Damp / Condensation Problem

[Redeye]

We moved into our new house 5 months ago. The building was built about 1780(ish) as a hay barn and was converted to a house around the 1920s.

We got a BDWPA specialist in to do a survey before we moved in who confirmed some slightly damp external walls which he attributed mostly to ground levels being higher on the outside than the inside and some concrete sills.

However, we now have what I'm fairly convinced is a condensation problem on the ground floor which is getting steadily worse. We have some big damp patches at the bottom of several internal and external walls, and I'm fairly convinced they're not rising damp because 1. they weren't there when we moved in, 2. they come and go 3. the bottom of the outside of the fridge is wet too. Higher up the walls is getting damp too and there are several patches on both internal and external walls. There's no serious damage yet, it's just a bit unsightly and needs sorting before we start decorating really.

I've installed an extractor fan in the kitchen which has made absolutely no appreciable difference (in fact it seems to have got worse since then). When I get back off honeymoon I plan to put an extractor fan in the bathroom too, which in hindsight I probably should have done earlier. I think I might also have to invest in a dehumidifier as a short-term measure to help dry the house out a bit as I'm not winning at the moment.

Has anyone got any other ideas or comments on my plans? I know the theory is that I need to ventilate and get rid of moisture from where it's produced, but in a house with 2 foot thick stone walls I haven't got too many options. I'm just worried that it's going to get worse when winter sets in, although it may turn out that having the central heating on helps a bit.

All suggestions welcome...

Thanks,
Dan

 

[biffvernon]

It might not get worse as winter sets in. In the summer the absolute humidity of the air, that is, the actual amount of water in the air, is often quite high, warm air holding more water than cold air. When it meets a cold surface such as a two foot thick stone wall or a fridge, condensation will form. The extractor fan doesn't help because it is just bringing more humid air from outside through all the cracks in the building and pushing that air out again after it has dumped its load of water on your wall and fridge.

In the winter the wall may be not so much colder than the incoming air and the air will actually be drier so there may not be a problem.

What it the wall plastered with? We had this problem when our wall was plastered with gypsum but when we changed it for lime the problem vanished. The lime is better at absorbing and water without damage and releasing it again.when the relative humidity drops.

The ultimate solution in a bad case is to insulate the inside of the stone wall with Thermafleece behind clayboard on timber studdwork.

 

[geoff]

I have thick stone walls and in summer often get condensation on the thickest part of the (exposed stone) wall next to the inglenook where it is a big mass about 6 ft thick. With the stove or heating on in winter there is rarely a problem. It depends on the moisture conditions (I am at the bottom of a valley just where two rivers join, which doesn't help matters for moisture) but it's just a slightly damp film to the touch on some of the stones (rather than water droplets) which can make it show a little darker. Unless it gets serious, you'll probably just have to live with it. I tried a dehumidifier, but it didn't make a lot of difference. Ventilation in summer and heat in winter are probably the the best you can do.

 

[Redeye]

Thanks - that helps explain some of what I'm seeing.

So it sounds like the extractor fan is best left on just while we're cooking to get rid of the steam. Likewise the best thing in the bathroom will be a fan triggered from the light switch with a run-on timer to get rid of the steam after using the shower.

As for what the walls are plastered with - I think its a combination of several things. The bottom meter or so on the ground floor seems to be different to the rest, but there's plastering and re-plastering all over the place which explains why there are cold spots at random places and why the condensation gets worse about half-way up the walls. I noticed that two walls either side of the fireplace in the living room are dry lined and consequently have no condensation.

It's a problem which will probably take months to solve, but it beats the hell out of being in a tiny newbuild so I'm not complaining. It's just a bit depressing when you get up each morning and see these great big damp patches in the kitchen We've got a whole load of other things to figure out when we get to changing the kitchen, but one thing at a time....

 

[worms]

the best thing in the bathroom will be a fan triggered from the light switch with a run-on timer to get rid of the steam after using the shower

If you have an electric shower you can have it triggered by the shower rather than the light so that you don't waken the whole household every time someone gets up in the night.

 

[NT]

Such things are generally condensation, though check for bad pointing on the wall or water runing onto it from rainwater goods. If condensation, reducing RH is the answer. Purchase + run costs for a dehumidifier are lower than for a fan, as it doesnt chuck your CH out, plus its al ot more effective. Just use a humidistatic one and dont set it aggressively, just enough to stop the condensation.

NT

 

[Redeye]

Thanks for all the help folks. Leaving the kitchen fan off except while we're cooking has reduced the condensation throughout the ground floor noticeably. The fact that we've had a few dryish warmish days has probably helped too, but I'd like to think that it's mostly not having the fan on all the time.

I think I'll probably experiment over the next few months to try and dry it out properly, perhaps with the help of a dehumidifier - probably a small price to pay in the grand scheme of things.

I guess the real answer to the problem is insulation related ie. trying to avoid the walls getting cold enough to cause condensation. I ended up having to dry-line a wall in the bathroom (because of very uneven plaster on a very uneven stone wall that I needed flat to be able to tile on) which had a noticeable effect in terms of insulation. Has anyone got any other suggestions to improve the insulating properties of the walls, particularly the external stone ones?

 

[Nemesis]

Try heating the place before doing anything - along with a bit of ventilation - see how it goes.

Gently gently!

 

[Penners]

the best thing in the bathroom will be a fan triggered from the light switch with a run-on timer to get rid of the steam after using the shower

If you have an electric shower you can have it triggered by the shower rather than the light so that you don't waken the whole household every time someone gets up in the night.

Actually, you can have it triggered by the atmospheric moisture content in the room.

 

[worms]

...at a price!

I'll admit, though that it is the best solution and the route to go down if you are buying and installing a new fan. You could even go one step further and have a heat recovery fan triggered by a RH detector switch.

 

[Lime]

Try heating the place before doing anything - along with a bit of ventilation - see how it goes.

Gently gently!

Continuous gentle heating is the only way to prevent condensation occuring at some time on thick stone walls.
Minimising the water content in the air will help but at some time the dew point will be reached when water condenses from the warmer air onto the colder stone.
The only way to reduce this possibility is to warm the stone or cool the air.

 

[Penners]

Continuous gentle heating is the only way to prevent condensation occuring at some time on thick stone walls

Gentle heating plus ventilation. No good saturating the warm air with moisture vapour unless you then get rid of that air.

 

[Lime]

Continuous gentle heating is the only way to prevent condensation occuring at some time on thick stone walls

Gentle heating plus ventilation. No good saturating the warm air with moisture vapour unless you then get rid of that air.

As Nemesis said and I quoted.

 

[Penners]

Sorry, Lime. I've only just got to chapter 2 in the How To Read book.