Cellar advice

[dandrew]

If this topic has been discussed ad naseum before, I apologise, but if so perhaps someone could point me to the correct thread in the archives.

We are the new owners of an 1860 stone built house with cellars, whose features we are in the process of re-instating. We would like to use the cellars as habitable space, but unsurprisingly they are damp, being below ground. Moisture seems to be coming up through the floor, which looks like Yorkstone, because it is damp. This causes a green mould-like coating to grow on anything organic - wood, papers etc and the smell is starting to permeate the rooms that are above the cellars. A previous survey (not ours) advised the then owners to 'remove the under-drawing in order to improve air circulation'. Presumably under-drawing was lath and plaster that covered the joists, since the joists are now completely exposed.

So in order to a) dry out the cellar and b) abolish the smell it will be necessary to waterproof the cellar. Given that most (all ?) of the damp seems to emanate from the floor will it be necessary to pour a new concrete floor on top of a plastic damp-proof membrane? If so we would probably have to dig down to establish sufficient head-height to pass building regulations. Would it then be sufficient to dry line the walls with a waterproof membrane or would tanking ( ) be needed ? Clearly if we prevent moisture from coming up through the floor it will have to go somewhere else, but where ?

Any information gratefully received.
Thanks, David

 

[NT]

Does a new floor require BR? If you dig down further you're reducing and possibly undermining your foundations, both of which are a Bad Idea, one of which is a Suicidal Idea.

Presumably you would relay the yorkstone on top.

The water doesnt 'go' anywhere, the ground is always wet.


NT

 

[Moo]

"So in order to a) dry out the cellar and b) abolish the smell it will be necessary to waterproof the cellar"

Stone paving gets wet when it rains, and dries when it gets warm, because the water evaporates.

So, if your cellar is kept warm enough the moisture will evaporate and your only problem then is to provide somewhere for the moist air to go.

If improved ventilation doesn't do the trick, it may have to be backed up by some sort of dehumidifier.

Our cellar has a radiator for the winter months, and the door at the top of the stairs is only shut when small children visit the house. No problem with damp, even though we hang our washing out to dry there.

 

[dandrew]

I can understand that warm temperatures should dry out something that is wet, but despite 3 solid weeks of +30°C outside temperatures the cellar floor is as damp now as it always has been. But isn't the point of cellars to keep things cool - we still have the original cold slab that was used as an early refrigerator

Unfortunately there is limited opportunity for ventilation. We have 2 small children, so the cellarhead door has to be locked all of the time. The dehumidifier might be worth a trial run, just to see how much water we can extract from the air

 

[Moo]

Would it be possible to fix something like a stairgate at the top of the stairs?

and - have you checked whether there's something like a spring, or a leaking drain or water pipe running under the house? I seem to recollect a thread not that long ago about just such a problem.....

I'm only making suggestions/observations based on no technical knowledge at all, but I know there are people around who can give some expert advice. What with the time of year and the debilitating heat and humidity they may well be otherwise occupied at the moment (ie, on holiday or comatose) so please be patient.

 

[Lynn]

I can understand that warm temperatures should dry out something that is wet, but despite 3 solid weeks of +30°C outside temperatures the cellar floor is as damp now as it always has been. But isn't the point of cellars to keep things cool - we still have the original cold slab that was used as an early refrigerator

Unfortunately there is limited opportunity for ventilation. We have 2 small children, so the cellarhead door has to be locked all of the time. The dehumidifier might be worth a trial run, just to see how much water we can extract from the air

If you go the dehumidifier route, which is made difficult by lower temps in that kind of cellar, I would recommend one like this:

http://www.thermastor.com/prod_santafeadvance.htm

We put this unit in our (sometimes leaky) basement and it is extremely efficient and effective. I'm not sure what kind is available in the UK, but I wouldn't waste money and energy on a typical de-humidifier. This company also has a discussion board that might help in finding the right unit for your difficult situation.

 

[mark_j_k]

Apert from one corner of the cellar that always is damp (drain fault) the floor is usually dry. But this time of year there is alot of moisture on it and alot more salt on the walls too. Even in winter time the floor is relativly dry but the air is more damp.
I think we have enough ventalation down there - 2 old windows bricked up with bricks of their sides so the holes are showing and a few above ground floor vents.

 

[Moo]

Ahah!
So - the floor is mostly dry, apart from where there's a drain fault? Solution - fix the drain.

In winter the floor is relatively dry but the air is more damp (than in the summer, presumably). Which makes it seem that the cellar is behaving just as it was designed to do.

So where's the need for all that expensive digging and concrete and plastic? Instead of the moisture quietly and harmlessly evaporating, it would sit under the dpm, look for a way out, and make straight for your walls. Which would then get wringing wet (as would structural timbers).

I reckon that if you were to:

a) get a stairgate
b) fix the drain, and
c) check the website that Lynn has posted

you would have a much healthier bank balance (and a much healthier house, to boot).

 

[mark_j_k]

I forgot to mention in my last post, I was talking about my house! not dandrew's

Sorry for any confusion.

 

[NT]

> Instead of the moisture quietly and harmlessly evaporating, it would sit under the dpm, look for a way out, and make straight for your walls. Which would then get wringing wet (as would structural timbers).

This might or might not occur at ground level, but not below ground. The earth on the outside of the walls will always be wet regardless of whether the floor evaporates or not. An underground floor will at best evaporate a tiny percentage of the water in the earth. In a cellar a dpm in the floor wont affect the walls.


A stairgate would help cool the house in summer - and in winter tooif the stair door were left open.


NT

 

[Lynn]

. This causes a green mould-like coating to grow on anything organic - wood, papers etc and the smell is starting to permeate the rooms that are above the cellars.

This talk about opening this area up with a stairgate concerns me since the above quote indicates mold. That is not healthy to live with and I wouldn't invite it into my living space.

 

[Matt Green]

The mould is only there because the conditions in the cellar create an environment where it will grow. Reducing the humidity will limit the mould growth, although the existing growth is likely to need to be cleaned off.

Is there really no way of ventilating the cellar to an external point? A humidity-sensitive extraction fan is a much better long term solution than a dehumidifier. Dehumidifiers in cellars will constantly pull water through the walls spoiling any finishes and possibly the internal face of the masonry. Not the best in long-term solutions.

Matt Green

 

[Moo]

There - I told you so. This site is simply bristling with real experts.

But I still stand firm about the stairgate. Our cellar lets cool air into the house in the summer (much-welcomed at the moment) and is kept at the same temperature as the rest of the house in the winter by the radiator. It only smelled musty once - when we had a house-guest with an arthritic dog and had to keep the door shut for several days.

 

[Lynn]

From the Thermastor forum, here is the accepted practice in the US. I'm not sure what your RH conditions run in UK...

There are two sources of moisture in the crawlspace. The earth floor is giant year around moisture load. The vented air outside is a moisture source during the summer or when the outdoor dew points are +50^ F outside. Vents open during the winter when outside air is dry, removes the moisture evaporating from the uncovered earth.
Cover the earth with plastic and close the outside vents year around. Keep the space <60%RH (50%RH, ideal) with dehumidification.

This would directly contradict the idea of opening up the cellar in summer. Now maybe you don't have such high dew points, but the quote provides some numbers to judge. As far as the next idea posted:

Dehumidifiers in cellars will constantly pull water through the walls spoiling any finishes and possibly the internal face of the masonry.

I don't have any experience with spalling due to the use of a dehumidifier. Usually that is due to water pressure built up behind walls from excess ground water. The catch-22 is that if you want it dry then no matter how you do it there will be a small gradient created to "pull" moisture in. The point is keeping up with the load so that your environment is not moldy.

 

[Matt Green]

The point is keeping up with the load so that your environment is not moldy.

Hence the suggestion to use a humidity-sensitive fan that would engage only when humidity reaches a certain theshold.

The mould isn't the issue here, in the cellar no one is likely to be inhaling the sort of spore loadings that would lead to a immuno-suppressant response in the inhabitants. Geting teh environment within the cellar to point it can be used as reliable storage will solve the mould problem by proxy.

If there it a significant amount of water beneath the floor it will be behind the walls as well, given the entire structure is subterrainean. There might be some variation with respect to the local water table, but the point stands. Ground water brings with it salts dissolved within it that crystalise on he interior surface during the evaporation process. I don't know how much of a problem that is in the US, here a salt effloressence can certainly damage softer masonry surfaces.

Incidently, covering the earth of a sub-floor void would increase evaporation through the walls. Not ideal in period properties, unless the void in question in very deep and the finish on the walls isn't important.

The root of the problem is that the cellar was never designed for the purpose now intended. Short of lining or tanking it, it may never be.

Matt Green

 

[NT]

Matt Green

> A humidity-sensitive extraction fan is a much better long term solution than a dehumidifier. Dehumidifiers in cellars will constantly pull water through the walls spoiling any finishes and possibly the internal face of the masonry. Not the best in long-term solutions.

Ah, I'll differ on that. First a fan throws heat outside, a dehumidifier doesnt, and this tips the financial and ecological balance in favour of the dehumidifier.

Second the rate of water transport through the walls depends on interior RH, and a dehumidifier can reliably and controlledly be set to whatever RH you choose. A damp operated fan can not. Thus the dh does no more salt damage than the fan. Both will cause salt deposits, and there are ways to deal with this. One is to lime the walls, the lime acts as a sacrificial layer.

Always pick a humidistatic dehumidifier.


NT

 

[NT]

From the Thermastor forum, here is the accepted practice in the US. I'm not sure what your RH conditions run in UK...

There are two sources of moisture in the crawlspace. The earth floor is giant year around moisture load. The vented air outside is a moisture source during the summer or when the outdoor dew points are +50^ F outside. Vents open during the winter when outside air is dry, removes the moisture evaporating from the uncovered earth.
Cover the earth with plastic and close the outside vents year around. Keep the space <60%RH (50%RH, ideal) with dehumidification.

I've never heard of this done in the UK. Certainly it would work, but here we always obtain healthy RH in floor voids by passive means. RH gets fairly high down there, but if its all working ok not high enough for the wood to rot.


NT

 

[NT]

Hence the suggestion to use a humidity-sensitive fan that would engage only when humidity reaches a certain theshold.

That will actually bring damp into the cellar some of the time. When the cellar is cool and outdoors is hot and a little damp, the fan will run and warm air with more water vapour will be brought in.


NT

 

[Matt Green]

First a fan throws heat outside, a dehumidifier doesnt, and this tips the financial and ecological balance in favour of the dehumidifier.

I certainly can't argue with that.

Second the rate of water transport through the walls depends on interior RH, and a dehumidifier can reliably and controlledly be set to whatever RH you choose. A damp operated fan can not. Thus the dh does no more salt damage than the fan. Both will cause salt deposits, and there are ways to deal with this. One is to lime the walls, the lime acts as a sacrificial layer.

Always pick a humidistatic dehumidifier.

That is also sensible, although are humidistatic fans that much more unreliable than humidistatic dehumidifiers? I would have thought the components were reasonably similar. At this point though we have reached the ragged edge of my knowledge.

I am, I suppose, erring on the side of caution having seen heavy-handed contractors install DHs that suck the sweat from your body in cellars in an effort to dry them, then call us in to comment on their ineptitude. There is less scope for damage with fans, don't require you to regularly lift litres of water from your cellar, and don't become a feature of the room. However, that all said, I see different situations than regular domestic environments and it seems there may reasonable arguments for routine DH use.

I like the sacrificial lime idea.

That will actually bring damp into the cellar some of the time. When the cellar is cool and outdoors is hot and a little damp, the fan will run and warm air with more water vapour will be brought in.

That assumes you bring the air in directly from outside and not through the building. I'm not sure if that would generate a big effect or not.

All good stuff, this.


Matt Green

 

[biffvernon]

All this fanning and dehumidifying is promoting the consumption of even more electricity. Surely, a more sustainable solution would be to use the cellar for growing mushrooms, ageing wine, indoor swimmimg pools etc..