Condensation and Humidity problem in loft

[n0166895]

Good evening all

I insulated my loft 2 years ago, from a warm loft to a cold loft. In the November after insulating I went into the loft and noticed all the timbers and felt was soaking wet, presumably through severe condensation. It was that bad mould had started to grow on all rafters.

I then went ahead and had 6 cent tiles added. A few months on I thought all the problems had stopped with the loft drying out. However this winter I went back up there and noticed some mildew, but though lt it may have been there from the previous year as I may have not cleaned it off properly.

So I decided to get myself a couple of hygrometers wireless ones and put them in my loft. I've noticed that my loft is constantly above 70% Relative Humidity. The last couple of days it has been constantly above 80%. I have put a dehumidifier up there which drops the humidity by a couple of % so it doesn't really do a lot.

What I have noticed is that when it rains, the humidity reaches about 85% where it levels off. I have checked for leaks and can't see any. Strangely even when it's cold there isn't too much condensation on the under side of tiles or felt.

I have had a couple of roofers have a look and they don't understand why humidity is so high. One suggested a new roof as the tiles may have become porous, but no one else on my road has this problem and they all have the original roofs.

When bathing and showering humidity doesn't seem to rise but over night it does a couple of percent.

Any suggestions anyone? My worry is rot in the loft, but I have read an article saying this is now common in a lot of well insulated lofts throughout winter but the lofts dry out of summer. However it has been mild today, 16 degrees and humidity is till 85%!!

Any ideas??

 

[Mr Chibs]

Not that it's science... but according to iPhone weather app, the humidity is 86% today anyway.

I've seen quite a few times, that there can be air leaking from downlight cut-outs into the loft, and I have seen bathroom extractor piping not sealed properly and these can aid moisture in the loft.

Is there any ventilation in your roof... at the ridge/eaves?

 

[n0166895]

Not that it's science... but according to iPhone weather app, the humidity is 86% today anyway.

I've seen quite a few times, that there can be air leaking from downlight cut-outs into the loft, and I have seen bathroom extractor piping not sealed properly and these can aid moisture in the loft.

Is there any ventilation in your roof... at the ridge/eaves?

There is little ventilation from the eaves that I can feel. Insulation is well away from the eaves so plenty of a gap it just as if the soffits were fit snug to brickwork.

Maybe some moisture may be getting up there from spotlights, but when showering and after the humidity doesn't seem to go up.

We have 6 tile vents but it doesn't feel very drafty up there.

 

[Murdochcat]

Have you put too much insulation near the eaves so that the loft can’t breath?

 

[freddiemercurystwin]

Ventilation is the key, you should be feeling a draught up there there should be some much ventilation, you need to check how/if your eaves are vented ....
You can stick timber wedges in the laps of the felt as an initial temporary solution or you can buy these: https://www.amazon.co.uk/Roofing-Stops-Condensation-Ventilation-Airflow/dp/B00M9ILJPG

 

[n0166895]

Have you put too much insulation near the eaves so that the loft can’t breath?

There's enough of a gap. Haven't stuffed the insulation into eaves and insulation not touching the felt or tiles anywhere.

 

[n0166895]

Ventilation is the key, you should be feeling a draught up there there should be some much ventilation, you need to check how/if your eaves are vented ....
You can stick timber wedges in the laps of the felt as an initial temporary solution or you can buy these: https://www.amazon.co.uk/Roofing-Stops-Condensation-Ventilation-Airflow/dp/B00M9ILJPG

Already bought these and installed but loft still seems quite still in terms of air movement. Don't get me wrong when it's really windy outside the loft humidity drops according to my hygrometer, but when it's not so breezy outside can't feel much air movement up there.

Is it normal for humidity to go up in loft if it's raining outside?

 

[freddiemercurystwin]

How many have you fitted?

 

[n0166895]

How many have you fitted?

About 15

 

[freddiemercurystwin]

Well however many you it's apparently not enough, there's no substitute for proper eaves vents IMO. That or too much moisture is getting into the loft from the floor below.

 

[n0166895]

Well however many you it's apparently not enough, there's no substitute for proper eaves vents IMO. That or too much moisture is getting into the loft from the floor below.

When you say eaves vents do you mean soffit vents?

 

[freddiemercurystwin]

Eaves can be vented through the soffits or under the tiles where they overhang the gutter but typically soffit vents will be easier to install as a retrofit the key to either is to make sure there is definitely a sufficient gap between the insulation and the underside of the felt.

 

[JP_]

More vents, and check for leaking extractor fans.

 

[JohnD]

CONDENSATION IN LOFT (ANSWERS)

This seems to be the time of year for condensation in lofts, so instead of replying to lots of queries I though I would write this "one-size-fits-all" post. Please also see //www.diynot.com/wiki/Building%3ACondensation-in-Houses Condensation in lofts occurs when the amount of water...

www.diynot.com

 

[Why Not Indeed]

Is it normal for humidity to go up in loft if it's raining outside?

The more breathable the loft, the closer the temperature and humidity will be to the outdoors.
The other thing is, the humidity reading you're looking at will be relative to temperature, so the reading will fluctuate with temperature, regardless even if there is no change in amount of water in the air.