Damp patch on wall

[simon_m]

Hi all, I have a damp patch in one place on the back wall of my house. I installed decking around 18 months ago and although it is below the DPC I did butt it up tight against the brick work. Thinking it may have been this causing the problem I have cut the decking back an inch so it is no longer touching the wall but the damp patch is still there.

I have examined the wall and noticed that the damp patch is at the bottom of where the soil stack is, the stack is in side the wall. We had wall insulation installed around a year ago and I noticed where they have drilled the holes is in line with the soil stack, so I am thinking that maybe the have drilled through the stack and water is collecting inside the cavity, is this possible? There are no signs of damp inside the property, would the stack run inside the cavity? thanks in advance.

 

[JerryM]

the damp could be coming from the outside ie the garden if for example you put a PVC sheet under the decking which has ended up sloping towards the house and specifically towards the area of the damp - i doubt this is the case but you need to exclude it. the decking itself will have nothing to do with it.

i think the soil pipe is a possibility. i can't understand though why if water is getting into the cavity why the internal wall isn't damp.

so it may be drains.

suggest initially you carefully dig out around the wall where it's damp (where the soil pipe exit's the house) to try and confirm the soil/drains are not leaking - cracked drain pipes are quite common and can cause damp & foundation problems.

if nothing found then feel you're going to need to take a brick or 2 out where the holes were drilled be able to see inside the cavity. can you access under the floor on the inside of the house as this may also give some insight.