4. Cavity Wall Insulation

Cavity Walls

Your DIY Survey continues. First let’s find out what you really know.  Tick all that apply

◻︎   My cavity walls won’t have been insulated – I mean it’s pre-war and they didn’t do cavity walls then, did they?

◻︎   I never got round to getting the cavity walls insulated when the energy companies had been doing this for free. Not my best decision!

◻︎   It’s really complicated as the house has been added to over the years and I don’t know which bits are insulated and which aren’t.

◻︎   Because I am so efficient I was able to immediately lay my hands on the Vendor information pack from when I bought the house. Perhaps I should get out more.

◻︎   I think I’ve got the building survey somewhere which should tell me if I’ve got cavity walls. It will be in the attic where I’m going to look right now – I may be some time.


Cavity Walls

•Heads-up – you will need trade or professional advice on this.
•The outside walls are going to be the largest single component on every detached house. And it’s where you can really drive down the heating bills as well as improve comfort levels.
•Your DIY Survey starts with whether the outside walls are of solid brickwork or cavity construction (where you have an inner and outer leaf of brick or block with a cavity between). This tells you whether installing insulation within the cavity is an option.
•The ‘rule of thumb’ is that outside walls on 2-storey houses were built as cavity wall construction from the 1920s onwards. But in our area the local builders were ahead of the game and started to build outside walls as cavity walls much earlier (from the 1870’s) so there is an extremely high chance that your home is of cavity wall construction. (Though especially if the house is say pre-1920s you will need trade or professional advice on whether the cavity is suitable for insulation).
Fact. The legal requirement to install insulation in the cavity on new houses only came about much later, in the 1976 Building Regulations.


By the way, you can normally spot a cavity wall from the outside if all the bricks you can see are laid longways, with none laid shortways except at corners. (Ask a child to draw a brick wall and it will look like this with all the bricks laid longways!)

Why is this so important? It’s because there is a huge difference in the heat loss from these different types of constructions. To start with, although a post-war house built with uninsulated cavity walls is going to be around a third better than a mid-Victorian house with solid brick outside walls, it’s still way short of the Building Regulations standards even from the 1970s.

Outside walls built to current standards can be a whopping 8 times better at energy efficiency than a post-war house with no cavity insulation. So if your house is suitable, making a start on this by retrofitting cavity wall insulation, is absolutely worth doing, even more for detached houses.

Consult the NIA (National Insulation Association) is the trade body for wall insulation for a list of installers.