Terraced house and damp

[TheAntiBoop]

If in a terrace one neighbour puts full damp proofing in the basement - is it likely to cause a damp issue for the neighbours? No previous rising damp.

[PigletJohn]

do you mean fixing waterproof plastic sheets to the walls and floor?

[TheAntiBoop]

Yes - the bobbly wall stuff and concrete floor with plastic

[TheAntiBoop]

Sorry for rubbish technical knowledge here!!

[PigletJohn]

sounds like they are doing a proper job, and will have a sump pump under the floor to suck up the water that trickles down (as it will no longer be able to evaporate, it will collect).

A long as they have the pump, the water table will probably be unaffected, but your party wall on that side might be damper because there will not be evaporation from their side.

Verify that your basement ventilation is good. You need airbricks or other vents on the front and back of the house, with an unobstructed airflow so that the damp air can blow out with natural air movement.

If the vents have been blocked e.g. by extensions, conservatories or raised paving, look at reinstating them (this would apply even without your neighbour's work). Do not put any stored items standing directly on the floor or touching the walls, especially stuff in boxes unless they are plastic crates. You can use plastic shelving units.

[TheAntiBoop]

Would it be an electric pump? Sorry I don't fully understand! If there is no pump would that cause the water to possibly run to the party wall? Can a pump be fitted retrospectively?

So on one side it's a concrete floor with underfloor heating in it. Other side is a suspended floor

[PigletJohn]

there's a picture here about half way down.

The membranes prevent water from entering the protected room, so it runs down the walls and collects under the floor (there should be a gap) and when it collects into enough, a float turns on the pump and it is pumped out to a convenient drain. This tends to happen more in rainy weather. If there is only a bit of damp, rather than visible water, it may possibly drain away through the floor without collecting into a pool. The pump prevents trapped water rising up behind the membrane.

[TheAntiBoop]

Oh I see. So in theory the water could collect behind the membrane and then go through the party wall and cause damp next door?

It isn't damp down there (it's not below ground at any point) so I can't imagine much water will gather. Do you need a pump or are drainage channels sufficient?

[PigletJohn]

in a terrace, it would probably form puddles on the floor, and if it couldn't soak away, would make the next door floor damper than usual, if it is at the same level.

If you don't already get puddles then you probably won't after the change.

You said it was a basement so I understood you to mean it was below ground level.

If you mean it is a new excavation under the neighbours' house, and you don't have a cellar or basement under your house, then it is most unlikely that water would rise up to ground level, unless there was a burst pipe or something.

You need a pump to lift water if it is below ground level. If it is above, you might be able to run it out to a drain; but if it is above ground level it should not get much damp.

[TheAntiBoop]

No sorry I wasn't clear - more lower ground. It's an old terrace on a hill so the front vault is below ground but the back of the basement is garden level. So the room with the membrane has no earth abutting it iyswim

Thank you for the information!!