Fitting cavity wall insulation

Last updated Wednesday 30 April 2008

Mind the gap!

This is one injection you don't have to be afraid of. Fill the space between the two layers of brick in your walls and more warmth stays in the house where you want it.

If your house was built after 1930, you probably have cavity walls. Walls are the number one culprits for letting our heat escape - they leak around 33% of the heat lost in the average home - so filling the cavity with an insulating material is one of the most effective ways to save up to 15% of your energy bill and cut CO2emissions at home. Also money might be available which can greatly reduce the costs of installation and people on certain benefits can have it installed for free.

An average house could save 750kg of CO2 a year - that saves almost twice as much CO2 as swapping your petrol car for an LPG model - and about 90 on heating bills. The bigger your house and the larger your heating bill, the bigger the potential savings.

Homes built after around 1995 have cavity walls which were filled during construction. If you're unsure then call an installer who should be happy to come around and tell you whether you have unfilled cavity walls.

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Photo: Fitting cavity wall insulation

Saves 750kg of CO2 a year

233 Bloomers are doing this

CO2 reduction 2 out of 5

Cheapness 3 out of 5

Popularity 3 out of 5

Cost 500, 5 year payback

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How does it work?

Pub Fact

  • Only 37% of homes with cavity walls have cavity wall insulation
  • If everyone in the UK did this, CO2 emissions would nosedive by over 6m tonnes - enough CO2 to fill Wembley Stadium 800 times
  • Uninsulated cavity walls cost Brits 770 million a year - that's enough energy for 1.5 million homes a year
  • Foam cavity wall insulation is made from the chemical formaldehyde and urea: a substance found in urine
  • Insulating cavity walls provides one of the largest energy savings in the home, reducing heat loss through the wall by up to 60%

Most homes built after 1930 have two layers of exterior brick wall with a space in between (the cavity). A professional installer will drill holes in the wall and inject insulating material inside. This filler traps heat and stops it escaping through the walls.

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How will it make a difference?

If we filled all the cavity walls in Britain, we'd save over 6 million tonnes of CO2 a year: that's 1% of Britain's entire CO2 emissions. Only 1%? Well, it may not sound much, but it's potentially a larger saving than any other single insulation measure.

In addition to stopping heat getting out, insulation stops heat getting in during summer, which means less need for energy-hungry fans or air conditioning.

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How do I do it?

  • Find out whether you have cavity walls by checking the pattern of the bricks. Solid walls have shorter bricks running across the cavity
  • Choose a material from the Energy Saving Trust's recommended products. The most common are plastic foam and polystyrene beads
  • Find out whether you're eligible for a grant or offer via the Energy Saving Trust's website, or call them on 0800 512 012. If you receive benefits, you may be entitled to free insulation
  • Choose a contractor accredited through the Cavity Insulation Guarantee Agency. This ensures the insulation will be guaranteed for 25 years against rain and other damage
  • For a small semi-detached house, the process takes a minimum of two to three hours, so be cautious of contractors offering to do it any faster

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What's the debate?

No one seriously disputes that cavity wall insulation is a big winner in the battle to reduce CO2 emissions from the home. It's not suitable for a tiny minority of houses on exposed, windy sites but your installer will be able to tell you if that's the case.

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What's stopping me?

"I'm planning to sell my house - why should I waste the money?"

It's not a waste. To sell your home you need to provide an Energy Performance Certificate. This will score your home for energy efficient between an A and G rating. Most British houses only score a D or E, so cavity wall insulation will bump up your home's efficiency rating, potentially adding value to your property.

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Anonymous, Sheffield 2010-01-06

I used to have letter box that flapped open if there was a strong breeze. It took ages to get a new one but I would recommend it as my hall way . now ikeeps lovely and warm. Best bet is not to have a letter box at all but I would need a new door

Simon Benson 2009-03-09

I approached my council and got an additional discount on the cost due to some initiative or other (Lancashire county council). It cost me just 99 to have my large 3 bed semi cavity wall insulated due to goverment and council input into the 600 overall cost. this was an absolute bargin and I felt the diference in the warmth of the house (it holds its heat longer, so less heating :)). Highly recommended and in my view, possibly the cheapest money and planet saver you can do.

RH, Painswick 2009-01-29

I used to live in a house built in the 1970s which I had cavity insulated. We were very pleased with the results. We now live in an older property -1930s - which we have had surveyed 3 times. 2 installers said they could not insulate the property because the ties were brick and would cause voidage. Can you suggest how I can procedd as we would like to regain the benefits of insulation.

Gaz@Llantwit, vale of Glamorgan 2009-01-27

Having spoken to a number of reputable installers/contractors, I have been trying to find out whether one particular type of material is better / more efficient than another. Most seem to offer either bonded beads or mineral wool, with the former being slightly more expensive. How do I find out which is better? I've tried searching the web for a comparison, but have failed to find one!

I've also read that having the cavity filled can increase the chance of damp internally. One well know Telegraph journalist has even stated that, because of this, you shouldn't have cavity wall insulation. How much truth is there in this, and therefore what's the risk?

Breadon, Pershore 2008-08-30

My home waas built in 1989 and supposedly had cavity wall insulation when it was built. I was suspicious about this. The local authority has published pictures showing energy loss. My home was not doing well. The contractor drilled a hole to see what was in the cavity and let me have a look. There was nothing there. Have accepted quote and am awaiting installation. He said it wasn't that common but he had come across houses built just 5 years ago that supposedly had cavity wall insulation but in reality didn't.

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Glossary terms used on this page
CO2, or carbon dioxide, is made up of the elements carbon and oxygen. It exists quite naturally in our atmosphere, as part of the carbon cycle. Everyday processes in the plant and animal world both add CO2 to the atmosphere and take it out. However, because it is a greenhouse gas - meaning it affects the temperature of the earth - the exact level of CO2 is important. Burning fossil fuels releases CO2 into the atmosphere, hence the anxiety that extensive use of these fuels is causing climate change.
Cavity walls
A wall comprising two layers of brick or block separated by a cavity (gap). This air space acts as an insulator, but does so more effectively if filled with an insulating material, such as plastic foam or natural materials like wool or recycled newspaper.
Efficiency ratings
All white goods and other household appliances sold in the UK are now required by law to carry a rating indicating their energy efficiency. Goods are graded A to G, with A the most efficient. Information on the EU-wide labelling scheme is available from the government's environment department, Defra.
Emissions are the CO2 (and other greenhouse gases) produced by energy use, usually calculated and stated as an annual tally: also referred to as your carbon footprint. Your personal emissions can be direct - such as the gas you personally use to heat your home or the petrol you burn to power your car - or indirect - meaning the energy use that has gone into the products or services you buy. The latter, such as the emissions caused by the manufacture of your new TV, or the packaging your food comes in, are also referred to as embodied emissions.
Energy efficient
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