Christian McArdle wrote:

hmm, I may have completely the wrong term for this - I can't see the
underside of tiles, there's a plastic membrane underneath them (& over all
the rafters) - the kind that is reinforced with an internal mesh.


Yes. It is this stuff (which would not be original) that prevents you fully
filling. That's unless you can read the make and it happens to be a
breathable membrane.


There's no requirement for BCO involvement in this is there?


Probably not. I just mean that there might be some difference in opinion on
whether soffit ventilation is sufficient for an apex roof. It may be
particularly troublesome if there is a rear "extension" with a valley join,
as is common on Victorian houses, as there will be no through ventilation on
those sections, particularly on the rear apex section between valley and
ridge.

BCO insisted on it on my roof, and impermeable membrane sarking.

Makes it bloody draughty up there I can tell you - way overkill IMHO.




Christian.