A friends just asked me if i can run some hot and cold water to a loft conversion hes having done.Its a terraced house and only hot and cold at the moment is in the olf coal house extension which is now a kitchen,so its probably go to travel equivalent of 3 storeys-he will be having and electric shower,toilet and wash basin installed-running froma combi for hot water.mains pressure is pretty good-would i get away with 15mm for hot and cold seems as hot will only be needed for wash basin?