My bay roof leaked last week. The felt has lasted probably 30+ years, so it owes me nothing. Edge of (Victorian) decking a bit rotten, so the plan was:
Remove exg felt and deck, then, from the bottom:

18mm OSB3
75mm Pu (yes I know it should be 125, but aesthetics and space below a stone plinth dictate 75)
11mm OSB, screwed through the sandwich to the bay 'joists'
nailed felt underlay
Stuck felt underlay
Stuck top felt

BUT

Then I saw what was not holding the bay roof up, so I decided to replace the 11mm OSB with 6mm ply

AND THEN

It p-----d down with rain when I was half-way through getting the 18mm oSB on, so I had to rush like mad and get a temp cover of nailed underfelt on quickly.

So, to the Q:

Is there any reason why I should remove that temp layer when I fit the insulation, 6mm ply and felt? I don't think there is, but would appreciate some corroboration!

Cheers,

Nick

Thanks. Little bit ticky re the air leakage as the gap is (not!) 'sealed' by a rather moth-eaten Victorian moulding. I foresee lots of silicone!

Cheers.

Nick

Did wonder. May be too late now as I'm fighting time and weather! Whatever goes in/on will be better than before - nothing.

Thanks Timber. I questioned a diagram which showed the VCL where you suggest, as I thought it should be inside (where in fact no VCL ever was - it being a Victorian ceiling - but effctively now is due to maany years of vinyl paint), but I take your point. The temporary cover is polyester-reinforced bituminous underlay felt, which I think comes pretty close to impervious, and thus OK as a VCL.

Any more thoughts welcome, but if it does not rain I may have reached the point of no return by mid-afternoon!

Nick