Mystery Damp!

road2ruin

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Morning!

Hopefully look towards the hive mind of the GM forum for some ideas of a damp issue we're having in our loft which so far no one can get to the bottom of!

A few weeks ago I noticed a patch of damp on one of the boards in our loft (fully boarded) and thought it was something I should keep an eye on. I noticed that it seemed to be getting slightly worse and was definitely damp to the touch. There was no obvious damp areas in the roof and during one of the recent, heavy downpours I was up there for a good 30 minutes watching for a drip and nothing was forthcoming. We also had an electrician in to swap out the lighting and he had his steps and also had a look at the roof and said it was also dry. Just in case we got a friendly roofer out to come and have a look, they got onto the roof and also into the loft and confirmed that a visual inspection didn't appear to show anything obvious.

If it wasn't coming from above then it would make sense that it was probably below especially as it had got worse since we had put the central heating on although the odd thing was that there was no sign of any water coming through the ceiling. Got a circular saw out and effectively cut the damp patch out expecting to see pipe work underneath but nothing bar insulation which was bone dry. The back of the board was also completely dry so it wasn't something that was soaking through from below.

I can also confirm that there was nothing sat on top of that damp patch that might have leaked. I have had a large piece of my daughters drawing paper covering the hole for the last week and having checked last night there are zero spots of water on it which seems to confirm that there is nothing coming from above.

So essentially, got a damp patch but absolutely no sign of where the dampness might be coming from. Any further things that I might be able to investigate as being the cause?!
 

RichA

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What's directly above? Maybe a drip from condensation, originating from whatever central heating components are in the loft - therefore happening at times when you wouldn't think to be looking for moisture.
 

road2ruin

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What's directly above? Maybe a drip from condensation, originating from whatever central heating components are in the loft - therefore happening at times when you wouldn't think to be looking for moisture.

Nothing above bar the roof itself, no pipework or beams that moisture should be dripping from. We’ve also had that paper up for a week which doesn’t show any drips coming from above which I hadn’t expected.
 

RichA

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Weird. Can only think that maybe that's a cool spot that's causing moisture in the air to condense on it.
Do any bathroom extractor ducts run though the loft space? If there's a hole in the ducting it could be chucking steam into the loft.
 

road2ruin

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Weird. Can only think that maybe that's a cool spot that's causing moisture in the air to condense on it.
Do any bathroom extractor ducts run though the loft space? If there's a hole in the ducting it could be chucking steam into the loft.

They do however they are around the end of the loft towards the eves and this is right in the middle!
 

road2ruin

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Has there been anyone working in the loft that could've spilled something, or maybe a cat a rat or a squirrel.

No although this was the question asked (spilling/leaking) by the roofers and the electrician. There’s definitely not been anyone in the loft bar myself.

It’s odd as the damp patch does look like something wet has been sitting on top of it. It almost has the look of a white ‘tide mark’ outlining parts of it?!
 

williamalex1

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No although this was the question asked (spilling/leaking) by the roofers and the electrician. There’s definitely not been anyone in the loft bar myself.

It’s odd as the damp patch does look like something wet has been sitting on top of it. It almost has the look of a white ‘tide mark’ outlining parts of it?!
Was the damp showing on the underside of the board you cut out?
 

clubchamp98

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Wind has blown rain under the tiles of the roof in my last house .
took me months to work it out as it wasn’t directly over the patch.
The rain water ran down the lining under the tiles.

Brown paper over the mark and check daily the wind direction.
 

SocketRocket

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Wind has blown rain under the tiles of the roof in my last house .
took me months to work it out as it wasn’t directly over the patch.
The rain water ran down the lining under the tiles.

Brown paper over the mark and check daily the wind direction.
That could be it. I had a similar experience during a particularly heavy storm, the combination of unusually heavy winds and rain had allowed water to blow under some flashing and drop down onto the ceiling. It didn't reoccur again.
 

clubchamp98

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This is exactly what I've done, I've had a roll of paper over it for 5 days now and so far it's completely dry.
Just keep checking when you get some high winds.

Having said that tracking it down is another story.
But at least you will know.

I used a boot liner off my old car with some foam in it to stop splashes so the water didn’t get into the floor boards
 

Rlburnside

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That could be it. I had a similar experience during a particularly heavy storm, the combination of unusually heavy winds and rain had allowed water to blow under some flashing and drop down onto the ceiling. It didn't reoccur again.

Similar to me too, had 2 damp patches in loft, no sign of it coming in so went outside and looked on roof still no sign of anything untoward.

Just had a re-roof and after roofer took tiles off the felt was damp caused by high wind and rain getting under flashing.
 

SocketRocket

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Similar to me too, had 2 damp patches in loft, no sign of it coming in so went outside and looked on roof still no sign of anything untoward.

Just had a re-roof and after roofer took tiles off the felt was damp caused by high wind and rain getting under flashing.
Ours only happened during the 'Beast from the East' Storm where the high winds and rain were from the East as to the normal South Westerly direction. It hasn't happened again.
 

Oddsocks

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If all of your rads are on the outside walls of the house, what’s this chances that it’s pushing the cool air to the middle of the loft and condensing?

It’s a long shot but in our old house we noticed damp in “ cold corners “ where the rads were not connecting. It’s merely me clutching if warm air is raising as the temp drops quick at night could it potentially cause a cold spot in the middle.
 
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