I have a 1930's semi. The roof is tiled directly onto the timbers, no felt in those days I gather. There is wadding / horsehair & plaster type mix that is used throughout the roof on the underside of the joins between tiles.
I want to line the underside of the roof (or part of the roof) to prevent the heavy rain of dust and dirt that comes down from ruining anything I store up there.
Whatever I use will need to be fixed to the underside of the roof timbers.
A neighbour has used plastic sheeting for this purpose, however I'm nervous of restricting ventilation to the timbers by doing the same.
I've bought some breathable roofing membrane from Screwfix (Item # 95917), which is described as:
"Breathable, high-performance pitched rool underlay made from polyolefin materials, producing high vapour permability and water-resistance. User friendly.
* Eliminates Roof Space Ventilation
The idea is to staple gun this to the underside of the roof timbers, for about two thirds of the roof.
My question is ... what considerations should I make when fixing up the membrane, ie: is it better to have the waterproof side on the inside or outside face... I can see arguments for both ways and keep going round in circles.
The last thing I want to do is introduce any kind of mould problem to the roof timbers.
The idea of a membrane is to carry water to the guttering in the event that a tile or tiles which become damaged or missing, what you are planning to do is a waste of time it should be on top of the rafters and dressed in to the guttering using felt support trays to stop rot and flapping felt
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