Condensation in loft

[jocojohn]

Hi, my son recently bought a 3 bedroom semi detached house which is only about 3 years old. The surveyor noticed a small amount of condensation in the loft and suggested the loft floor boards are removed ( only about one third of the loft is boarded )
Recently my son noticed the condensation is a lot worse with moisture dripping from the roof felt material.
He contacted the NHBC but they have been less than helpful, just sending him a leaflet about condensation. he is now contacting them again to get some practical help in sorting this out.

could someone on here please help with the following?;

1) Can boarding out a loft cause condensation?
2) Can a loft have too much ventilation. ( daylight can be seen along almost the whole length of one of the eaves.
3) Should bathroom extractor fans be vented directly outside, one of my sons 2 bathrooms is vented through the loft although my son is not using this fan now and the vent is closed when not in use.

PS There is a good amount of loft insulation, a depth of about I foot.

Thank you for any advice you may be able to offer.

John

 

[stem]

Can boarding out a loft cause condensation?

No. Warm, most air touching a cold surface causes condensation.

Can a loft have too much ventilation

Not really, the more ventilation the better, building regulations over the last 20 years or so have increased the ventilation of lofts, to combat condensation.

Should bathroom extractor fans be vented directly outside

Yes they should. It's OK for the sealed duct to pass through the loft but the moist air from the the bathroom must be vented outside and be directed away from any aforementioned vents that would allow it back into the loft space. I would be concerned if there was a fan exiting into the loft even if it isn't used. They are not airtight. If this is the case this may well cause condensation, it certainly won't help.

Are there any water storage tanks in the loft? if so do they have good lids. Sometimes, even though they are primarily cold water storage tanks under certain conditions they can get warm and cause condensation.

Is the loft being used for anything IE hobbies or to use exercise equipment?

Anywhere else warm most air can enter?

 

[KenGMac]

jocojohn, hi.

Suggest you have a look on "floors Stairs and lofts section" on the board.

There is a section dedicated to loft condensation.

You posted,
daylight can be seen along almost the whole length of one of the eaves.

Does this indicate that there is no daylight showing on the other eaves? if so, then air flow across the loft will have been stopped by the lack of cross venting.?


With the depth of insulation you note, about a foot, it is absolutely imperative that all eaves are vented and you must be able to see daylight along all eaves.

Question? has someone recently installed more insulation in the loft space? there are some right Cowboys in the Insulation game

Ken

 

[jocojohn]

Hi again,
Thanks for the replies,
I dont think I explained fully, the bathroom do not vent air into the loft directly but via a pipe/plastic ducting, and then through loft and out of roof, I just thought maybe the warm pipe in a cold loft might cause the condensation.

There are no water tanks in the loft.

It is not used for anything except storage.

As far as I can remember I can only see daylight one side of the loft but it may well be vented the other side as well.

Another reason I mentioned boarding the loft is that I have just bought a bungalow and I also want to board it out for storage. It also has deep insulation so to place boards on top would mean compressing the insulation to about half its depth.

Thanks again, John

 

[JohnD]

Are there any holes in the ceiling, for example downlights poked through?

Does anyone drape wet washing around the house or over radiators?

 

[jocojohn]

No, nothing different from his previous house and no problems there.

John

 

[Newboy]

to place boards on top would mean compressing the insulation to about half its depth.

Don't compress the insulation - raise the flooring!

 

[JohnD]

No, nothing different from his previous house and no problems there.

Except that a new house is likely to be better draughtproofed than an old one, and to have tight-sealed doors and windows, so less "accidental" ventilation.

If there is a water meter, have a look to check that the bubble stops turning when all taps are off, in case there is a plumbing leak. Water vapour is lighter than air so it will naturally rise through the house.

bathroom do not vent air into the loft directly but via a pipe/plastic ducting, and then through loft and out of roof,

I suppose it is possible that the duct might be badly-jointed and leaking steam into the loft. If so it might be visible on a frosty night, or you will smell it if you can persuade some stinking smoker to puff away in the bathroom.

 

[jeds]

I've designed and built dozens of houses and never had this problem until a period around December/February last year. It was a house I designed but wasn't involved in the build. The house was finished in about October 2013. To be honest I didn't really pinpoint the problem exactly but I suspect it was a cheap quality breather membrane, which probably wasn't helped by the extreme rainfall that winter. (remember that?) The membrane used didn't have any markings and the builder couldn't (or wouldn't) tell me exactly what it was or where it came from. In my research I was surprised at the difference in water vapour resistance between good quality membranes and the cheapest ones. Anyhow, I suggested fitting eaves vents, which the builder did, and the problem disappeared within a matter of a few weeks.

 

[theprinceofdarkness]

That sounds possible. it could be an idea to push in 6" length of hose pipe in the over laps in the breather membrane, to open up the joints a bit to allow a bit more of a draught.
Could be badly fitted ceiling roses allowing too much air through. So have you eave ventilators? Spec is one every 4' around the eaves. Are they blocked with insulation? Does your loft trap have an airtight fit? (and is insulated?)
Frank

 

[jocojohn]

Hi, thanks again for the replies,

My son is using the house exactly as his previous house and he had no problems there. Strangely though my son rang me yesterday and said the loft is now dry.

I will keep you posted if the problem returns, cheers everyone

John