Condensation(?) on one wall in Victorian property

[YorkshireMidge]

A friend of ours lives in a top floor flat in a stone-built Victorian semi-detached house, and has what appears to be condensation problems on just one wall in a bedroom. Main points as follows:

The flats were converted about 20 years ago, and it looks to have been done well and to high standard as far as it's possible to tell from the finish.

The rest of flat seems fine.

The problems only occur during winter when it's very cold, suggesting this isn't penetrating damp from a leak. The pointing looks OK as far as it's possible to tell from ground level photos.

The problem seems to be at its worst below the window level, but some patches higher up.

The wall faces East so ought to get some sun. The mirror image flat in the other half of the semi is fine.

In spite of keeping the room well aired, and even using a dehumidifier, moisture can apparently form on the wall relatively quickly - say a couple of hours.

The previous occupants reckon not to have had any problems.

That wall has been painted since the previous occupants had it, which makes us wonder whether it had breathable emulsion on it before, so perhaps the problem WAS there but moisture didn't sit on the surface to the same degree.

We don't know yet what sort of plaster, insulation etc. would/should have been used.

The working assumption is the surface of the plaster inside is way colder than it should be for some reason on that particular wall such that the heating being on is making little difference to the surface temperature - such as a gap somewhere in the structure allowing cold air to get behind, or missing some insulation that is present elsewhere in the flat. Any thoughts/experiences/fixes appreciated. Thanks!

 

[jeds]

I'd say the wall is simply too cold for the moisture in the room, but the only way to know for sure is to measure the vapour levels and surface temperature across a range of timescales. You may well be right that the paint hasn't helped - it looks glossy? Ventilation may help but I reckon you are looking at internal insulation to really kill it off. What are you prepared to do to solve the issue?

 

[George_engineer]

Cold air from the roof getting behind the plasterboard is a real possibility. They're hard enough to seal in a conventional room and this is up in the roof.

It's probably all covered up but, if you were prepared to make good afterwards, you could make some trial holes around the perimeter and where the damp is appearing. If you can feel a breeze then external air is getting in and chilling the plasterboard. You would then need to go round and seal up the joints. Alternatively, remove and replace with insulated plasterboard - more expensive materials but you'll be plastering either way and you get a better end result. With the insulated board, ensure continuous beading aroudn the edges to prevent drafts.

 

[YorkshireMidge]

I'd say the wall is simply too cold for the moisture in the room, but the only way to know for sure is to measure the vapour levels and surface temperature across a range of timescales. You may well be right that the paint hasn't helped - it looks glossy? Ventilation may help but I reckon you are looking at internal insulation to really kill it off. What are you prepared to do to solve the issue?

Thanks. The paint is an eggshell finish, and it just looks more glossy due to the moisture. I've advised my friend to have a dig about and see if he can find any of the paint used, as the eggshell might still be impermeable and making the situation worse. If a dehumidifier isn't even helping that much, then it does suggest an underlying problem that is going to have to be solved as it's too bad to live with apparently. My friend does have the option of calling the management company in for a proper look around the outside - so that might be worth doing before ripping things out inside.

Cold air from the roof getting behind the plasterboard is a real possibility. They're hard enough to seal in a conventional room and this is up in the roof.

It's probably all covered up but, if you were prepared to make good afterwards, you could make some trial holes around the perimeter and where the damp is appearing. If you can feel a breeze then external air is getting in and chilling the plasterboard. You would then need to go round and seal up the joints. Alternatively, remove and replace with insulated plasterboard - more expensive materials but you'll be plastering either way and you get a better end result. With the insulated board, ensure continuous beading aroudn the edges to prevent drafts.

Thanks for the ideas. I think the holes might be the way to go as the first step esp. if my friend can find any of the paint as it could be tidied up afterwards whilst the best approach is considered. I was mulling over that there must be something left of the loft too, but I can't recall seeing any access.

 

[YorkshireMidge]

Just some follow up questions.

Would I be right in assuming that this building would likely be stone on the outside, and a brick (or rubble) backing, and no cavity?

I got my first proper look at the problem this morning and it soon became clear that the affected walls aren't plasterboard - it is plaster onto solid wall. This is a surprise as I would have expected that anyone doing a complete refurbishment/modernisation as recently as 20 years ago would have taken steps to insulate + it is clearly plasterboard on outside walls of some other areas of the flat such as lounge and main bathroom, and explains why they don't have a problem.

The outside temp at the time was 4.3 degrees and the plaster surface temp on the inside was just 5.5 degrees in the worst affected areas of the wall, and around 8-9 degrees in the rest. That says to me there is simply no insulation.

Human factors such as the relative humidity and general level of heating are clearly contributory factors too when we measured them, but they can be dealt with. e.g. it transpired that the dehumidifier being used was one of those little electronic ones and nowhere near up to the job of keeping an old property like this dry - so that is going to be replaced. I imagine that step alone will improve the situation significantly.

But the feeling is we need to do something with the affected walls. I've found a product called Wallrock KV600 which seems to get either rave reviews, or comments like it's thick wallpaper and can't possibly be that good. But compared with having to add insulating board, re-do the skirting etc. etc. Wallrock does look tempting as a relatively quick and easy compromise. What's the thinking?

On the subject of insulating board solutions, if we were to take that approach instead, how thin could we get away with? I've come across Celotex before - but only in the context of shoving it in cavities and it's usually pretty deep in that application.

Thanks!

 

[fourtytwo]

I used to live in an old Victorian house where part of the kitchen had been outhouses with quite a severe condensation problem on there outside walls. We found a product like wallpaper but made of polystyrene about 1/8" thick, applied that to the walls and then wallpapered over, completely successful (in that case) so you never know how thin you might be able to get away with!

 

[YorkshireMidge]

I used to live in an old Victorian house where part of the kitchen had been outhouses with quite a severe condensation problem on there outside walls. We found a product like wallpaper but made of polystyrene about 1/8" thick, applied that to the walls and then wallpapered over, completely successful (in that case) so you never know how thin you might be able to get away with!

Thanks. The Wallrock stuff is about 4mm so comparable to that.

 

[JohnD]

Considering that cavity wall insulation is about two inches thick, a quarter inch is pretty trivial.

 

[George_engineer]

You can't insulate wet walls - damp need fixing first. The wallpaper is unlikely to help as it's so thin and would just be hiding the underlying problem. Wet walls are cold walls.

if it's solid plaster I'm inclined to think there could be a roof leak and tracking around. It may be that a small roof fault is chilling a wall, leading to further condensation.

In the outside picture the gutter has grass growing in it.

 

[Koolpc]

Condensation.

Warm the room. Ventilate. Insulate that wall.

Wallrock is a good idea

 

[YorkshireMidge]

Considering that cavity wall insulation is about two inches thick, a quarter inch is pretty trivial.

Agreed. In an ideal world, that sort of thickness of insulated plasterboard would have been added when it was refurbished. But now, there's fully fitted wardrobes on the adjacent wall and issues like that which would make it more difficult and expensive to do. If it was my property and I was expecting to live in it umpteen years, I'd probably bite the bullet and do it, even if it meant ripping out the wardrobes and stuff. But it's their first home so the arguments for and against are more nuanced.

You can't insulate wet walls - damp need fixing first. The wallpaper is unlikely to help as it's so thin and would just be hiding the underlying problem. Wet walls are cold walls.

if it's solid plaster I'm inclined to think there could be a roof leak and tracking around. It may be that a small roof fault is chilling a wall, leading to further condensation.

In the outside picture the gutter has grass growing in it.

Human factors need dealing with first - RH in that room was 80%+ and the heating was far too low. Once that's dealt with, we should be able to tell if there is any residual issue of the type you describe. My gut feeling is there isn't. If you wipe the walls, its unquestionably condensation forming very quickly. Yeah, I saw the clump of grass too and the gutters were apparently done last year so could certainly do with another clear out as there are a lot of big old trees in the area.

Condensation.

Warm the room. Ventilate. Insulate that wall.

Wallrock is a good idea

Looking that way - it's just a case whether Wallrock is adequate as its unquestionably a compromise.

 

[jeds]

Whether surface condensation appears or not can be a very fine balance. A simple wall covering might make the difference - you won't know until you try it. I don't have experience of Wallrock KV600 but there is another material called Sempatap, which is often used in social housing, and I do know that can be partially successful. To be honest, I don't really like either of these materials (both really fall under the general heading of 'a bit of a bodge') but if they solve your problem, some of the time, without too much fuss and cost, then it might be worth trying.

Just to note that neither material will make any real difference to heat loss - both work simply by raising surface temperature sufficient to reduce condensation on the surface.

 

[YorkshireMidge]

Whether surface condensation appears or not can be a very fine balance. A simple wall covering might make the difference - you won't know until you try it. I don't have experience of Wallrock KV600 but there is another material called Sempatap, which is often used in social housing, and I do know that can be partially successful. To be honest, I don't really like either of these materials (both really fall under the general heading of 'a bit of a bodge') but if they solve your problem, some of the time, without too much fuss and cost, then it might be worth trying.

Just to note that neither material will make any real difference to heat loss - both work simply by raising surface temperature sufficient to reduce condensation on the surface.

I think I'm firmly on the same page. A lot hinges on how long they intend to stay there really.