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Loft ventilation

(5 Posts)
Luuby86 Sun 01-Dec-19 23:32:46

So we've just noticed condensation in our loft this week. We've never had it before, and nothing has changed in terms of insulation amounts, or living habits from the previous 10 years we've lived here. (Eg extractor fans used in kitchen and bathroom, don't dry washing over radiators etc)

The insulation doesn't go up against the eaves, and there isn't a great deal of boxes stored up there (as we only have a tiny area actually borded and useable). We also have an insulated loft hatch.

The house is a 1900s mid terrace with a bitumen style felt under the slates. When I went up this week I noticed the felt was dripping, pretty much across the whole loft space.

Now I'm aware this is a ventilation issue (although slightly perplexed as to why it has become an issue now and not in the previous 10 years!) My plan is to have a crawl along the joists into the eaves and check the sofit vents are clear, but I was wondering if anybody has experience of the LapVent/EasyVent systems that you fit between the felt? They seem like quite a simple idea...can they really help that much?

I do also plan to have my roofer uncle go up and check the roof and see whether it's worth having ridge vents put in.

Also.....any clever ideas of how I can dry out the loft in the meantime? @PigletJohn any ideas?

TheSandman Sun 01-Dec-19 23:47:29

Extension cable and dehumidifier?

PigletJohn Sun 01-Dec-19 23:50:22

are there water tanks in the loft? do they have lids? are they warm?

do you have any ceiling holes for downlighters?

is the extractor blocked or leaking?

on a day when the heating is off, open the loft hatch and the back door. You should feel a strong draught going up the loft hatch. If the sun is shining, the felt on the sunny side should be quite warm.

look for any signs of rainwater or plumbing leaks. Look at the chimneystacks for damp.

clearing the eaves should be enough

as you are terraced, is the damp worse by your neighbour's wall?

Luuby86 Mon 02-Dec-19 00:14:06

Thanks for the reply @PigletJohn. To answer your questions:

No water tanks up there at all
No downlighters from there (the bathroom does have a downlighter but that's on a extension that is beyond the roof in question if that makes sense.... has its own flat roof)
Can't see any blocks or leaks from the extractors
Doesn't seem to be any worse towards either neighbouring walls.... In fact the walls themselves are quite dry.

Will do the loft/back door thing this week and see how it feels. I'm hoping it's just that the soffits might be blocked and that it's a simple remedy. Or that we get an almighty heatwave 😂

SurveyorScott Mon 02-Dec-19 08:25:47

Hi @Luuby86.

Having additional vents in the loft is never a bad thing, but, I doubt it would have helped much over the last few days.

We are in a period that surveyors refer to as 'condensation season' (Sept-April). This will affect any surface where the temperature is cold enough to drop below the dew point, the variable temperature at which water condenses.

However, temperature isn't the only factor. The last week has been exceptionally damp with external humidities at 99-100%, you probably noticed the mist and fog?

This means the external air cannot take any more moisture through evaporation, in fact, it's looking to condense it on any surface that it can.

The underside of the felt in your roof will be cold enough to be below dew point and that will mean condensation will form. Under normal, drier days, this will evaporate through good ventilation but in these really damp days it's hard to stop.

Interestingly you mentioned that the walls were dry, that's basically because they have enough mass to retain enough heat to stay above the dew point.

You said that it's not something you've seen often, which is good. You could check the top edges of the rafters for white marks or cracks (wood rot), holes (wood boring insect) and if you're worried contact a surveyor.

If you don't have any other symptoms then get some addition vents installed as it's always good, but try not to worry.

Condensation is often misunderstood by most builders etc. so just keep a eye on it over time before doing anything that will cost you £££.

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