Loft ventillation

Postby tony77 » Sun Feb 22, 2009 8:49 pm


We have a roof with a fairly low pitch, and despite soffitt vents being instaled a while back, are suffering from considerable condensation during the cold snap.

I have had two roofers over to the visit the property, an 1885 brick built semi detached house.

One has recommended the installation of 6 tile vents costing around £425. The second reckons we need around 15 to adequately ventillate the roof at a cost of around £750-£800. There's early evidence of wet rot so we need to move quite quickly now to sort the problem out. There's quite a difference between 6 and 15- is the second one trying it on, or will the first quote prove insufficient? The house is three bedrooms- the neighbours on the other side also seem to get some condensation and already have some vents.

Any help much appreciated.

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Simply Build It

Postby eljaybee » Mon Feb 23, 2009 12:24 pm


What type of vents are they and at what centre?? are they both sides of the roof to give cross flow? the eaves aren't blocked by the insulation are they?
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Postby tony77 » Mon Feb 23, 2009 6:24 pm


I believe all three of the contractors I've spoken to are proposing to put tile vents in, positioned across the roof to provide the right kind of cross flow, obviously one guy thinks we need a lot more than others.

The eaves used to be blocked by insulation, but I believe most of this was pulled away to provide some air. We also have vents in the soffits- but these are apparently blocked up after being exposed to wind rain and dust over the years.

Do you believe tile vents will resolve the problem?
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Postby eljaybee » Tue Feb 24, 2009 9:35 am

Tile vents are one way to solve the problem but then again so would suitable and sufficient soffit vents. If you have existing soffit vents, and the air flow over the insulation, then why not replace those.

What type of soffit vent is it? a continuous strip or circilar vent every so-often? if the latter at what centres are they?? most builders think that these circular vents only need to be at 450 - 500mm centre when infact they should be at about 200 - 250mm centres to give the correct flow. Plus these are a lot easier and cheaper to fit!!!!
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Postby Perry525 » Sat Feb 28, 2009 6:20 pm

Condensation is caused by the way we all live, it gets there because we make it!

If you change the way you do things the condensation will go away!

Condensation in a loft is due to water vapour moving from the heated part of your home into the cold loft, probably through a badly fitting trap door, possibly through holes round light fittings or pipes.

As heat always moves towards cold and heat always rises, then the heat you put into your home carries the water vapour up into the loft where it condenses onto the nearest cold thing.

Water vapour comes from boiling kettles, saucepans, cooking in general, washing, bathing drying towels and other things on radiators.
We also breath it out and so do our dogs and cats etc;

The way to deal with it, is to block all the holes into the loft.
The make sure the bathroom and kitchen doors are always closed.
Use extractor fans in the kitchen and bathroom
and leave them running for twenty minutes after cooking or washing.

Open the windows for five minutes in the morning or at other times to let the water vapour out into the garden.

The outside air is nearly always drier than indoors, so as the wet air goes out dry air will come in.

If your concerned about loosing your expensive heat, buy and use a dehumidifier, this will dry the air and keep your heat indoors.
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