suitable for installing cavity wall insulation.

The insulating material is blown into the cavity through pre-prepared holes in the exterior part of the wall using a hose.

Once the cavity is full then the holes are refilled.

Costs to consider

Since this job must be carried out by professionals you will always have the cost of hiring the insulation installer. In order for cavity wall insulation to be installed the brickwork/masonry on your property needs to be in good repair. If it isn't this may be an additional expense. Also if there are any damp patches on the wall they must be attended to before work begins which could be a DIY job or may mean hiring a builder who specializes in damp prevention.

In the United Kingdom grants are widely available from the government and energy companies to subsidise the cost of installing cavity wall insulation. Some people are eligible to have the work done completely free; this particularly applies if you are on certain state benefits. There are plenty of websites that give advice on these subsidies.

There are different types of insulation, which may affect the total price; cellulose (a fibrous material), glass wool and polyurethane foam (which has taken the place of urea-formaldehyde which some people were allergic to).

There are some other positives to come out of this procedure too. Cavity wall insulation should last the lifetime of the house, so will continue to give you energy savings year after year, for as long as you stay in your home. Each year that you have your home insulated could save one tonne of CO2 emissions being released into the atmosphere, making a huge impact on your personal contribution to slowing down climate change.

Cavity wall insulation should last the lifetime of the house.

In the United Kingdom grants are widely available.