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Hi,

This is a small flat roof that joins to the house and main pitched roof.
Some background info:
It has never had any insulation between rafters and doesn't have insulation on top.
Timber roof joists/rafters with timber furring. Then plywood and then torch on felt.


We discovered the water ingress when we took the plasterboard down (as part of a different job). There was no water marks on the room side of the plasterboard. In other words we would never have seen the leak/condensation if we hadn't been doing another job.

I initially thought that it must be a leak but now i am thinking it could be condensation? Is clearly a historical problem, not new as the plywood is dark brown, has happened over many many months/years.

One further thing is that this is a semi detached and the corresponding neighbors flat roof has been re-done and insulated on top of the roof (warm roof). The area that we have noticed the damp/leak is right at the point that the neighbors roof meets ours.

Could it be the warm roof interacting with our cold roof? Not enough ventilation? Or do we stick with our initial idea that it is an actual leak?

Please note that we have had a professional roofer look at the issue and they did not mention condensation, they thought it was probably a leak. But they aren't necessarily correct!

All thoughts greatly appreciated. Thanks
 

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Classic example of poor construction. poor insulation, no vapour control barrier & no ventilation
 
Joined
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Classic example of poor construction. poor insulation, no vapour control barrier & no ventilation

Can you elaborate on this further?

It doesn't need a vapor control barrier as it's a cold roof.

Bad ventilation, yes!
 
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