Waterproof insulation in old damp house

[NotQuiteUsual]

Yesterday the contractors for the council who are doing the EC04 Scheme came round to inquire about doing insulation and smart home heating through it. I'm all for getting the house to stay warmer, but I know cavity wall insulation isn't always the answer. The house definitely has some areas of damp, it's a Victorian terrace and needs to breathe. We manage the damp by being militant about ventilation and keeping the place warm(as we can this year) and clean through the cold wet months.

Now they're saying this insulation material is waterproof so it stops any rain or humidity in the air from coming through the wall. But it's the internal damp not being able to escape I'm concerned about. Is it something I even need to think about it am I just making problems where there are none? I'd love to insulate the house. But if we need the windows open all winter because of moisture it's pointless! Any one with experience I'd love to hear your thoughts!

Are you sure you have cavity walls, if it is Victorian? I'd be very careful, I can't imagine sticking waterproofing in the wall itself is going to help, won't it just make the wall a sweaty mess? We deal with damp in old houses by using sorting the source of anything penetrating, using breathable paint, warming and ventilating, like you say.. All walls of any age will have some moisture in them, we have unrealistic expectations nowadays expecting everything to be dry as a bone rather than working to manage it.

I’ve heard enough horror stories about it that I would walk away.

I would try to sort out the existing damp as a priority, it has a cause and a cure hopefully. I live in a Victorian house and treat damp as a serious concern especially with condensation in bathrooms.

My DPs got heating installed through one of these schemes years ago - the pipes ran down the walls in the rooms to the radiators, boiler kept going out due to ?position of oil tank (windy exposed spot). They will probably be the company that gave the council the cheapest quote, so not the best by any means.

I live in a single brick Victorian workers cottage in a pretty rainy area. The brick is very old and spongy and we have rendered external walls (I suspect not lime render). We’ve never suffered with damp - I think because there are at least two air bricks in every room in the house, and an efficient electric ventilation fan in the bathroom. We also crack the upstairs windows and leave them like that from May to October.

But, the house isn’t particularly warm, and I’m also worried about insulation. We’ve added extra insulation to the loft, have a decent roof, and will be replacing all windows and external doors at some point as the ones that came with the house are well past their best.

I really didn't think it would have a cavity, but they did a check and surprisingly it does. I'm glad I'm not the only one thinking it could be a disaster! I asked the guys, but they were too dismissive for my liking.

What I might do is wait for the others in the first round on the street get it and see how it goes for them.

Did they actually say ‘You need cavity wall insulation’?
I don’t see the downside if you have a cavity.
If you already have damp, you shouldn’t, so investigate and resolve that first. Where is the damp? Any pictures?

No they didn't say we need it. Just that it's free through the scheme and we qualify for the first round. I asked about the damp and whether it was the right choice for these houses which is what they dismissed as they're using waterproof insulation, not the wool based stuff. I'll try get some pictures of the two damp spots tonight.

Basically both are on joining walls to the empty house next door. One is a small spot above the skirting board which isn't damp to touch, it's warm and dry feeling and looks like the salts coming out. The other is by the front door so I assume the seal is gone, again not visibly damp but the gloss paint has pealed away and the plaster is slightly textured like it could be salts, but just as likely to be a bad job. The plastering is very poorly done in that part of the house.

www.heritage-house.org/damp-and-condensation/insulation-related-damp-problems/cavity-wall-insulation-1/cavity-wall-insulation.html

cavity wall insulation not recommended for old properties.

An interesting post by bilbodog. I've not seen other comments about cavity wall insulation getting wet but the points made seem sensible in the heritage post given. I wonder if anyone else has experience of this?

It is interesting. The link @bilbodog gave is mostly complaining about poor preparation or execution. We can forget about blown fiber as it’s only the coated polystyrene balls nowadays. However if the surveyors don’t open up the cavities enough to do an in-depth assessment, then yes mistakes can be made.
For a mid terrace house, it’s reasonable not to cavity fill as the bulk of the walls are adjoining the neighbours so are already ‘warm’. Maybe if there is a reliable prevailing weather conditions you could do the opposite side.
However for a detached house I’d be giving it serious consideration.

Don’t do it. It will cause more problems than it solves. And the explanation makes no sense at all- much of the moisture in our homes comes from us- breathing, cooking, drying clothes, showers etc- what they seem to be suggesting wouldn’t allow all of that out. If you’re wanting to save on your heating bill I’d suggest better loft insulation, and sorting any obvious drafts, like windows and doors (curtains and window insulation around the edges). I also agree that I would try to get the damp
sorted as well.