Puzzled over damp......

[Feltwell]

Can the collective PPUK brains offer their opinions on this one please....

We'd noticed that in our kitchen in the last week or so a damp area on one wall has been getting much more noticeable. As this area is directly beneath where I know a lot of heating and water pipes run, I presumed I'd got a leak. Picture is below (after I'd had a little exploratory take off of plaster around some heating pipes to see if they were the culprit - they weren't)

So, I took the floorboards up in the room above this morning, and found everything to be bone dry - definitely no leaks from a pipe above.

The outside of this wall has a single storey roof butting up against it, as in the picture below. The roof is only 2 years old, I took some tiles off today to double check and the flashing and soakers all appear to be fine. The roofing membrane is correctly tucked up behind the flashing. The top centre of the damp patch is a good foot above the roof line anyway, so it's unlikely to be a fault there I think.

The outside wall is clearly damp. It looks in the picture below as if the area behind the downpipe is damp - I don't believe it is, I think that's old staining of the bricks. The room behind the downpipe has no damp in that wall and the downpipe appears to be working fine, I tested it with a hosepipe.

But you can see a patch (coming up to a level with the top of the horrible cement patch around the overflow pipe) that looks darker and is damp, I'm sure.

So I took all the plaster off the inside to expose the brick and let it dry - this is the most messed about with section of the whole house, it has gypsum plaster painted with modern emulsion on the inside, cement pointing on the outside, and has generally been b**ggered about with - original window gone and a new cheap one bodged in, internal doorway widened, nasty plastic guttering put up, etc.

You can see the darker damp patch quite clearly. The timber packer to the right, as well as the timber lintel above the window, are both very damp (but fortunately the lintel does not appear to have any rot).

When the main house roof was being replaced, we had a severe storm one night and the temporary waterproofing leaked quite badly into the room right above this area - just for one night. This was over 2 years ago, and apart from some staining to the kitchen ceiling there was no apparent damage and it all appeared to dry out of its own accord quite quickly.

What I'm thinking is that as I can't find any leak now, and this area had no breathability at all on both sides of the wall, is that the water from the storm leak had nowhere to go so has just stayed there, the paint only starting to mark and blister off now. But would it really take 2 years for this damage to appear? Any other thoughts on where the damp could have come from?

How long do you think I should leave it to dry out before re-plastering (with lime of course)?

Gives me an excuse to change the horrible & decaying kitchen window back to a sash I suppose, even though I could do without the expense!

 

[Schoolmarm]

I think that the wet cement pointing around the overflow is very suspect.

Is that overflow leaking inside the wall? Is it tilted up slightly as well?

Does that cement ever dry out?

It is just so near your damp patch inside.

 

[Feltwell]

I wondered about that, but the overflow appears to be bone dry, if badly fitted. It comes via a very long and twisting route from the central heating header tank in the floor above (the attic). I think I'll take the cover off for a bit and just check for a few days that the level never gets near the overflow. I'll keep an eye on the cement patch as well to see if it dries.

 

[Schoolmarm]

Plus, if it was tilted up ever so slightly, and there was a teeny crack around the top of the pipe where it comes out of the wall, all rain etc will run back into the wall.

 

[Feltwell]

It's a good point and I'll check, it may not be helping. I can't see it being the prime cause though - it's been quite dry here lately and the obvious damp patch has only recently appeared.

 

[Jon Maine]

Do you know if that down pipe is clear, That could be a potential issue if it is overflowing in storm conditions. I had to clear one here a few days ago which was blocked by sticks dropped by birds with a bit of moss etc on top.

The overflow is worth checking out as it should really angle down from the wall, but the damp seems to extend far above that so maybe not.

The stepped flashings seem to be a little step also on some of the angles which can cause a problem too.

Good luck

 

[Lime]

Possibly two causes.
>The header tank overflowing intermittently.

If you examine the header tank inside and you see a mark at the level of the overflow you know you are having or have had problems.

>The downpipe leaking in some way.

The downpipe could be blocked as has been suggested.

It could be split/rusted through at the back in a way that can't be seen.
The split/leak could be much higher than the wall bracket and running down the outside of the pipe.

Or it could be coming from the guttering and running down the outside of the pipe until it meets the bracket.

 

[Penners]

The problem with that area is that there are so many water-related things going on. You've mentioned checking a number of them, and pretty well all points have been covered by othe rposters. But for what it's worth, here's a bit of a summary think-through:-

1. You are, I presume, absolutely 100% certain that there is no plumbing leak, related to the two white-painted (heating?) pipes that descend from the ceiling. No possibility that there's hidden leak somewhere higher up - perhaps where they join other horizontal pipe runs?

2. Like Schoolmarm and others, I wonder whether there's some sort of problem relating to that header tank overflow pipe. It appears to be at just the right height to be causing the problem. It may be dry on the outside of the wall, but I don't think this necessarily precludes the possibility of water running down its outside surface, inside the wall. Is it possible that there's a leak where the pipe enters the tank, that's allowing water to trickle down the outside of the pipe?

3. As mentioned by Jon and Lime, are you absolutely certain that there are no leaking joints or blockages in the surface water downpipe, or in the gutter at the top of it?

4. I'm slightly concerned about that flashing. You mention that the roofing membrane is correctly tucked up behind the flashing, but are you absolutely sure that it isn't damaged anywhere? I notice that the flashing doesn't overlap the roof tiles externally. Does it have a decent, undamaged horizontal overlap below the tiles, on to undamaged membrane?

5. The right-hand corner of the upstairs window sill looks a difficult flashing challenge. Are you sure that it's watertight? I can't see any drip groove in the underneath face of the sill, so it's possible that water run-off could be travelling back into that tight corner below the sill. Also, have you checked to see that the sealant around the window is in good condition?

As I said, there's a heck of a lot going on around that area, and you need to check every conceivable leakage source and water entry point.

 

[Feltwell]

Thanks everyone for all your thoughts, much appreciated.

So far, the list goes:-

Downpipe. I'm now sure this is OK - I ran a hosepipe into the guttering above for about half an hour today, all appears to be fine, no leaks or blockages anywhere and no evidence of water running down the outside of the pipe.

Overflow. This is still a possible - it does tilt upwards slightly. I checked the header tank and it's got lots of crud inside it so it's difficult to tell where the "tide mark" is. The water though was about an inch below the overflow. I thought I'd see what happened if it did overflow so I held the ballcock down, which revealed that the inlet valve is seized (another job found.... )- it only let out a few drips - so it's unlikely to have overflowed recently. I will run the radiators for a while and see if any water is returning to the tank when the system is hot. It won't be anything running down the outside of the pipe - the pipe run is stupidly long (at least 40 feet) and very twisty, the first part is exposed as well.

Roof joint. I don't think it's this - what you can't see from that picture is that there are lead soakers underneath each tile that extend up behind the flashing, so both they and the membrane would have had to have failed for this joint to leak. I stripped a section out yesterday and all was fine. Whilst it's not impossible for the membrane to be torn, it's unlikely as it's incredibly strong stuff (Proctor Roofshield if anyone's interested - much better than some of the cheaper membranes that the roofer showed me). The top centre point of the leak area is also a good 12" above the roofline.

Internal pipes. Definitely nothing from above - the ceiling in the kitchen has been replaced by a previous owner with foil-backed plasterboard, so apart from at the joints it would be impervious to water from above. I had the floorboards up yesterday and there was undisturbed dust covering the foil backing beneath every pipe joint and run in that area (including the overflow). The white pipes you can see in the picture are a possible if they are corroded within the wall - they are heating pipes - I may end up cutting them out to check, I was thinking of moving them anyway.

Window above. There is no drip stop on the cill, and the seal around the window is poor - but would that be enough to cause this much damp? The other point against it is that it's to one side of the damp area, and the wall directly beneath the window is dry both internally and externally.

I am still wondering if this is just the after-effects of my storm flooding 2 years ago, where the water definitely came right into this exact area. It does seem a long time for the effects to appear though.

I guess I may end up just leaving this for a while and observing it to see what happens. How long do you reckon I need to leave for it to dry before I lime plaster, presuming no more leaks? I was thinking about 3 months?

 

[Jon Maine]

Under normal conditions it is suggested an inch of wall thickness a month to dry thoroughly so this is probably not a 2 year old hangover.

The damp patch does seem to follow the downpipe, could the water in some conditions be missing the guttering and flowing down the outside of the pipe instead?

 

[Schoolmarm]

I don't think it is your old storm damage.


If you thought your leak was totally cured then lime plastering would not be done onto a dry surfaceanyway.


"Window above. There is no drip stop on the cill, and the seal around the window is poor - but would that be enough to cause this much damp? The other point against it is that it's to one side of the damp area, and the wall directly beneath the window is dry both internally and externally."

It does do some amazing travelling sideways and down though.

 

[Matt Green]

Downpipe. I'm now sure this is OK - I ran a hosepipe into the guttering above for about half an hour today, all appears to be fine, no leaks or blockages anywhere and no evidence of water running down the outside of the pipe.

Could you try blocking the outlet and trying that again? A heavy deluge and a partial blockage might cause it to overflow at that joint. It would be interesting to see what happened nonetheless.


Matt

 

[Feltwell]

Thanks everyone again!

Matt, yes I'll try that next weekend. I think it will just back up to the joint above the shoe and then leak out, gradually backing further up the pipe - the joints aren't sealed (which I understand is correct), although they have got a few years of muck and paint around them.

The gutter above stops pretty much directly above the problem area. It serves a lot of roof - a picture of the back of the house is below - and I've always thought it looked under-sized. However, because of that slight paranoia I have been outside under an umbrella in several severe downpours to check what is happening, and it doesn't ever seem to over-top the guttering.

I really wish this was just an internal pipe leak - it would so much easier to fix! One thing that keeps nagging at me is that the weather lately has been quite dry, we've been here through some very wet times (lots of flooding round here about a year ago) with no problems other than 1" of water in the cellar one time. If it was a "design fault", such as inadequate guttering or a failure in the design of the roof joint or the lack of a cill drip groove, I would have expected it to show up before now.

I take the point on water being able to travel. One further thing I can do is to get into the roof space of the single storey part. There's no access at the moment, I've been meaning to put a loft hatch in for a while. If I do this now I can check the "outer" surface of that wall below the roofline.

 

[Jon Maine]

That's a picture that says it all I think, just imagine if the down pipe were not there in that picture, what can you see?
What does it line up with?

I think it looks quite obvious.

 

[Schoolmarm]

What ? the valley?

 

[Jon Maine]

Max area of roof 53m2 115mm gutter 65mm outlet
Max area of roof 65m2 125mm gutter 75mm outlet
Max area of roof 103m2 150mm gutter 89mm outlet

A quick estimate makes me think you are not far away from the 65m2 for that elevation.

n.b. the area must be calculated on the entire surface area on the slope not plan, If you want to calculate from plan x 1.4 for a 45 degree pitch

 

[Jon Maine]

What ? the valley?

Yes, the whole area above the rear valley will be gushing out over that gutter I am sure which is why the black staining is down the wall.

Best monitored in a heavy rain storm to confirm but looks like it to me. Strangely that is something we dont often do when we should check the gutters when it is really p***ing down.

 

[Feltwell]

I think the black staining is old Jon. The valley does indeed channel water to that point, but I have been out in the p***ing rain to check several times and it doesn't overflow the gutter, though I'd bet it comes close. The wall does appear to be dry behind the downpipe, inside & out, apart from the problem section at the bottom.

The downpipe isn't in the original place - you can see the marks where pipe nails have been in the past, it was originally a few inches to the right. Given the level of maintenance given to the rest of the house over the years (let's be polite and call it "minimal") I bet it was leaking for some time before it was fixed, hence the staining.

 

[Jon Maine]

I think the black staining is old Jon. The valley does indeed channel water to that point, but I have been out in the p***ing rain to check several times and it doesn't overflow the gutter, though I'd bet it comes close. The wall does appear to be dry behind the downpipe, inside & out, apart from the problem section at the bottom.

The downpipe isn't in the original place - you can see the marks where pipe nails have been in the past, it was originally a few inches to the right. Given the level of maintenance given to the rest of the house over the years (let's be polite and call it "minimal") I bet it was leaking for some time before it was fixed, hence the staining.

A little problem with my gutter and downpipes cause a similar but heavier staining.


I do use a mastic on cast iron downpipe joints.

It is difficult to tell without being there when it is raining heavily, although I do suspect the gutter outlet and down pipe will be stretched in a heavy rain storm.

 

[Matt Green]

I'm with Jon, that valley looks like it's overshooting the gutter and/or the downpipe is undersized.


Matt