How Do I Know If I Have Cavity Walls, Or If They Have Been Filled?


3 Answers

Julii Brainard Profile
Julii Brainard answered
Assuming you're in a house with brick external walls: If the bricks are all lying length wise (so no short sides showing) this is a clear sign of cavity walls.  Houses that are built from solid brick (double layers of brick) will have walls showing a few long sides of the bricks, then a short side, then a few long sides, etc.  See this page for examples:

Checking whether the cavities have been filled is harder.  If you have windows replaced you will be able to view into the cavity to see for yourself.  The filling is usually a yellowy material that will be noticeably different from the solid brick or concrete either side.  You can also try to peer down the cavity from your loft, this may involve crawling out over ceiling joists and trying to angle a mirror and torch so that you can see under the eaves and down the cavity.  If you ever need to drill through the walls, a small amount of material may spill out or appear as residue on the drill bit.  Building work that knocks through outside walls may also let you see one way or another.

But the easiest thing to do is usually to get a survey done (no obligation) by a reputable insulation company.  The professionals drill a small hole into the outside wall, and use something called a boroscope to peek into the wall.  The boroscope is like a tiny periscope with a bright light on it.  You can look through the boroscope for yourself and verify whether there is any insulation in there.
Anonymous Profile
Anonymous answered
To check for cavity wall insulation that has been added after construction look for small 1 inch wide holes. These will have been filled in with some concrete and will be dotted around the outside of the house. (normally located between the bricks in the mortar).

We had our house done recently and they had to drill holes every metre or so, so that the cavity could be filled up.
Mark Smith Profile
Mark Smith answered
If you're looking for someone to do the survey in your area, you could try the following website. If you don't have cavity wall insulation or loft insulation and you're on a qualifying benefit, then you may well be able to get insulation installed free. Even those not on benefits are eligible for grants in most cases.

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