Can anyone advise please, lady on my own having new conservatory built, had to have building regs as tiled roof. I am unsure about my floor. It is dwarf walls with cavity, brick outside. Block internal. Where the French doors are, the Installer says that building regs for this area say floor screed cannot extend past inner wall. So I have a concrete base up to the inner wall where opening for French doors are then a strip of black polythene then another strip of concrete. Is this correct please. Many thanks.