31 May 2021
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United Kingdom
Hi there

First time using this forum so many thanks in advance for any help anyone can provide, it's very much appreciated! I'm in England - cold winters, warm summers.

I have a new shed (installed December) which, for the last two days, has dripped onto the floor from the ceiling for five minutes, then stopped, and then dried up within the hour. It's happened the last two days in a row, oddly the same time late afternoon. It can't be rain related as it hasn't rained for the last seven days and it's been 22c/72f outside for the last few days. The temperature inside the shed is 25c/77f. The shed never leaked in heavy rain, so I assume this must be condensation. The shed is very well sealed, shiplap cladding, breather membrane, 50mm insulation board/foil tape, vapour barrier (all edges/corners completely sealed with sealant adhesive - floor, walls, ceiling), then OSB board.

It's a sloping pent roof and it drips about halfway down at the crossbeam supporting the roof. As I said the shed is well sealed and the next thing on my list is ventilation which I haven't gotten around to yet, new baby and all. Yesterday and today, I had the double doors open and an oscillating fan running all day, and it still dripped. The fan also runs at night every few hours for an hour at a time.

Has anyone experienced this and have an inkling what could be causing it, and more importantly, how to stop it!

As I said at the top, many thanks in advance for any support you can provide.

Thank you.

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Roughly how much water drips? An eggcup, a tea cup, A mug?
Does the shed have any pipework running through the rafters?
Thanks for responding Conny.

We’re talking just an egg cup, there is no pipework in the shed.


Can you see exactly where it is coming from in the roof? There may be a 'pocket' between the insulation which is causing condensation to pool and then 'overflow'. I'm simply guessing to be honest.
Strange it happens around the same time each day.
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my thoughts

what is the floor construction
is the ceiling treated with say gloss paint [stopping breathing ]
if you tape or pin plastic to the area which side is affected ??
Is it located near any overflow or other plumbing pipework?
Thanks for all the replies. Here is an image showing the material make-up of the area in question -
6bV8pkN, also some annotated photos -

Conny - I can see where it is dripping from, it could be pooling condensation above the insulation board which then reaches the edge of the board and drips, but could that get past the vapour barrier adhesive sealed to the joist? I wonder if the temperature affects it, as it's been the same temp outside both days, and 3pm is the temperature point where the moisture converts. I'm not into chemistry so just guessing. It is wet under the foil tape which suggests it's above the vapour barrier.

Big-all, thanks for replying - The floor is 100mm concrete base, thick poly DPC, shed wooden floor beams onto DPC, 25mm timber floor, my own thick poly DPC inside onto the floor, DPC is sealed with adhesive sealant and foil-taped to foil-backed insulation boards six inches up the four walls, vapour barrier on all walls is sealed to the DPC using sealant adhesive all four walls, 25mm floating insulation boards onto floor DPC, then floating floor 22mm water-resistant chipboard. The floor is not penetrated by any fixings to ensure no holes. The OSB ceiling is painted with a matt white paint. I'll try taping some vapour barrier to the ceiling to see what happens regarding condensation.

CBW, thanks for replying - There is no plumbing pipework in the shed at all.

Thanks all.


Photo links here:
Material make-up -
Three annotated photos -
so all inside surfaced are wood ??
normal causes off condensation
things like gas or parafin heating give out massive amounts off water as do tumble drying without venting outside
if you pin the plastic to the roof where the problem if it gets wet on top the moisture is coming down from above or underneath from the shed
what are the contents off the shed they may have absorbed a lot off damp over winter and now being driven out by the heat ??
You need to seal around the edges and joints in the PIR board to prevent moisture laden air condensing on the cold roof surface above.
Either foam sealant from a proper gun (~£20), don't bother with the aerosol cans, you will spend more time cleaning up the mess as they are nowhere near as controllable as a decent gun.

Or foil tape across all joints, or both...
Big-all - Yes all inside surfaces are wood. The shed doesn't have anything in it that creates moisture. I'll do what you suggest with the plastic in the next day or two, and see what happens. The shed has items in it that were previously in the house, so they won't have been damp. The shed was installed in December, and I fitted out the interior as described above between January and March in snow and rain. The items in the shed were transferred in March and I have had an oil-filled radiator coming on periodically so that it never goes below 12c at night. Since last week, now that it's sunny I've switched over to the oscillating fan to create air movement. Maybe it will settle down in the coming months.

Raykf, thanks for replying - All edges and joints of the PIR board are sealed with foil tape, I then have a poly vapour barrier onto the PIR board, adhesive sealant sealed and foil taped at all edges and corners, floor, walls, ceiling.

It's stumped me for sure!

Many thanks.

Thanks for replying Jowwy.

I was about to start on ventilation, but a new baby decided to change that. I’m thinking of screened vents at the front and the back when I get some time. The double doors had been open all day on both days that it dripped last week, so I was puzzled, but maybe it’s a build-up from the last few months, where it’s not been ventilated and is well sealed. I have an oscillating fan running every few hours, I’m hopeful when the ventilation goes in, the issue will go away.

Thank you.


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