Hoping someone might have even a faint understanding of this and can help or point me in the right direction.

Got a 3 foot crawl space under the ground floor of my house – between the ground and the floorboards. The ground is just that – dirt.

I've dried it out using a fan and a dehumidifier and now I can see where the problem areas are. It seems the walls in certain parts are letting damp in which is making the rest of the ground in these areas damp and is spreading over time to make a large proportion of the underhouse bit damp.

I think it is partly to do with the earth on the other side of the wall (as the ground floor is strangely enough at ground level so the crawl space is all under ground) transmitting the damp through the wall. I think it is also to do with the water table being about 3 inches below the surface of the crawl space as I can dig down and it gets really wet – checked the pipes etc and not to do with cracked pipes and I've checked during yesterdays seriously heavy rain and no leaks visible.

Anyone got any ideas what i can do as I don't want to leave a dehumidifier running all year round.

I can provide fotos if that helps.

Cheers in advance

Dampwacked!

Is it not just, as you say, the water table? It sounds on the face of it to be simply that, especially if you cannot find any leaks.

Remember though that a leak may be coming from elsewhere and migrating. We recently had an extension built and found that some pipes outside the boundary of the house were leaking and damp was passing under the house.

I would also think that artificially drying the underneath of your house could cause other problems due to shrinkage!

More info needed…
How old is the house? How are the walls constructed? Is there a damp proof course? Also have the ground levels outside the house beenraised at any time? (they tend to get raised over time)

All suspended ground floors need ventilation, ie, vented through out… at 1800mm intervals so outside air flow can be achieved, that includes internal walls.

Also check for rainwater drainage and make sure run off doesn't head towards the house, if it still causes excess dampness then a french drain system around the property should help.

HTH

Its been damp since it flooded a few years back and the smell got to a point where we had to do something about it.

The house is an 1850's terrace house with brick construction. Damp proof course in place. Ground levels are still below the damp proof course, although the crawl space is below the damp course. We're trying to get the smell away from the house as it is really unplesant and when it is dry there is no smell.

Next door's crawl space is tanked so they don't have the same problem.

Checked drains – there was a crack in one but fixed that – run off is in the right direction- away from the house.

The air bricks in the house are spaced nicely (about 1200mm apart but on the other side the joist from the floor means there is only about 1inch between the air brick and the joist for air flow – is this normal?? You can still see the wind blowing the cobwebs around.

There may be limited air flow, just because the cobwebs are blowing it may not means air is being drawn in at a sufficient rate to dry the floor after flooding, even as long as a few years back, the last three years haven't been particularly dry ones so speed of drying out maybe reduced.

Damp rises and will find it's way to the point of least resistance, so through capillary action will head through drier ground, ie under the house.

Damp soil would not normally give off such a smell if it ventilated well and i believe without seeing it this is the fault here.

A french drain could help in not retaining moisture against the walls and this would aid in the ground under the house drying out too.

Sharki – interesting. French drain – is that like a french letter only on a more industrial scale???

Can I put one inside the house on the inside of the wall or just the outside? The outside of the wall has paving up to it so acces isn't easy.

Ventilation I think might be an issue here as the rooms are carpetted and also have laminate flooring down. Thinking the floor might not be breathing as much as it needs. Thinking about putting a vent in the floor in the rooms to help air flow especially in the laminate floored areas but not sure if this is a good idea.

I've heard of products you can paint on the walls which stops rising damp (Like this… http://www.aquasealeurope.co.uk/block.asp ) but not sure if it is suitable, will do more harm than good and will actually work…

Cheers for the responses so far all been very useful.

I should mention you can see a tide mark on the bottom third of the floor on these walls where it is damp below this line.

Happy to chuck up some photos if it helps anyone.

Tide mark….do you mean a distinctive line of damp above the finished floor level?

This would be rising damp and needs to be treated with either damp proof injection or a new damp proof course, BTW outside ground floor levels needs to be at least 150mm below damp course.

Carpeting over and laminating shouldn't affect ventilation if external air bricks are installed at each joist end and gaps in suspending walls, the void only needs ventilation and this will aerate the floor board too, fitting an internal floor vent may help but will let smells into the rooms, which will need to be ventillated too. (Modern U value regulation is lessening this so new windows and external doors will lessen good ventillation of older damper houses)

A french drain is basically and trench along side a wall, which has a perforated pipe in the bottom leading away from the house(to usually an soakaway) the trench is then filled with loose clean chipping, this can then be paved over, or covered in soil(on top of porous membrane) sometimes the wall is cleaned and tanked down to foundation level.
This is not so affective internally IMHO.

If the water table is quite high the ground will always be damp, and other than a full internal tanking job(£££££££'s) you'll not prevent it..

I'd really advice you had someone look at it all, call sovereign for good advice and evaluation.

poss not entirely related.

Anyway, parents bungalow – damp on inside walls at bottom, investigation revealed that the previous owner used plastic as weed proofer under the gravel that surrounds the house, this was funnelling water off the side of the plastic – or against the house wall, me and dad cut the pastic back and dug a 18" trench round the area and hardcore filled and topped with gravel, a lot better.

Also fixed a similar issue on gfs semidet outside washhouse, damp on inner wall, issue is gutter draining straight into ground outside (on neighbours side), I've dug a huge soakaway (encouraging water away from wall and hardccored) and again noticeable improvements.

Sharki – posted 4 pics here as easier to explain with a photo than in words

http://www.flickr.com/photos/bushwacked/3885116204/in/set-72157622229207558/

Tide mark is more a damp mark than anything else, as you can see from the photos the ground has dried out (Light grey colour) but where it is getting damp it is getting darker again.

Why sovereign and they're not the hard sell kinda people are they? Do I get in touch with their contractors or sovereign direct???

Do you have ventilation gaps in the dwarf walls between the rooms in the crawl space ?

Yeah, you can crawl from room to room and there are bricks out in the interior walls also. You go down one hole in the centre of the house and can get to all parts of the house.