Condensation in Loft

[doriclad]

Over the past couple of weeks I have had condensation in my loft which I have put down to the cold spell. The house is a new build approx 5 years old and is fully insulated at the ceiling. I can see down into the eaves so believe that the ventilation in the eaves is ok. However, due to the weather there hasn't been any wind/air movement to ventilate the loft and dry it out.

The timber trusses are quite wet in some places and so is the black underlay. Drips form on the black underlay and fall on to the insulation making it wet. I'm confident the insulation will dry out but concerned about the timbers.

I have been tring to identify the problem and I think that it could have stemmed from 3 spotlights I put in the ensuite. I put them in some time ago but didn't cover behind them leaving what I believe was a weak point where warm / moist air from the shower could rise into the loft above. I believe that the condensation I am seeing is a result of this. About 2-3 weeks ago I covered the lights with 200mm deep insulation to prevent any more air / heat rising through but the damage was potentially done. The hatch is well insulated/sealed and we rarely use the bathroom but even so there are no gaps, lights, etc that would allow warm air through.

I have someone coming to look at it next week but with the cold weather / still air it just isn't drying out. I have tried to dry with a towel but more water appears to form and drip from the black underlay. Its almost like the water is coming through form the outside but I can't see any damage to the tiles and its been frosty. Although the underlay is only a thin layer I am thinking that it has become saturated over time from condensation and that what I am experienceing is the water seeping out.

Can anyone let me know if they would concur with my thoughts?

I am also desperate to dry out the loft space so that I can get it back to normal and montior its condition. Drying the surface of the underlay with a towel is a laborious process and doesn't seem to be having a quick effect.

I was thinking of hiring a dehumidifier over the weekend now that the temp has risen to approx 7C. Does anyone know if this would have a worthwhile effect.

Alternatively, should I try and heat the space with an electric heater or open the hatch to heat / dry out the loft space then close once dry? Possibly cooling the house and loft (i.e. turning of heating / opening windows) after drying to cool the air in the loft again to outside temps.

Or should I just wait until the weather / wind picks up and not worry too much.

I just don't want to cause any long term damage to the timbers.

Help and advice would be greatly appreciated.

 

[doriclad]

Hi Onecall.

Got your message.

I just want to know if my thoughts on the cause of the problem appear logical to others or whether someone thinks it could be another cause.

Could the underlay become saturated / hold a lot of water from condensation?

I'd also like help / advice on how to dry the loft out i.e.
1. Dehumidifier.
2. Heat - electric heater or open hatch.
3. Do nothing i.e. just wait for weather to improve.

 

[datarebal]

you mention black underlay, this could be a bitumen based 1f (even if only 5 years old) this is not beathable. look to see if it is slightly sand faced, and has a reinforced backing.. you could try slightly opening the felt laps with small packers there by allowing additional ventilation into the loft.
you could add vent tiles or a vent ridge system. Personally i'd try the felt lap trick first as it's free and easy.
I should add, I believe you should be carefull covering the spot lamps .. there may b a fire risk ,but am sure someone else while confirm or deny this.

 

[foxhole]

Ventilation is needed and insulation to any pipework in the loft, do you have conventional boiler, overflow pipe should be lagged as it's often warm and provides constant source of condensation.

 

[alittlerespect]

Hi

You have 2 problems!

1. Lack of Ventilation to the roof void; If the ventilation is ok you should be feeling a draft, if not, it is likely that the soffit/ridge vents have been blocked possibly with insulation material, or you may need to add some ventilation.

2nd problem and possibly more realistic cause:Vapour Diffusivity;The fibreglass insulation material you are using has relatively good thermal resistance but has crap vapour resistivity. Solution: Take up insulation material and lay vapour barrier across ceiling and drape over ceiling joist, and relay insulation material (don't forget to where a face mask) this will keep the moist air on the warm side of the building and you should get a lot less condensation in the loft!

One question: did you not have the problem last year during the cold spell? If not, then it may be that the light fitting are contributing to the effects.

Regards

I wouldn't worry about the sarking felt at this time, the loft space should be quite cold this time of year (hardly above the outside temperature) as little heat is escaping through the insulation, it is this that makes the condensation problem more acute.

 

[doriclad]

Thanks for the replies.

I think that the vapour transmission might be the problem. I didn't really consider that the mineral insulation would still allow vapour to pass through. I've deceided to use the bathroom this week so not to create any vapour in the ensuite where the downlights are installed. I am also refraining from using the lights so not to generate any heat in the loft. I'll monitor the loft and see if there is improvement.

Hopefully, this will confirm the problem and I will looks to purchase downlight covers that are heat and vapour resistant - http://www.tlc-direct.co.uk/Products/TLALC724.html

Thinking about it over the weekend the ensuite is a smallish room and a lot of steam/heat is generated from the shower. I have a sealed downlight over the shower but 2 normal spotlights over the basin and toilet. The sealed one might be doing a bit of a job but the other 2 probably aren't.

I checked the eaves and there is a gap - I could also see daylight. So hopefully ventilation is ok. If I can eliminate the problem first then it will save the cost of installing vent tiles.