27 Apr 2009

On Cavity Wall Insulation

The house I am currently living in was built in 1960. I have long been pondering what exactly to do with it: the choices being the demolish it and rebuild a new, or to renovate it.

It’s got lots of glass. A very sixties house. Even though it’s double glazed to a reasonable standard (mostly aluminium frames), it gets cold and the heating system is barely up to the task of keeping it warm in winter. It will readily burn 20 litres of oil a day in winter on space heating and that translates to something like 150kWh/m2/annum under normal occupancy conditions. Or ten times the PassivHaus standard of 15kWh/m2/annum, now the target of choice for low energy designs.

It has cavity walls — that’s easy to tell because all the bricks are stretchers — but whether the cavity itself has insulation in it I have no idea. So, when researching an article last month about grants for cavity wall insulation, I contacted two agencies who undertook grant work and both said they would send a surveyor out within six weeks. Last night at 8pm, a guy rings and asks if he can come by at 8 am this morning. He actually arrives at 7.22. He’s gone by 7.27, having drilled one hole through the brickwork, found evidence of some polystyrene beading and then announced that “I’d no need to worry because I’d been done already.”

I am left wondering. What was all that about?

I await the visit of surveyor No 2. And more thoughts about the Cavity Wall Insulation Business.

The scheme contact details are as follows. One is run by the Energy Savings Trust, called the Affordable Energy Scheme (Tel: 0800 512012); the other is called the Heat Project (Tel: 0800 093 4050), which is funded by the energy suppliers. They offer pretty much the same thing, which is subsidised cavity wall and/or loft insulation. Anyone can apply for this grant-aided work, which has to be carried out by approved installers, and the rate paid is fixed at £189 which gets you 130m2 of cavity wall insulation or 55m2 of loft insulation – or twice £189 (=£378) if you want both. If your project exceeds these amounts, you are charged pro rata at £4.50/m2. If your project is smaller, then the rate is lower.


  1. What is the purpose and advantage of a cavity wall. Why were they introduced in the first place? What are they still used so widely?

    Wouldn't it be much better to have all the thermal mass (bricks) of the building inside the insulation, rather than having half of it outside?

  2. Markus, I am sure Mark could answer this better, but as I see it, the key words are 'bricks' and 'planners'

    The british love of bricks and the planners' near insistence on using them is at the root of this way of building. Bricks are usually quite porous and the cavity is there to stop moisture/rain from penetrating to the inside of the house as occasionally happens with solid brick walls. It is only recently that cavities have been used to contain insulation.

    Yes, in many ways it would be better to have solid masonry walls (if you want to build that way) with the insulation on the outside, as is commonly done in Europe but then you more or less have to have an outside finish of render. Nothing wrong with that you might say - cheap, waterproof and durable but it doesn't look like proper 'bricks and mortar'

    If you want to see bricks on the outside, the insulation has to go on the inside

  3. "The british love of bricks and the planners' near insistence on using them is at the root of this way of building."

    Goodness how I agree on this one!

    Our painted-brick bungalow is currently receiving some extension work. I want to use Aquapanel Exterior, with slip bricks and then painted to match the rest. Will they let me?! What do you think...?

    It's a joke because we know that the performance requirements would be improved, the environmental impact of the construction is less and the need for skilled labour also reduces. What's astonishing is that the bricks are painted with a heavy white paint - and they specify they HAVE to be London brick! Why?

  4. I find it very difficult to talk about Planning rationally, in part I think because on a day to day basis, what planners do is not very rational. Most people think we need some planning regulation (although vast numbers of fine, sought after buildings and all our stately homes were put up before there was a single planning or building regulation)

    In practice what we get is a bureaucratic, arbitrary and sometimes capricious process that rarely serves anyone. There are probably many answers to yourquestion of why they insist that you use London brick - the first thing that comes to mind is "because they can" A second one is that because it fulfills some notion of being 'in keeping' with your existing building.

    The good news is that most planners wouldn't know a London Brick if it bit them on the arse and they virtually never inspect a building to see if it was built to plan. (However if someone complains and they do, you could be in trouble) Generally speaking, planners are only interested in what it looks like but sometimes.........

    The history of planning in this country is of course complicated but much of it is based on stopping change happening, it is deeply conservative. They are having a hard time dealing with things like solar panels and appear to deeply dislike the use of modern materials in housing - not so much of a problem in offices, etc. (progress you see)

  5. Cavity wall insulation is really helpful in saving from heat in summers and it preserve heat in winters when we really need it. Overall Cavity wall insulation will also save your money and will provide you a best home.

  6. As much as a third of a homes heat is lost through its walls so having cavity wall insulation installed is definitely worthwhile. It can help reduce central heating bills and should in the medium and long term more than pay for itself.

  7. Interesting article. Here's another article on an alternative insulation method that you should check out:

    Invest in the Intelligence of a Passive House

  8. hi, interesting post...gret site
    good luck

  9. That is a hard decision!