Water Drops Condensing on Loft Felt - Need to be Concerned?

[n-hatton]

Hi All.


Just looking for reassurance!

Thought I'd nip in the loft and check all pipe work's lagged ok - given extreme weather! Noticed I have water condensating in droplets on underside of roofing felt and occasionally dripping down! I'm in the south and we've had NO snow here - so not blow in and thawing etc.

House is 18-years old, loft was insulated to the tops of the joists. 2-years ago I laid a second layer across the top - new minimum? I kept all insulation back and away from the sofit ventilation. Loft is now always hotter in summer and colder in winter - suppose this means all's working well? Yes, I did box in the water tanks and increased their insulation as well - making sure no loft insulation is beneath them.

Never had this condensation before! All timbers are dry and never been any sign of them being damp - not even now. Assume this maybe normal and is warm air rising and condensing on the underside of the cold felt? Have noticed I didn't add any insulation to minimal amount on the loft hatch or do anything to it 2-years ago. Could warm air be passing up via it and be the cause?

Any need to be concerned?



Cheers,
Neil

 

[RigidRaider]

Have you got any halogen downlighters in the ceiling? Moisture will be rising through them.

TBH I wouldn't worry if the condensation disappears when the weather warms up. These are extreme conditions.

 

[n-hatton]

Rigid.


No, we have no low-voltage or recessed lights in bedrooms. Also, bath and en-suite have extractors.

Sounds as if it is just extreme weather, though loft hatch - I now realise - isn't up to the standard I did elsewhere when insulating the loft. DOH!


Cheers,
Neil

 

[ajrobb]

The relative humidity outside hasn't dropped below 90% for days now. Roof tile temperatures can drop below air temperature at night, so it might be dew. When did you observe the condensation? If it was in the morning, check again mid afternoon when the sun has had a chance to warm up the loft a bit.

I worry that the levels of loft insulation the government are pushing to drop CO2 emissions might be excessive. Without a vapour barrier on the warm side of the ceiling, the loft space needs to maintain a relative humidity well below 100% so that moisture escaping through the ceiling and water evaporating from the cold tank can be diluted before it condenses. When the ambient air is at 100% and there is practically no heat getting into the loft, how is that supposed to happen?

Do you have a vapour barrier lining the cold tank enclosure insulation?

The extractors don't vent into the loft do they?

 

[RigidRaider]

Surely with a snug fitting lid on the tank and approved light fittings in bathrooms there shouldn't be excessive vapour getting into the attic? I guess cooking and clothes drying will create vapour though....

We have an Aga, cooking takes place mostly inside the ovens so moisture goes up the flue. We also have a multi-fuel stove so the living room is very well ventilated.

 

[n-hatton]

Ajrobb.


I think I understand what you're saying.

Noticed condensation about mid-day today. Just been up again (16:30); still at same level - but been no sun at all today and only got colder! In fact frost stat turned heating on this afternoon!

The extractors have flexi ducting and vents set in the roof tiles - they don't vent into the loft itself.

There is no vapour barrier around water tank. It has it's lid fixed on correctly and a standard black jacket. When I added the extra insulation 2-years ago, I also built a flimsy wooden frame around the tank, then fixed sheets of polystyrene to it - about 40mm thick - on all sides and top. The sheeting is applied double thick - so 80mm. Looks like a large polystrene cube in my loft.

The extra insulation I added 2-years ago was the stuff inside the silver and orange coloured plastic lining - mentioned having to go silver side up? I laid this over the standard "open" fibre glass stuff that already exisited. There's no vapour barrier to the ceiling's plasterboard.

Getting a bit worried now. Odd never seen it before and last year was very cold - with snow! Had snow blown backwards into one of the extractor ducts then - thawed and dripped out via the ensuite ceiling extractor fan! Went into the loft space; didn't notice it then.

Will have to cover and seal the loft hatch - to prove that. Is off set from the stair case, so warm air coming up 2 floors. Am sure everything else is relatively tight - apart from sofit venting of course.


Cheers for any advice, Neil

 

[mointainwalker]

@Rigid

Bit surprised you are giving advice about this at same time as seeking it for very similar situation on other thread.

 

[mointainwalker]

@ OP

Condensation only happens when conditions are correct and the two elementr are low temperatures and high humiditry.

Even if your loft is cold, if you can prevent warm . moist air hitting that, then you will not get condensation.

The way to do this is to install a physical vapour barrier ( plastic-sheet) between the ceiling and the insulation.

 

[RigidRaider]

@Rigid

Bit surprised you are giving advice about this at same time as seeking it for very similar situation on other thread.

Yes, although my concern in asking the question was heat build up around the lamps. As the thread evolved it occurred to me that they might also be a route for moist air from bathrooms but then I realised that halogen lamps for bathrooms are made differently to prevent moist air from passing through. I've spent quite a bit of time in the attic recently installing my solar panel and then adding another layer of glass wool and I know ours is very well ventilated!

 

[n-hatton]

Hi All.


Thought I'd post back.

Just did a test. Last week applied draught excluder to loft hatch, taped some old pillows in plastic bags to the reverse of the hatch, closed it and applied masking taped over the gaps!

Removed all and checked this morning. All is as dry as a bone! No condensation on the felt underside.

Yes, snow has cleared from our bit of Berkshire for a couple of days - still pretty cold though. No sign at all of previous water dropping on stuff in the loft - all signs have evaporated! Hopefully indicates it only happened over this short period and extreme weather?

Will keep an eye on things - especially when snow returns.

Not sure about the mentioned\suggested vapour barrier? Think I understand that with extra loft insulation, there's less heat rising to take the chill off the felt and roof tiles that would encourage condensation? But wondered if there is less heat now rising through this route then isn't there in theory less moisture?

I think\hope the poor loft hatch was my problem and the extra insulation exaggerated it? Have now noted how some customers hatches appear to be securely fixed down and loads of effort spent with draught excluder after being topped up with insulation!


Cheers all,
Neil