Cavity wall insulation

[SilenzioBruno]

Was a bit surprised, while having kitchen windows replaced in our 1900s terrace, to find out that there were cavity walls with a 4" gap between. This makes it seem like it would actually be sensible to investigate installing cavity wall insulation.

But, I've heard plenty of horror stories about adding the insulation and then having lots of issues with damp. I'm also struggling to understand what would prevent the insulation from falling down between the air bricks and blocking them up. Maybe that's because I don't understand the construction properly. Maybe the damp proof course would 'catch' and hold up the insulation?

Anyone have any experience of successfully installing cavity wall insulation in a property like this? Any tips or pitfalls to watch out for?

Our property is not that old, but we had concerns about moisture transfer with foam insulation, and about loose insulation falling through, under certain situations. We went for blown glass fibre, and so far have had no issues.

As for the air bricks, they do not normally open into the cavity, but form a tunnel directly to the interior of the house.

Thanks Dilbertian, that’s a really helpful diagram. :) How did you go about finding a firm to do it? Any tips?

Start by looking at your local council website, and your energy suppliers. Sometimes they have a discounted or subsidised contract. It will be with a reputable company that is unlikely to go bust or run off with your money.

Installers can be forced to remove insulation at their own expense if they recklessly put it in an unsuitable wall (bad brickwork or pointing, loose render, leaking gutters causing damp, some exposed locations, rubble in cavity) so they are quite cautious now in checking for defects and may refuse orders until faulty walls are repaired.

You will not see many letters or articles from the millions of satisfied customers who save energy and have no problems, because they are not newsworthy.

That’s a good point about newsworthiness pigletjohn, thanks. I’ve not renovated a house before and since it’s perfectly liveable now the worst windows are replaced, I want to go slowly to avoid stupid mistakes!

Another thing I’m curious about is the bathroom at the end of the kitchen. I think it is single skin. It’s certainly solid wall without a cavity because the walls are visibly much thinner. I wonder what the effect will be on the already cold and damp-prone bathroom if we insulate the adjoining kitchen. Would it be sensible to investigate insulating cladding for the external bathroom walls at the same time?

You are fitting an effective extractor fan, aren't you?

Yes, that’s on my list this weekend, for the bathroom at least.

Kitchen currently has one of those shiny hoods that just ‘filters’ and pushes the air out at the top. I want to get an extractor that vents externally when the kitchen is done in a few months.

There is a 'Green Book' for our area. It's like a regional Checkatrade, except that small businesses and tradesmen are proposed by their customers. Entries cannot propose themselves, nor take out advertising in it.

We get most of our workmen from the Green Book. And when we employ someone who's been recommended to us by a friend, it generally turns out that they have an entry in it. We've been pleased with all the workmen we've employed this way.

Thanks Dilbertian. That sounds like a good system.