I have been quoted for a re-roof (tile) and the builder tells me that he has to use a thin membrane under the tiles due to building regs. I thought that the correct material was the traditional thick black coloured felt?
Can anyone advise please.
Assuming you have a loft in the roofspace (not a habitable room) the underfelt can either be a breathable membrane without cross ventilation of the loft space (but ventilation is required above the membrane) or standard slaters felt with cross ventilation of the loft space.
For a total re-roof your local BI will expect to be involved - check with them if they have any special requirements.