Second hand box section rolled steel sheeting was laid on top of an existing but leaky felted roof. I am now finding that water is making its a way under the steel roofing and through the felt.
There are several possibilities... the sheets are secured with heavy duty roofing nails with a trapped plastic seal. The laps are screwed at 18" intervals but there is no mastic seal. The ridge cap is narrow so rainwater could splash and blow under.
I have in mind to fabricate a template/former in 12mm ply to fit tightly to the roof sheet, pierced with holes to allow conventional canned expanding foam to be fed into the ridge and form a tidy seal. Freehand attempts leave an unsightly bulge and reveals large gas pockets when trimmed.
How do I stop the foam sticking to the plywood? And, how long does it take before full expansion is reached?
Any other constructive thoughts?