Water on inside of roof in loft

Soldato
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I’m not in the loft very often but when I was getting the Christmas decorations down everything felt damp and there was a strong foisty smell. I spoke to a roofer I’ve used before and he came out and had a look inside and out and said he couldn’t spot any issues and that it was most likely condensation. However when I’ve been up again yesterday there was water drips over all of the things in the loft and visible water on the felt and also white mould. The smell also seems worse.

I assume this isn’t just condensation as I asked my dad to check his loft and he said there is not water or mould on the inner felt.

what could be the cause of this? Any ideas?
I’ve used the roofer before and I’ve always thought he was spot on but perhaps not (unless he’s just missed something of course).

I had the soffits and guttering done a couple of years ago. Could it have been done wrong? Not sure if that would result in water droplets on the felt though?

Thanks.
 
Soldato
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Dorset
I get the same, so am interested to hear people's thoughts on this.

My loft is ventilated all the way round, but I occasionally get water droplets up there.
 
Associate
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Up North
I’m not in the loft very often but when I was getting the Christmas decorations down everything felt damp and there was a strong foisty smell. I spoke to a roofer I’ve used before and he came out and had a look inside and out and said he couldn’t spot any issues and that it was most likely condensation. However when I’ve been up again yesterday there was water drips over all of the things in the loft and visible water on the felt and also white mould. The smell also seems worse.

I assume this isn’t just condensation as I asked my dad to check his loft and he said there is not water or mould on the inner felt.

what could be the cause of this? Any ideas?
I’ve used the roofer before and I’ve always thought he was spot on but perhaps not (unless he’s just missed something of course).

I had the soffits and guttering done a couple of years ago. Could it have been done wrong? Not sure if that would result in water droplets on the felt though?

Thanks.

It's probably condensation, been very cold outside the last few days.

You say you had the soffits replaced - is there any ventilation?

Generally you want a decent draught blowing through the roof space to remove the moist air before it can condense on the cold surfaces (i.e. underside of the roofing felt).

So that may be your issue - lack of ventilation perhaps.

You could get some ventilation added if this is the issue - either on the underside of the soffits via the circular grills, but you need a load (about one every 200mm to get the equivalent of a 10mm wide gap across the full width of the house). You can also get over fascia ventilators that are a lot more discrete but you'd need to have the bottom row of tiles stripped back to fit these.

Another option are ventilated tiles - but would mean replacing some tiles to fit these, but I'm not great a fan of these due to the chance of roof leaks if installed incorrectly.

Finally, there is also the option of vent trays that fit between the rafters (they slide over and under the felt), and allow air into the roof through gaps where the tiles overlap.
 
Soldato
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12,414
Might be worth looking around the edges of the inside of the loft and pull back any insulation from the eaves that's blocking air flow and thinking about anything that could be causing warm air and moisture entering the loft from the house
 
Tea Drinker
Don
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It’s on the felt only because that’s the dew point or coldest bit. Things to check

Going to assume you have a cold roof that the insulation is on the ceiling not under the tiles

Do you have bathroom extract running through that’s leaking damp air
Do you have a bathroom extract that’s only extracting to the loft not outside
If it’s insulated has the insulation been pushed right up to the tiles and felt. There should be a cross flow it’s a common problem people insulating right up to the felt
Do you have soffit ventilation if not you should
 
Soldato
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5,452
I noticed this in my loft just yesterday and I'd been up there a week previous and not spotted anything.

I think judging by the pattern of water droplets, moist air was creeping past the loft hatch (even though it's got a seal around it) probably due to drying clothes in a room upstairs and leaving the bathroom door open before all the steam had cleared.

I think ordinarily with milder temperatures it wouldn't have a chance to condense in the loft, but when it's effectively freezing up there as it is now it's not surprising.

I've bought some of those roof felt lap vents anyway to encourage more of a draught even though the soffits are vented.
 
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Associate
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Stafford
Yes I predict this is probably snow on the roof. Normally the snow would not be there and although the roof would be colder than the loft space the ventilation trough that space would allow the air to blow out before it can condense but if the roof is particularly cold I.e covered in snow then it possible it could happen.
 
Soldato
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When I had my loft insulated they used triangles of white polystyrene instead of those vents. They looked pre made.

Not long after we moved here I put a double brick vent in each gable end so through flow ventilation
 
Associate
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If ventilation is all ok, look for where moist air could be getting in - the light fittings in the bathroom could be letting steam past for example, & you don't need much.

Fit felt lap vents if you don't have any - they're really cheap & just space the underfelt between layers.
 
Soldato
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I had a condensation issue this year as the cold weather set in too. I did 3 things and it’s solved now:

Pulled back the insulation a little, there was gap between the insulation and the felt but I made it a little bigger (soffits are vented).

Replaced the seal around the loft hatch.

Installed a load of lap vents (almost one in every ‘gap’ down both sides, staggered at various heights).

Seems to be fine now.


Exactly these, they just slot in and create a lot more ventilation.
 
Soldato
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We had a similar issue, a roofer came round and advised to put vent tiles in, he put in four - two high and two low, the issue went straight away.
 
Soldato
OP
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Newcastle upon Tyne
Thanks for all the info and advice. Ive ordered some of the felt laps to try as the reviews are great and its an cheap fix/improvement.

It’s on the felt only because that’s the dew point or coldest bit. Things to check

Going to assume you have a cold roof that the insulation is on the ceiling not under the tiles

Do you have bathroom extract running through that’s leaking damp air
Do you have a bathroom extract that’s only extracting to the loft not outside
If it’s insulated has the insulation been pushed right up to the tiles and felt. There should be a cross flow it’s a common problem people insulating right up to the felt
Do you have soffit ventilation if not you should


There is a bathroom extractor but all seems to be venting correctly outside and the insulation doesn't seem to be touching the tiles but I've pulled it away a little further.

There are no visible soffit vents (eg the round little discs, should there be?
 
Tea Drinker
Don
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Sunny Sussex
Discs or linear vents yes. If there's none that'll be your problem. Cold roofs need cross flow ventilation or they condensate. Retrofitting will be painful try the felt vents or tile vents first.
 
Associate
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UK
Just noticed the same issue here with some falling/running damp now along side of rafters, with the felt vents is it fairly "diy-safe" to separate the felt at join lines and put them in? Or are they easy to rip and turn into a $$$$ problem?

Not obvious where mine is coming from, loft hatch isn't sealed so maybe just hot air rising while it's -2 outside.
 
Soldato
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They are very DIYable. If the felt is stuck together, peel it away carefully with a blunt butter knife but as you say, don't rip it. I didn't have any problems but my roof isn't that old.

I did 25 in under 10 mins which included crawling though to an area which isn't boarded in my 'L' shaped roof.
 
Soldato
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Quite a few reports of this popping up on Facebook as well, cold temps and little wind is exacerbating it.
 
Associate
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Yeah I've been up in my loft this week and also noticed this. Hoping its just the weather and time of year but noticed at the same time that my in line extractor which was fitted just over a year ago has been leaking condensate and had probably about half a litre of water sitting in the ducting. Can't imagine that will have been helping. Rigid ducting purchased and will be installing it myself over the next few days. At least then I know it will be done right! Hopefully that will sort it out, might wack a few of those felt vents in as well though.
 
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