condensation in the loft


Postby scott b » Thu Nov 18, 2010 9:43 pm

We suffer with bad condensation on our windows and plasterwork around them. I have just been in the loft and found that the roof is covered in condensation. It appears the roof consists of a plastic sheet with the roof tiles / slates behind this. The plastic is wet and has water dripping from it. Pics attached.

Image

Image

I was planning on insulating the gaps between joist with fibreglass but worried it will just get damp. Will the fibreglass keep heat in and prevent the condensation or does anyone any other advice ot tips?

Thanks
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Postby nige-s » Sun Nov 21, 2010 2:19 pm

scott,
you need to ventilate the roof space. nowadays we use breathable roofing felt which eliminates the problem you have. do not insulate between the rafters as this not achieve anything (if not more problems). looking at your pictures it looks like your loft insulation goes tight into the eaves which with your type of felt shouldnt be the case, pull back the insulation, vent the soffit if poss and put some slate vents in..(surprised this wasent done when the roof was re-slated?) and your problem should be cured..top insulation up to 200mm..

regards

nigel
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Postby scott b » Tue Nov 23, 2010 3:37 pm

Thanks. I had a roofer round today who priced me up some roof vents. (1 every 2 meteres.) Says I'm looking at about £2000 to sort it out. :shock:
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Postby oliver4649 » Fri Dec 31, 2010 6:51 pm

scott b wrote:We suffer with bad condensation on our windows and plasterwork around them. I have just been in the loft and found that the roof is covered in condensation. It appears the roof consists of a plastic sheet with the roof tiles / slates behind this. The plastic is wet and has water dripping from it. Pics attached.

Image

Image

I was planning on insulating the gaps between joist with fibreglass but worried it will just get damp. Will the fibreglass keep heat in and prevent the condensation or does anyone any other advice ot tips?

Thanks
IV GOT THIS TYPE OF MENBRANE PLASTIC in my gable end loft im a timber build home this menbrane does not seem to breath and gets condensation on i have vents in all place and still does not cure.
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Postby WARMSEALEXPERT » Sun Dec 22, 2013 10:03 pm

The roofing felt used by the re-roofer was totally unsuitable, to make it worse you have indequate ventilation at the loft soffit /eaves, and the top roof ridge, this is what is causing you're condensation problem,

The easist cure in this case is to clear out all the eaves, and make sure that this eaves to soffit slope/area of around 16" is clear open and free of fibreglass stuffing. Clear the eaves -then to go back again and partially close 2/3rds of them with a strip of 6" inch wide strip of ordinary DPC damp-proof course stapled across 'the eaves mouth" - *leaving a 2" space on the top-side (of it) to act as an *2" air vent. < This will conserve heat.

The other 1/3rd in number of the 'eave openings' leave completely open, Guessing I'd say you should have around 32 eaves/ soffits vents in total, so partialy close 20 with a DPC strip, and leave 12 in total fully open. 6 on each side of the loft space.

STAGE 2. You will need a step ladder in the loft, climb up to the ridge and cut away on either side of the RIDGE (cut-away and remove) 6 pieces of x 9" inch strips from the existing roofing felt you have, cut away 3 strips on each side of the roof-ridge distanced equally apart (counting left-to-right) and if possible position these * 6 ridge vents to correpsond with the CENTRE POINT of the 12 open eaves/soffit vents made below, and thats the job done. If I was doing it, I would add a breathable membrane strip (maybe 24 foot long x 1 foot wide) and runn it along the entire underside length of the whole ridge, and for vent safety would still cut-away and leave completely open 6 number x 9" inch open ridge vents mentioned. I would ensure the job looked attractive and professional looking. My company have cured quite a few condensation problems, around 7700 roofs in this fashion - with no complaints.
It's a tough sort of a job to do, and labour intensive for 3 hours, but well worth it,
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Postby Perry525 » Tue Dec 31, 2013 8:04 pm

The condensation is due to your way of life!

You are producing a lot of water vapour, by cooking,
washing, breathing, sweating, probably drying things
indoors.
You can solve the problem by opening a window and
letting the water vapour escape into the cold, dry air
outside. Cheap almost no cost solution.

If you do this, some of your heat will go with it.

You can buy and use a dehumidifier, this will present
a cold surface in the home, which will collect the water.
And keep your heat in and drafts at bay.

You can fit and use extractor fans in the kitchen and
bathroom. Note: The fans will blow the water vapour
outside, along with your warm air. In so doing they will
pull cold air into your home, probably creating a number
of drafts. You can get round this by buying fans with a
built in heat exchanger, this will save perhaps 80% of
your heat.

You should avoid making holes in your roof.

When the wind blows over a roof, the roof acts like
an aircraft wind, it lifts the air, and creates an area
of low pressure, this low pressure tries to pull the roof
off your home. If there are holes, the wind pulls your
expensive heat from your home into the loft/attic and
out into the sky. Not very clever. And expensive.

Condensation forming on a plastic sheet does no harm.

If you really want to stop it, then you must stop the
water vapour from entering your roof. This means
sealing every hole and crack in the ceilings and
making the loft trapdoor water vapour proof. This is
very hard to do, as water vapour molecules are much
smaller than air and they can pass through wood,
for example.

After sealing the ceilings, you must paint them with
either laytex or gloss paint, both of these are water vapour
proof.

Once you have sealed access to the roof, the water
vapour will then condense on the nearest cold surface
usually the windows, this can be messy but, a few
towels will usually soak up the water. Try not to let
it soak into the walls.
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Postby WARMSEALEXPERT » Tue Dec 31, 2013 11:30 pm

Penny your post contains a lot of useful advice, but glosses over the fact that 4 out of 5 people have washers, cookers, showers and moisture in their homes with no noticeable problems? I can recall a British farmers roof the likes of which I'd never seen before, he had on is house corrugated iron sheets, a money saving idea chosen by him because steel sheets were cheap and clay or concrete tiles expensive. This roof was dripping water beads like Niagara, his house was part of an old 150 year old barn and controlled ventilation was needed. We advised him to seal the main doors and mend or recover the part-steel sheeted walls which were ramshackle (scrap) and to keep the main entrance door to the barn, which was 16 foot wide firmly closed in the winter, In the roof we cut two 10 inch holes, and put a mini stove pipe chimney 2 foot high on them, and problem solved, We had created a spiral light house effect.

With householders the answer his UNDER TILE BREATHABLE ROOFING FELT, a one way EXIT POINT membrane for trapped moisture, If householders on warm SUMMER days left the front door open for some hours, and kept all the upper floor bedrooms doors open just 2 inches it would dry the house out in preparation for winter. Wall Bricks can contain water, damp and moisture, and this can be felt by touching walls whilst you are walking upstairs. Not sure what you mean when you said "cutting holes in the roof," in my first post I said cut small EXIT gap holes/ vents in the *roofing* *felt* they have (not the roof) - to create excess moisture EXIT points. Building codes advise a ridge point gap is left, modern practice is to build in ridge tile vents which in a retrofit costs a £1000? maybe.
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