Rising damp patch on interior wall

[nothernexposure]

Sending the bat signal for @pigletjohn... I've got quite a big damp patch on an interior wall and I'm wondering if it's being caused by a leaky pipe under the floor boards. There's a bathroom at the rear of the house and the kitchen at the front and the damp wall is in the middle of this. Any thoughts on if it is likely to be a leak causing it and how would I investigate? Theres hardwood flooring downstairs so I want to avoid pulling stuff up if I can. Pictures and diagrams can be provided! Thanks for any help.

Probably. Post some pics.

Thank @PigletJohn do these help at all?

is it a concrete floor?

stand back and take a wider pic of the whole wall (both sides) showing the shape of the patch.

was was the nearest fireplace or chimney?

how old is the house?

have you got a water meter?

do you know where the outside stopcock is?

Thanks. The house was built around 1780. The damp is only showing on 1 side. The room it's in is lower than the other rooms downstairs. I've attached a drawing of the layout to show where the chimney is. I've no idea what's under the wooden floor!! No water meter and I'm not sure where the outside stop cock is. Hopefully the pictures below show the patch although they're not great pics as the lighting is rubbish.

so as I understand your floorplan, the damp wall backs onto the staircase. Do you have access to the space under the stairs?

take your shoes off and jump and and down on a few wooden floors and a few concrete ones. Sit on them and hit them with the heel of your hand. I think you will soon recognise the difference.

A wooden ground floor will have a void underneath which should be ventilated by airbricks in the external walls allowing air to flow underneath and evaporate away some damp from the ground.

Hi @PigletJohn. Yes, the damp wall backs onto the stairs. The other side is picture 2 in my last post but I dont think they directly back onto one another as the stairs are a good few inches longer than the under stairs bit in the picture. I think, but still not sure, the floor underneath sounds like its concrete. I've seen airbricks at the back of the house but not the front. Thanks

do you think there is a void or cupbord under the stairs? how thick does the wall seem to be?

is there a bathroom above the wet patch?

There's just an open void under the stairs. Originally the bedroom on the floor plan would have been the kitchen, and the void now is just open in the bedroom. The space under the stairs measures 28" however the stairs to the living room side of the wall measures 35". The bedroom wall sounds hollow like thin plaster board whereas the living room wall sounds solid when tapped. I'm guessing there's space inbetween them. Part of the bathroom is above the living room wall but part of the wet patch is under the landing. We have had damage to the ceiling from bathroom leaks which I hope has been fixed several years ago! Thanks for taking the time with this.

I think the wall may have been drylined on the bedroom side. that would add a few inches of thickness and it would sound hollow. Possibly if the wall was previously an extrtnal one and was rough. this would explain why the surface is not visibly damp on that side, even though the brick wall behind it might be.

As the damp wall is an internal one, the damp is not likely tp be rain related, but quite likely due to leakage.

Let's suppose there is an old concrete floor which was covered up by a previous owner. they might havre done that to conceal damp. unable to evaporate off, and if the house was built before dpcs became compulsory (about 1875 in london but may be later elsewhere) then damp could rise up the wall up to the height where the rate of evaporation equalled the rate of absorbsion. It's possible there will be a dry-looking line near the floor if a damp-hiding treatment has been used.

to test this, you really ought to lift the flooring and look behind it. it's possible to measure the amount of water in a wall by drilling out samples, wighing them, drying them, then weighing to see how much less they weigh. Electrical damp meters are not reliable on masonry because it depends what the materials are. you might see something if you pry off the skirting boards (this needs doing anyway if they are damp and rotting).

you may find traces if you look at, or under, the bedroom floor.

If you can find the outdoor stopcock, you can test to see if there is an audible leak. it might be in the front pavement or back yard depending on local practice. It may bave been hidden under paving by some previous numbskull.

if you do the test using an indoor stopcock, it will only tell you if there is a leak after that stopcock.

It is possible that a leak from the bathroom above has got into the floor. this may take a year or more to dry out.

p.s.

it is useful to outline the shape of the damp with a pencil, and write the date against the line. this will tell you if it gets better or worse, for example in damp weather of after a bath. Photograph the marks for future reference.

if you are unlucky, the drain from the bathroom above might run under your floor.

Thanks. The bedroom wall is an awkward space so dry lining it makes sense. I can see where the waste water leaves the downstairs bathroom but just realised I have no idea where the soilstack is! How would I track down the external stop cock? I've not seen anything outside that gives me a clue. There is a manhole cover at the back of the house, would it be anywhere near there?

It sounds like I'm going to need to get someone in to lift the flooring (not a job I think.i can manage and no other adults in the house to help) and see what lurks underneath....

walk up and down the road.

if the supply comes under the pavement, there will be iron or plastic access harches about 200mm square or round, in the pavement or front garden next to where the front gate used to be when he house was built. Some will have been buried or paved over by numbskulls.

in some districts, there was a service lane or mews behind the houses, and the pipes might run there. in this case, various repairs may be evident where trenches have been dug for repairs and patched up later.

it is not usual to have a man-hole sized cover (though I had one)

also, ask neighbors with similar houses of similar age.

an old house may not have a soil stack of modern design. but will usually have four-inch cast iron stink pipes fixed to the outside of the house, reaching above gutter height and open at the top. they will follow the path of the underground foul drain. pipes from WCs will be visible connecting to some of them . Bathrooms and kitchens may empty into a hopper or gulley which will connect to the underground drain. the iron pipes may have been replaced with plastic.

Oooo! Just found this! It's near what's near the newer kitchen extension and originally might have been near the house entrance. Although its completely sealed shut and does say drain rodding point on it. Is this it?

A drain prodding point is not a stopcock.