/ Damp in house - advice about drain pipe

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NottsRich on 13 Jun 2017
I've got a small damp patch inside the house, not too bad but needs fixing. On the outside in the same location there is a downpipe from the gutter which was blocked and hence water was running down the external wall. It's now unblocked and working correctly. However, I'm concerned that the blocked pipe wasn't the cause of the internal damp. Photos here:

Q1. There's a hole around the downpipe where it enters the tarmac (public pavement). Is this a problem? I assume that it just allows a bit of additional water to enter the drain/sewer. The angle of the pavement means that water runs away from the wall rather than towards it and down the hole, i.e. it's not overloaded. I'm more worried about debris getting washed down it and blocking it further down.

Q2. The rendering on the wall doesn't extend far enough down to meet the tarmac (public pavement). There is a feasible gap where water could contact the brickwork. Is this a problem? Should the rendering meet the tarmac, or is a gap intentional?

I'm tempted to fill the gap around the downpipe with some mesh to prevent stuff falling down the hole, and then put some tarmac over it to cover the hole, and bridge the gap between the rendering and pavement. Would this be worthwhile, make no difference, or actually cause harm? Anything better than tarmc from a bag for this job?

I don't want to call a damp company and get taken for a ride, so I'm trusting UKC on this one!

Many thanks.
SuperstarDJ - on 13 Jun 2017
In reply to NottsRich:


I'm also dealing with various damp problems in Nottingham in an old house so have been reading around and taking advice. My opinion, for what it's worth.

Looking at your situation I would probably leave it alone. If the damp you have was coming from above and you've dealt with that problem then wait and see if another problem appears. I don't think that the hole you have will be doing any harm though I don't think blocking it up will make much difference.

I found this site useful in understanding what's happening at my house. Hope it's useful.


NottsRich on 13 Jun 2017
In reply to SuperstarDJ:

Hi, thanks for the reply! I should have mentioned where the damp is inside the house. It's on the internal wall in the immediate vicinity of this pipe/hole. It's at ground level, and the damp has risen up perhaps 30cm and spread 30cm each side of the pipe. Based on the location of this internal damp, it's coming from gound level, not above. It therefore not due to water running down the wall, but of water soaking in somehow around the base of the wall, which is why I'm suspicous of the gap and open hole. Around the corner are a couple of air bricks. I'm also wondering if rain is getting blown through them by the wind. I could fit a louvre or something on the outside to try to reduce that chance.

It seems like it can take a long long time for things to dry out once the source of the damp has been removed. Rather than take several years, I'm tempted to do everything I can think of now and hope that one of them works. But I take your point to leave it alone and see what happens. I'll have a read of your link, thanks.
Trangia on 13 Jun 2017
In reply to NottsRich:

a) The render is probably bridging the damp course and if the dampness at the base of the wall had been going on for some time moisture could well be rising up the wall by capillary action between the render and the wall,

b) There cracking in the render suggesting loss of key. Does this loss of key extend further up the wall? Tapping it and listening for a hollow sound should tell you.

c) What is the wall? Brick or stone? Where is the dpc?

A1 Difficult to say without digging out and investigating.

A2 Ideally there should be a gap to reduce capillary action see a) , but the render needs to be sound so that the dpc isn't bridged by it. If the underlying brickwork or stonework is of facing quality, then then ideally the render should stop just above it, to reduce the risk of bridging.

Blown or hollow render can lead to damp problems.
jkarran - on 13 Jun 2017
In reply to NottsRich:

Solid wall or cavity? Either way if it's rising damp in that location it's probably water from the roof saturating the ground around the bottom of the downspout rather than continuing down the drain. I had similar problems with cracked earthenware gullies and a broken joint in the soil pipe. At least mine were on my property and easy enough to dig out, I don't know how you fix it when they're in the road. Actually one of my downspouts is on the neighbor's property and that one is leaking back into my subfloor too. I've filed that mentally in the 'too much hassle to fix' box for now.
PaulGraham - on 13 Jun 2017
In reply to NottsRich:

I’m not a builder but I’ve had a couple of leaks. So FWIW:

1 If an interior wall gets damp it spreads out slowly through the plaster (assuming you have plaster!) for several months and paint will bubble/peel. You need to wait until this stops before preparing the surface and redecorating.
2 A plumber who attended my last leak said to leave the area exposed to air for 6 months before re-boarding and insulating the area.
3 It looks like the tarmac around your external downpipe is complete on the far side of the pipe. If a hole was put there by design I would have expected it to be symmetrical around the pipe and the pipe to go through a grating. If it were me I’d fill it in because once water builds up in an area it can only evaporate or leach into the containing materials.
4 Is your wall single brick/stone or double brick with an airgap? If the latter any leak will have taken longer to get through and longer to dry out.

I’ve found this forum helpful for building/DIY issues:

bearman68 - on 13 Jun 2017
In reply to NottsRich:

I live in a stone built house, and a similar issue has resulted in a damp patch on the inside of our wall. It's taken so far nearly 3 years to dry out. 3 years.
So, yes, a leaking downpipe in a stone house will have a huge effect. Cavity wall, I would expect it to be much smaller, but I would still think it's a concern.

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