Rising damp / hole in the ground

[Zebra]

I have a corner of the house which is very wet, and I would like any opinions on what is the cause. I removed the cement render inside and out in the Spring, it dried out a bit. Now it seems to be getting wetter and wetter, worse than any other part of the house, and especially at the bottom.



I've ruled out penetrating rainfall, as I've covered it from the outside and it's still getting wet. The floor is cement, but it is elsewhere, and I don't have this damp problem elsewhere.

There is a big hole in the ground, just adjacent to this corner of the house. I don't know how long it has been there, it is about 1.5m deep and 1m sq in area. It is cement lined. The gutters all used to drain into it.




The two pipes in it - one is the runoff from my French drain, and the other is now redundant. It never used to overflow, so it must just leak into the ground when it reaches a certain level. I have not let the water reach a level higher than the inlet from the French drain all summer, as that would flood the French drain. In due course I will dig a soakaway either to connect directly onto this pipe, or to empty the hole before it floods the French drain. For now I run out with a bucket when it rains.

The rising damp is going as far as the top of the brick wall, and affecting the timber frame which sits on top. It perhaps always did, as this corner of the frame was rotten when I uncovered it, and I have had to repair it. I attributed that at the time to the cracked cement render, but perhaps it was coming up from the ground.

But does the wall have some sort of vacuum system? A network of drinking straws? How is so much dampness coming up when the water level is so much lower? There does not seem to be a high water table here. I've dug down in other places and the ground is dry to at least as deep as the foundations of the house, which go 4 courses below what you can see in the picture above.

What do you think I should do? Fill in the hole? There are advantages in filling it in, because it will get in the way of the foundations of the new building which has to go in place of the side extension (the wall in the right side of the frame in the picture above). But then again, it's part of the house's history, I don't know who put it there and why. Perhaps to harvest rainwater. Very grateful for use of your grey matter on this one...

 

[middi]

If there is no dpc in the wall those red bricks will suck up water like a sponge. If the subsoil is well drained there is less of a problem than a subsoil is that easily saturated.

It is a question of investigation to see what is the problem is the vicinity of that wall. The possibilities could be quite a few and very difficult to advise on remedy until the cause of the problem as been identified. I certainly would not want to fill that hole, I would want to know if it is working correctly regarding what is supposed to flow in it, if it is sound and if it is flowing away correctly.

Middi

 

[Zebra]

There is definately no DPC. If I need to investigate further, where should I focus my investigations? Where should I look and what should I look for?

How about emptying the hole and polythene lining it, just to see if that makes a difference? Or, I could empty it and temporarily put something in it, like a bin or barrel, to catch the rainwater, which I could then bucket away. Then I could see if the water in the wall is coming from the hole. Might try that.

 

[robgil]

You say your French drain drains into the hole?
If this is correct then that is your problem right there, surely?
Isnt the point of a french drain to carry water away from the building and not to dump it right below a wall?

If it were me , and all the other pipes were redundant and only the french drain drained into the hole I would extend the french drain to go somewhere else then try to figure out if filling the hole in would be a good idea or not.
In the mean time I would put a fan on the damp wall to get some air circulating and keep it as dry as possible.

edit, are you sure there is no drain running away from the hole to carry the water away?

 

[Zebra]

Yes my french drain drains into the hole, but the hole was always full of water! All the gutters on the front used to drain into it, and the gutters on the back used to run under the house and out of the top pipe you can see. The amount of water that my french drain contributes to the quantity of water is negligible.

The plan is to create a proper soakaway for it all by extending this pipe and diverting it all, if the hole gets filled in, but I will tackle this when the hole's fate is decided!

I can't see an overflow pipe running away from the hole, no. It wouldn't surprise me if there wasn't one. The yard gully next to the side door went nowhere, and simply dumped all the water under the slab a foot from the house. Will get in the hole tomorrow and have another look. Need to borrow some wellies!........ Thanks

 

[middi]

If there is no dpc in the wall then I would make sure that any surface water would be chanelled away from that hole and away from the base of the building as fast as possible. You may need to re-arrange all the surface and guttering water to be piped away at least 5 metres away from the building, preferably towards a downwards slope, into at least 2 cubic metres soakaway or into public rainwater drains if possible.
Then you can filll the hole.
Having done all this it may not exclude the possibility that a leaky mains water pipe or an old blocked surface water clay drain my be causing problems in that corner of the house.
There is no need to panic, just approach the possible causes one at the time and you will solve the problem.
At best it may be just a case of diverting the rain water as described above, at worst you may need to insert a new dpc in the wall ( not as bad as it sounds if done systematically half metre at the time and some sections may need to be done from within the building )

Middi

 

[Flyfisher]

It may or may not be the source of the problem but my instinct would be to arrange the drainage of all that water some way from the house. At present, the french drain (a good thing) is just concentrating all the water from the house walls into a single point further along the wall (surely a bad thing).

 

[Zebra]

Well I got into the hole, and emptied it. What a job!

Pulled out rubble, silt, water. There is an overflow, but I don't know where it goes to yet.

The walls are cement but the bottom is clay, so the hole is not water tight as I thought.
Why would someone build a hole full of water that close to the house?!
It seems obvious now, that is most likely the cause of the damp in the wall, and the fact that it's been like that for years is why the corner of the timber frame rotted.
I will work on diverting all that water elsewhere. Thanks for your input, this has been really helpful.

 

[Penners]

Well I got into the hole, and emptied it. What a job!

Judging by that photo, I see that you didn't manage to borrow any wellies!

Why would someone build a hole full of water that close to the house?!

You say that the hole has a clay bottom. Is it remotely possible that it could once have been a well, which has been filled in, or has silted up, and was subsequently used as a drainage sump (as many old wells are)?

 

[MdB]

I think I would think twice about filling it in - even if you divert all the pipes going to it elsewhere.

If you fill it with rubble, the water level can still rise to what ever level it wants to. This might be potentially high enough to keep the damp in your walls.

If you leave it as is, you can a) see what level the ground water is at and b) potentially fit a pump into the bottom to remove the water so as to lower the water table locally. This may be enough to cure your damp problem.

 

[Zebra]

Judging by that photo, I see that you didn't manage to borrow any wellies!

But Penners, as well you know, impermeable barriers serve only to compound the problem, we need to let the moisture up and through!
Yes it could have been a well. The cement lining looks 20th century, but I understand from the neighbour that this was once a farrier or blacksmiths cottage, and that part of the house is of a very rough construction and looks like it could have been an animal shelter or perhaps a farriers workshop. But even so, why would they dig it so close to the house! They would have had rising damp in that corner for centuries!
MdB, that sounds very sensible, filling it with rubble does sound like a bad idea. If I get a builder in to rebuild the side extension I suppose they would advocate filling it with concrete? Then the water table would return to its natural level around the concrete lump? I'll keep monitoring it for now and see what it does....
Thanks all!

 

[Penners]

why would they dig it so close to the house

Well, the house may have expanded towards it, over the centuries. But the closer the well is, the shorter the distance that you had to carry the water!

 

[robgil]

It's cement lined isnt it? This might make it a fairly recent addition to the house.

 

[Flyfisher]

I'm wondering if pumping out the groundwater as it fills the 'well' is such a good idea. Could such a thing affect the stability of the underlying soil - at least until a new equilibrium is reached? A bit of damp might be preferable to a bit of subsidence.

But I'm just wondering** - I have no particular expertise. Are there any structural engineers/groundwork experts here?





** I do this a lot. Rather too much I suspect.

 

[MdB]

Yep you're right Flyfisher. Maybe lowering the level with a pump a bit may be a better solution. Maybe to the lowest height it gets to during the summer?

 

[JoceAndChris]

Interesting thread. Just on the "why would they put a well or drainage point ( for rainwater harvesting?) so close to the house" point I think this was very common. We have just the same here, both a sunken well in the floor and a rainwater pit adjacent to the house - both part of the original construction, and both having clearly caused damp for centuries.

I don't think attitudes to damp were remotely the same as now. Now, there's a real panic and kind of zero tolerance towards it. But in years gone by I just think they put up with it, along with all sorts of things we'd never tolerate today.

Good luck with diverting the water away from the property, something we also need to do with our rainwater pit. I'm sure the house will greatly benefit.

 

[Flyfisher]

I don't think attitudes to damp were remotely the same as now. Now, there's a real panic and kind of zero tolerance towards it. But in years gone by I just think they put up with it, along with all sorts of things we'd never tolerate today.

I think that's absolutely spot on.

 

[middi]

I agree. Damp, to us, is slight flaking of paint or discoloured wallpaper.

Damp, up to the end of the 19th C, was classified as having more than one bucket to catch the drips :wink:

Middi

 

[Zebra]

both a sunken well in the floor and a rainwater pit adjacent to the house - both part of the original construction, and both having clearly caused damp for centuries

Interesting. Of course, there are others on here who have wells within the house, aren't there... Surprising though isn't it - in days gone by they might have tolerated damp walls but to allow damage to the timber frame?! I suppose when the walls and ceilings were plastered and the outside rendered they wouldn't have known. Also I'm sure that the person who dug the well, as well as the person who built the house, didn't think that in 2011 the house would still be standing, and a bunch of people all over the country who've never met would be discussing what to do about it!

 

[MdB]

Just to be pedantic, surely wells don't cause damp? Digging one next to your house will potentially lower the water table (a bit) if you keep on taking water out of it. Rain water collectors / wells that have been turned into soakaways can on the other hand raise the water table and cause issues.