TopCat
Putin fanboy
"The first requirement of this regulation is for the roof to be weather-tight. In the case of pitched roofs the document states that any roof will meet the requirement if it has overlapping dry joints, is impervious or weather-resisting, and is backed by a material which will direct precipitation which enters the roof towards the outer face (as with roofing felt)."

More than 20 years? Old building regs, things have changed a lot in the last few decades wrt regulations. If you're buying then ask a surveyor what the law was at that time, or if less than 10 they should have a NHB cert, and you can go back to the buidling. 
) acceptable methods of roof construction.
but it doesn't mean his house can't be warm
I merely mentioned it in passing as the Other Roof Option in Most Cases