Damp. Cavity wall insulation?

Beartricks

Hi,



We repainted the front room earlier in the year and just painted right over the coat below. Prior to this, there was no visible damp.



It has rained slightly since then and we've had a bit of damp since on the front, North East facing wall. The last couple of weeks it has poured and the damp has got a lot worse. Originally I thought the problem was rain collecting on the flat roof above the bay window and running down the walls but someone suggested that it may be cavity wall insulation. It could also be penetrating damp making the insulation wet too.



There is an almost straight horizontal line of damp about four feet up the wall and absolutely nothing above. This indicates to me that there is something structural at that level. Below that the damp is patchy but there is quite a bit just under the window and some patches at skirting board level.



The damp gets worse when the central heating is on but the pipes are all under the floor not in the walls. There doesn't seem to be any damaged pointing outside as far as I can see but I haven't had a thorough look yet.



Here's my guess: The horizontal line is the top of the insulation, or a void where it has slumped. There's condensation collecting here as the wall will be colder. Similarly the points under the window are either letting water in directly or its condensation above the insulation. When we put the heating on, it raises the temp a few degrees increasing the condensation. I'm likely wrong as I have no building experience.



The house is owned by a relative. We pay rent but also tend to organise repairs ourselves and bill them for it. We don't know if there is cavity wall insulation but are trying to find out. What baffles me is why the damp only started showing up after we painted.



Any ideas or is it time to get a surveyor in?

FreeBear

Check your gutters and downpipes. If possible, rod out the underground pipes as far as the soakaway. Next time there is a real heavy downpour, nip outside and see if the gutters are overflowing.

I have cavity walls (just the ground floor) with some CWI installed - Did have a blocked drain which was causing the downpipe to spew out water and resulted in a damp patch on the wall. Fixed the drainage, and the damp has disappeared.

Doozergirl

I'd look for the cause. Cavity wall insulation doesn't cause it, exactly, you still need a situation for damp to arise.

If it's worse with rain then that suggests a leak, certainly.

Straight line about four feet up?
Previous damp proof course with waterproof render up to 1 metre possibly.