Draining a cavity wall

[MarkSmith]

Hi,

I am doing a cellar conversion. One wall is up against soil, and gets a bit damp in one corner. I don't know how it's drained - it certainly is somehow because when it rains hard you can see (through vents) water pouring down the inside of the outer skin, and it's certainly not filling up or pouring out into the room - but nonetheless a bit of moisture gets into the inner skin and into the room.

Plan A (suggested by three builders) is to Synthaproof that wall and the neighbouring walls. Just keep the damp in the cavity to drain by whatever means it does now (and has done for 80 years). Sounds OK.

However can this be improved on, fairly easily? While the room is a building site anyway I thought I could add a drain to the cavity. My idea was to drill a 100mm hole at the base, resin in some 100mm drain pipe, sink it under the floor, sloping downards, out to behind the house. House is on a steep hill so even with a 1-in-10 fall it would still be above ground by the time it gets out the back.

90% of it can be straight, but the last 30cm will have bends and will (because of the construction of the room) have to be set into reinforced concrete (to be added next month, so now's the time).

One concern is that it might fill with debris over time, and block. Putting a U-bend in, in a cavity under the floor, accessed by a panel, would not be impossible.

Any thoughts on this please? Good / bad? Forget it? Better suggestions?

Thanks,
Mark

 

[noseall]

I can not picture your scenario?

The one thing i find a little troubling is this cavity drain thing. Is there some kind of hidden drain that is taking the water away from the property? If not i would be alarmed.

Which ever way you decide to carry water away fro your property, it is still your problem. A soak away is normally dug no nearer than 5m to any structure.

I would also use strong mortar as opposed to "resin" when sealing up any holes in prodigiously damp masonry, as you will have greater success.

 

[MarkSmith]

Thanks for the reply Noseall.

Which bit is hard to picture? I'll describe it a different way, see if that helps.

Semi-detached house. This cellar room has four walls, A, B, C, D.
Cavity wall A is at the front of the house, soil level outside is right to the top of the wall.
Solid wall B is against the neighbour's cellar.
Solid wall C is up against anothe other cellar (mine).
Single skin wall D is up against my other cellar (mine).

When it rains, water runs down the inside of the outher skin of wall A and somehow escapes from the bottom of the cavity. Could well be a hidden drain. Could be a soakaway directly under the wall, I suppose - not saying that would be good, but I don't know what's there so it's not out of the question. The "problem", inasmuch as there is a problem, is that it doesn't drain away quite quickly enough - presume it pools there for a bit and soaks through into the room, meaning the wall is damp (in that one corner).

I suppose another question to ask would be, if you came across a cellar room with a damp problem in one corner, caused by poor drainage of the cavity, what would the options be?

There are several soakaways in the back garden - can easily direct it into one of them. (In fact, complicated to explain, but there's already a pipe through the cellar taking the rainwater from the front gutters into a soakaway in the back garden. Thought was to add the cavity drain into this.)

Thanks for the mortar tip!

 

[noseall]

It is extremely rare to encounter a subterranean structure that did not have some kind of damp problem.

 

[MarkSmith]

Oookay. Right.