by SPUD1701 »
Fri Jan 07, 2011 4:55 pm
Hi
With condensation when it appears usually it can be rubbed off with a damp cloth rather than what a wet mark from a leak would give.
The British standards for roof ventilation is dependent on pitch of roof, but generally low level vents should give equivalent of 10,000mm squared free air per metre and 5,000mm squared at high level, they should be fitted back and front elevations of the roof.
Check how much free air each vent being proposed by the roofer actually provides.
With the insulation if you have already got 200mm, I would suggest cross layering with an additional 100mm, this is to limit heat loss from warm downstairs escaping between timbers in very cold attic and reducing the chance of condensation occuring, like putting hot kettle to outside cold window - condensation.
If condensation allowed to form it will appear as droplets on the cold surface and fall back into attic, making it look like you have a leak.
It may however, also be worth checking that you do not have a roof leak anyway.
The chimney - should be vented where fire place once was, the flue when in operation was vented from fireplace up chimney and out to air, this has been blocked and old stale air has no where to go, so vent where fireplaces were.