Action Surrey: Surrey's Low Carbon Community

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Insulation: Cavity Wall

Install cavity wall insulation FREE and save up to £255 a year**

Approximately 1/3 of the heat from a home is lost through the walls. Insulating the walls of your house is the equivalent to wrapping it in a thermal blanket. Heat always flows from a warm area to a cooler area and insulation between or on the walls helps slow this transfer of heat from the warm air inside the property to the cooler outside air. Cavity wall installation is quick and can take only a couple of hours depending on the property. It is almost always done from the outside to minimise disruption.

How much could you save?

England, Scotland and Wales

 DetachedSemi-detachedMid terraceBungalowFlat

Fuel bill savings per year






Typical installation cost (if no grant applies) 






Payback time

                               5 years or fewer  

Carbon dioxide savings (kgCO2/year)

1,040 kg

620 kg

380 kg

420 kg

290 kg

Is your home suitable?

  • If your property was built between 1920 – 1990 it’s likely to have uninsulated cavity walls
  • Your walls must have a cavity of at least 50mm wide, and is clear of rubble
  • The brickwork of your property is in good condition
  • The brick pattern will show all the long side of the bricks (see below for example)

Note: If you are renting you will need your landlord’s permission before any work can be undertaken. 

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.

Solid walls need external or internal wall insulation, more information can be found here

Grants & Subsidies

Subject to your property and circumstances, there can be grants available to help towards the cost of installing cavity wall insulation - with up to 100% grant funding available, to homeowners and those renting privately**. You will require an unfilled cavity.

For more information, head to our Financial Support page or contact Action Surrey on 0800 783 2503 or email 

Alternatively, fill out our enquiry form online to obtain a survey and no-obligation quote.

Enquire now

*All figures are taken from the Energy Saving Trust April 2019 figures

**Subject to availability, eligibility and survey