Cold Flat Roof Ventulation

[tbone83]

I'm insulating a cold flat roof above a bay leaving a 50 mm air gap.
The roof is old and isnt breathable felt there are no vents in the facia either whats the best way to add ventlation as there is no sofit?

Thanks

 

[noseall]

If ever there was a roof that would be better off as a 'warm deck' then yours is a prime candidate.

You could use mushroom vents but these look hideous.

There is also an abutment flashing vent system that allows roofs to vent via the flashing.

there are no vents in the facia either whats the best way to add ventlation as there is no sofit?

Thanks

You will have to find some way of standing the fascia off the roof joists allowing air to pass up and between the joists otherwise fit some louvered grills to the fascia.

 

[tony1851]

noseall; does it really matter about ventilation in this situation?
I might be wrong but I'm sure I read somewhere in the AD that small roof voids such as over a bay or porch don't need venting.

Where I am there are loads of flat-roof Victorian bay windows covered in lead (in the few cases where it's not been nicked of course!) and none seem to have any problem with rot; just wondering?