Mysterious damp under the stairs (1920s detached)

[spidershavetoomanyknees]

Ok, first things first: yes we will be getting a plumber (?) to look at this, but I know how quick the great Mumsnet is at resolving this sort of mystery. So....

We definitely have damp in the understairs cupboard, inside a fitted cupboard sort of situation. It smells (not of rotting, but like a very intense "old book" sort of cellar smell), the paint is coming off the walls (it's sort of chalky textured and falls off when you poke it), the woodchip laminate style floor is kind of "popping" upwards, and the humidity doodah says 74%. It's an exterior wall. Outside there does seem to be a corresponding "hump" where the bricks are darker and I'm assuming are damp.

However. There are no water pipes that I'm aware of near there (the one running outside is gas going from the meter to the boiler). Although it does seem to have condensation or rain dips underneath it, I don't think that would be enough to make the wall damp and surely it would be all the way along. The first-floor bathroom is at the other end of house (at the back) whereas this is right at the front. So at the moment I'm stumped. Any ideas?

Photos attached of:

1. the Hump of Darkness outside
2. the wall above the hump of darkness outside
3. under the stairs with damp wall, also showing the popping floor

Our current immediate plan involves removing the fitted cupboards, then try to lift the flooring and see what's underneath. Also locate a plumber who would be able to do something or investigate more thoroughly.

Weird to see those engineering bricks step up like that. Looks like you have a solid wall. The window is a later addition or widened at some point, and you’ve had some brickwork done, though maybe it looks like that because of the damp bricks.
Up in the gable there seems to be an overflow pipe from the loft. Investigate that.

Presumably you have water connected in the area of the window, as you have a waste pipe coming from the wall, so could there be a water pipe running under the floor, that is leaking?

I would take the floor up and investigate, as looking at the sloping wall, it looks like rising water/damp to me.

@C4tastrophe ok. What sort of thing would we be looking at in the loft? I think that's the house water tank. No idea about the rest of what you say as we've recently moved in, but very interesting 🤔

@Hallmark1234 yes, that's the kitchen sink behind the window. Will see what we find when we lift the flooring in the hallway... thank you. The sloping wall is the underside of the (extremely creaky) stairs going up

I was going to say damp in a cool exterior enclosed space can be condensation from the rest of the house condensing in there and a vent would help.
but from those photos you have a different problem. There’s the large exterior damp stain which has to be water coming from
somewhere. Is a gutter or pipe pointing straight at that wall from above? Failing that there must be a leakage coming up from underneath.

Is that pipe dripping? The water tank usually/could ( need Piglet John) have a ballcock arrangement that may be allowing an overflow, just like in a toilet cistern.
You don’t have gutters, and the ground level is fairly flat, so it’s likely to be a leak or that pipe.

DO check you don't have a boarded over cellar full of water.

@Ariela is that from bitter experience..?!

@C4tastrophe it doesn't seem to be dripping, but maybe if it does come from the water tank it'd only drip when in use?

The leftmost attic pipe is approximately above the damp hump outside

The damp patch seems to be all recent or non original brickwork. Or is it just the wet making look like that?

@C4tastrophe I believe all the brickwork is original, by the feel of it. The photos make the damp areas clearer even that by my eyes outside, if you see what I mean.

@C4tastrophe I'm looking at it again and I see what you mean... those look awfully flat and clean to be 100 years old. Will take another look in the daylight tomorrow

Water doesn't leak upwards, it finds the lowest point. Is there a cellar or a crawl space under the ground floor where you can see any pipework that goes through that understairs cupboard? If the flooring in that cupboard has buckled due to damp you may as well pull it up and see what's going on, i.e. where it's wettest. It's highly likely there's a pipe in that wall, possibly from the central heating system and that's what's leaking.

It could just be that the damp proof course has failed in that area. It does look like rising damp from the pics. Possibly it was damaged from
them pipes or is it wire attached to wall? Only takes some small damage for the damp to get in- that’s why it would be in that inverted v shape

That's quite a lot of damp, and could be leaking water from inside house. If you have a water meter, turn all taps off, and check that meter stops. If meter still turns then you could have a leak. Sink near to wet wall must be a contender.

That's a water leak somewhere in that region.
Had one at my late parents house, it was caused by a low grade drip leak at the bottom of the loo tank where the overflow comes out. The water soaked up both side (indoor) walls as well as the back (exterior) wall behind the tank. Flakey paint on walls at the tide mark like you describe.

It could be from a leaking radiator pipe if there's now water pipes in that area?

I would also suspect leaking pipe in that wall. The highest part of that hump is where I'd investigate first, internally.

Where does the service pipe from the street up to and into your house run? Generally they run in a straight line from the external stop tap to the kitchen sink.
We had a leak under our house from the old lead service pipe. It was like a lake under the floorboards!

So it looks like the outside brickwork and pointing is the culprit - it just falls out when you brush it and there are some holes. So we're removing the old fitted under stairs cupboards, the internal plaster, flooring, and getting a brickie in to sort the external wall

@spidershavetoomanyknees

I saw someone with a damp patch similar to this several years ago, and it boiled down to a spring running beneath their house that they didn't know about. They had a lot of rain, and it kind of overflowed/burst slightly, and the foundations got affected, and the side of the house looked like yours...

Do you have a plan of your house or an ordnance survey map of the area? It may show streams and brooks and springs.

Do you have a cellar? Sorry if you have said. (I can't see you saying you have though.)

Did you check that the overflow from the water tank in the attic isn't discharging randomly? That would make the same pattern of damp on the brickwork as you see and cause the pointing to degrade.

Has someone drilled through a radiator/water pipe when adding the outside light?

How are you getting on @spidershavetoomanyknees?

At the moment we're still just monitoring - we've had someone to check the pointing and they reckon it's fine. The fitted cupboards have been removed along with the plaster and the old laminate flooring... which was on top of plastic sheeting, on top of the original tiles. So that can't have helped.

With all that removed, we were able to see the floor visibly drying out with the help of a fan and the humidity is now down to ~65%. So far so good. Now to replace the hallway window which hasn't opened in years and won't have helped with humidity. In the rest of the hallway we're removing the (3 layers of) wallpaper and the wall behind seems fine.

@Geneticsbunny doesn't seem to be any sign of this happening, but we are getting the water tank and the rest of the system looked at in the next couple of weeks just to rule that out for sure