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Felt has laps but membrane is just one continuuous sheet. (I have both - one each in 2 different roof sections)

Is it OK to fit these on the breathable membrane? I would have to cut slits for them to go in. I didn't know if I was OK to cut the membrane or if that would ruin it somehow. I already have a few lap vents in a felted section of the roof.

We have a small extension roof that joins into an older roof. The older one is felt, the new is supposedly breathable membrane. I'm feeling somehow the mix of both is causing problems with ventilation. Condensation is a major problem on plastic valleys where the two roofs join.

Is there by any chance a roof valley or some other smooth surface in contact with the membrane above that beam (hidden from view)? If so then I wonder if condensation is an issue, rather than an actual leak. What rings alarm bells for me is the fact it happens worse after rain - I have an...

I have that same type of valley on roof and get terrible problems with condensation on the underside of it, despite doing all I can for insulation and ventilation.

Call me paranoid but I don't believe the so called breathable membrane (used instead of traditional felt) in my extension loft is really all that breathable. I've had problems with mould and condensation (and yes I've ensured soffit vents are clear of lagging). Would it be OK if I cut a few...

Just seen this post. Do you still have the issue? I cannot offer a specific answer but all the chat has been around leaks or water ingress. I wondered if you'd considered condensation, formed internally, as the cause? If you cannot see any way that water's getting in, maybe it's not getting...

It already is insulated. Do you mean remove it and reinsulate from scratch. I don't have a vapour protection layer, just lagging direct on plasterboard. Is that the problem do you think?

Hi, I'm hoping somebody knows an easy fix for this. Our house has a small two-storey extension at the front so there are now two adjoining sloped roof sections on the house (see pic). All is fine but there's one problem. The two roof sections have plastic (not lead) roof valleys/channels...