Condensation problem with Tyvek

1 Nov 2008
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United Kingdom
I have just had my 1920's detached house roof re-tiled with large format clay interlocking tiles - Marley Domino. with the installation I have had Tyvek felt installed my problem is that I have lots of condensation forming on the inside of the roof.
The technical guy from Tyvek came out and said to cap off my chimneys (these were removed to loft floor level when roof was re-tiled) and to cap off the cavity in the wall as it was open into the loft. I have done this but still have large quantities of condensation.

I dont have any ventilation at the moment as Tyvek man said I dont need any with there felt but I am considering introducing Lapvents and soffit vents as I wish to convert part of the loft into a room and cannot have condensation forming behind the insulation. The floor of the loft space is also insulated to around 200+mm Will installing lapvents and soffit vents sort out the condensation ? I also have my combi boiler in the loft which could be adding to the problem.
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Your boiler should be balanced flue and not effect the loft at all, is it?
If its not then it needs a dedicated air brick or similar. It still would not effect the loft as far as condensation is concerned.

This condensation is, water vapour that originates inside your home.
Its cause is breathing, sweating, washing etc; all things that produce water vapour.

It probably is getting into the loft via a badly fitting loft trapdoor or the light fittings in the upstairs rooms or through the plasterboard ceilings.(plasterboard is transparent to water vapour and as much as 2.5 litres of water vapour can pass through an 8 by 4 foot sheet in 24 hours.)

Water vapour being lighter than air rises and makes its way to the nearest cold surface, where it condenses and becomes visible. Usually this is the nearest window, window frame or cold wall. In your case perhaps the walls are warm and the windows double glazed.

The preferred solution is to check the loft door fits tightly, to reduce the movement of rising air/water vapour and the light fittings and any other holes in the ceilings. If these are all a tight fit, and more or less resistant to air and vapour movement, then you are left with the plasterboard. Your can try painting the ceilings with a waterproof solution to hold back most of the water vapour, or take the route of pulling the ceilings down, fixing almost water vapour proof plastic sheets below the joists and re plaster boarding.

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