Advice needed damp in wall which is underground level

I am looking at purchasing a house in Brittany. There is a problem I have been warned about even before I look at it. Water or damp coming through one of the wall due to it being under ground level. The problem I can see is that the wall of the house is on the boundary of the land on two sides. One of the sides (the pinion end) is half under ground level, the ground wouldn’t be mine it would be part of the neighbors garden.
So my questions are/:

  1. What sort of work could I do to solve the problem of water ingress or damp coming through that wall?
  2. What rights would I have over my neighbors land, to dig or remove the earth away from my exterior wall to put some sort of membrane if possible wall on the exterior to eliminate water / damp penetrating my property.
  3. What should I look for inside to see just how big a problem this has been and is going to be.
    This seems to be the only problem with the property except for the normal electrics not a norm it is on tout au gout so no fosse septic problems. Any advice as to what I shoild be looking for specifically when I go view the house next week?

With the massive caveat that I’m not a builder.

Live with it? That’s why a lot of houses in Brittany only use the ground floor as garage/utility space.

Otherwise, dig out all soil treat the wall to make it impermeable and/or install a waterproof membrane before replacing the soil.

None, unless it has previously been agreed. Not that stops you asking nicely.

Damp or rot in timbers would be the biggest issue I guess.

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Thank you

Why buy problems?

My pleasure, though I don’t think that I helped much :slight_smile:

Oh, I forgot, if you want to make it watertight you’ll need to consider the floor as well - making the wall watertight but leaving the floor permeable will probably move the problem rather than solve it.

Seriously though most Breton stone houses do not have damp-proof courses and being half built into the side of a slope is very common.

The problem is usually addressed by having the living quarters above the worst of the damp, occasionally to the point of having the front door on the first floor and stairs leading up to it.

Or make problems where there aren’t any to start with.

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I am not sure how big a problem it is going to be yet. I am just trying to find out if it is going to be a massive headache or something I can solve easily.
The problem is I have just sold my property in the Auvergne and am looking for something back in Brittany, but there is not a lot about in the price range I want to spend or area. This property is in the ideal location price a little high for possible problems but that is negotiable; I would rather go see it take a look and see if its workable or not with as much knowledge and information I can get concerning this type of problem , as it is not a problem I have encountered with other properties I have purchased in the past.

We have an old stone house here with one wall below ground level and some damp at times. What to do depends on the severity and nature of the damp (rising or penetrating) and you should get some expert advice for your specific problem.

Generally speaking, penetrating damp may be fixed with tanking, creating a waterproof barrier on the surface of the wall. This will not work for rising damp, which may then find its way out by going higher and higher up through the wall. Injection damp courses may help, but tend to be temporary.

Billy’s advice is good, and it’s quite possible to live with a slightly damp house by making sure that there is good air circulation and nothing is built against the damp walls to trap moisture. If this is intended to be a holiday home, only lived in a few weeks per year then it’s not a great idea, but if a permanent residence then it may well be fine.

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None at at all. You can try asking politely and grovelling if need be but don’t get your hopes up.

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… With a perforated pipe at the bottom (draining away somewhere) and backfill with gravel.

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Unlike modern homes, your old house (and mine) were designed to work with nature - not against it!
Cellar & Basement Damp3.pdf (209.1 KB)
Cellar and Basement Damp recoveredd.pdf (529.5 KB)
Old Houses Deal with Damp by Breathing.pdf (294.4 KB)

My house is built into a hill and has 3 stone walls completely under ground level.
When we moved into the house, the cellar damp was so bad that it set off smoke detectors, cardboard boxes rotted in around 6 weeks.

Now the cellar is completely dry and useable.

What we did was:

  • rip out all the materials that were covering vents;
  • add an extra closable vent to two of the cellar doors;
  • remove some of the cement mortar from the front wall and replace with limecrete;
  • put a thick layer of limestone gravel over the earth floor.

May I suggest that you google “Peter Ward damp”.

Meanwhile I’ve attached a couple of documents that may be of interest.

Cementing the floor, tanking the walls etc is probably going to make the situation worse


Thank you It would be full time residential

Thank you for this information very helpful going to look up Peter Ward now and read the pdfs


When we bought the house it was obvious from the 10" gutter running around the external walls of our cellar that the builders did not expect the space to be bone dry.

But it was pretty OK most of the time without too much of a problem.

The main weird thing was cardboard - it didn’t rot but the damp was sufficient to cause the adhesive that holds it together to fail - so anything cardboard delaminated if left down there long enough.

However in the last two years we’ve had a much worse problem, I think that it has been much wetter in our corner of Brittany and the ground has saturated - to the point that we have been able to see water literally appear on the sections of cellar wall below ground level and run down into the gutter - something we just did not see previously. The result has been a significant problem with mold down there.

This hasn’t been helped by not being able to visit because of Covid so we just haven’t been able to open the house up and get it aired - despite continuously running ventilation the house has been very damp and, not surprisingly the main house has had mold growing on surfaces as well (nowhere near as bad as the cellar).

I’m making my 2nd visit in 6 weeks which helps enormously and we’ll be back in August - after that not sure but hopefully well be back to a more normal schedule of fairly frequent visits.

In the mean time I’m damp-proofing the cellar - not in the way that was beng talked about but stuff like bringing the chipboard shelves up , cleaning the surface, letting them thoroughly dry in the sun, treating with fungicide and then painting so that they won’t soak up moisture, plus getting rid of wood, cardboard and anything else which will rot and moving other stuff to storage boxes (with dessicant to keep the RH down).

I’ll read the documents Nigel posted later, might pick up some tips - in the meanwhile I’d tend to agree with him. Don’t try to make an old house completely bone dry.

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Really it sounds like you need to visit to get an idea of just how damp the place is. Since you’ll be living there it’s entirely possible you can work with the house to keep it ventilated and prevent moisture becoming an issue.

When we looked at houses last year, all were empty and we found some were very damp and clammy while others were nicely dry feeling. It might be good to put a shortlist together & have a visit-a-thon to get a feel.

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I should have mentioned that it took between 18 months to 2 years for the cellar to dry out thoroughly.


The problem with water (i.e. damp) is that it will always seek to go somewhere drier, so the drier a wall gets, the more the damp will rise. Our house was built around 1750, and there are parts that suffer from rising damp, the more so this past month after weeks of around 28-30° C. A small area of grey concrete floor in an unused part of the house has, as usual, gone black where the damp is rising into it. In the winter it’s usually grey.
The main part that we live in was given a second, interior, skin by the previous owner (a mason) to make what is effectively a cavity wall using 4cm-thick red terracotta bricks stood on end, and a superb job he’d done too. So while there is evidence of damp on the outside it’s fine on the inside, and the already very thick walls look about 10cm thicker.
I was once told that rising damp will stop at a maximum of something around a metre and a half above ground because gravity then takes over.
In the UK we lived in an Elizabethan-era stone cottage, and all the walls on one side were build on flagstones sitting about a metre below ground level. However, below the top 15cms the soil was almost pure sand so drained completely and the interior was dry.

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Thank you all the information that has been given has helped me feel more confident about my visit on tuesday. I will see how it goes.

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Used this method many times during my UK builder days and its name, a French drain!

Its closer to 1 metre but if you are RICS trained then rising damp doesnt exist. :joy:

The workshop of my boatyard in Devon was half below gnd level. It was about 30m from the sea wall. On a really big high tide [6m rise of tide on a big Spring] , the ones that used to just creep over the top of the sea wall, the pressure of the water in the ground used to start jets of water springing from holes in the tanking in one wall !

But that was not very often.

When I bought the place I did wonder why all the power points were at shoulder height.

Tanking. It would be excellent to do as has been suggested above, as well, re the exterior but you can contain the damp by tanking the inside of the wall. This is what I had to do with my house in Bristol which showed red on the damp meter at +/- 1m above floor level because next door [party wall] had no d.p.c. Tanking this wall from my side solved the problem.

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