Reducing water getting into cellar

[shef61]

Hi,

I currently have a number of damp problems, most coming from a cold and wet cellar. The biggest problems are that the two coal chutes which ventilated it have been filled with concrete (why?) and the garden has been build up with soil, then paving, then soil and then slate chippings, making it higher than the floorboards.

On the advice of a surveryor two air bricks have been installed and I am currently loweing the front garden to put a third one in, I then plan to add a small vent to the top/bottom of the cellar door (so it has ventilation in each corner of the space). If this fails I will put a fan in to actively vent it, but I'll see how this goes first.

My main question is this, while I intend to finish the garden as a gentle slope away from the house, starting 6" or so below the floor and certainly below the new airbricks, would it be wise to dig a trench alongside the cellar wall and backfill it with some sort of drainage gravel instead of mud to improve the drainage of water near the wall, or would this just encourage water toward the wall?

Ontop of that I have read that cladding the exterior wall below ground with styrofoam can prevent water getting in. This seems cheap and easy, does anybody have any information on it?

 

[LanceCorpralJones]

A French drain needs an outlet otherwise it becomes a soakaway. So a trench filled with gravel (use a membrane to surround the gravel to prevent it becoming clogged with smaller particles) with an outlet at one end, or similar would help.
No outlet and the water would simply soakaway into your cellar.

Styrofoam, or anything, fixed to the exterior wall needs to be a full damp-proof-membrane to be of any use. To fix a dpc to the exterior wall will require substantial digging to expose the face of the wall, and I would think it is not reccomended due to the instability created during and after the work.
Additionnaly, it would help to have some cross-flow of air in the cellar. So a shaft of say 100mm pipe sunk into the old chute would help enormously.

Similarly forced ventilation would help. But you need to ensure it circulates the whole cellar.
Don't expect a quick fix. It will take a long time to remedy the situation, only then will it stabilise.

 

[JohnD]

Plenty of air bricks on every side and corner will encourage airflow. You need more than two. There is almost always enough breeze to blow through. You can get Z shaped air bricks where the inside aperture is lower than the outside.

The slope away from the house will also encourage rain to run away, not towards.

My neighbour successfully used a pebbled ditch against his cellar wall to prevent damp soil contacting the brickwork. Only if your french drain collected extra water from elsewhere would it make things worse, and your new garden slope will I think prevent that happening. You can dig a pit beside the house to see where the water table is. A french drain will not cause the water table to go higher, even if it has no outlet. You could even pump it out if it fills with water. The water level in a french drain is never higher than the water table, so will not be higher than it is now, plus you will not have wet mud pressed against the wall.

Cladding the face of the wall is not as successful as you might think, because water continues to travel upwards into the wall from the foundations. If you can expose some of the wall to the air, it can lose water by evaporation.

 

[TheVictorian]

Where is the damp problem showing itself?

I'd start by doing the right things to restore a bit of balance, lower the outside ground level to where it should be.

Cellars in old houses should be cold, if it's warm then there isn't enough airflow! They will also always be slightly damp as the walls are below the ground level.

With my cellar I made sure it was properly ventilated and then tanked one external wall with slurry to stop some specific water ingress. I now have a fairly dry and well ventilated space that serves it's original purpose.