The opening should have a typical area of at least 1/20th of the floor area of the room served, unless it is a bathroom which can be any openable size.
Fel rheol, dylai arwynebedd yr agorfa gyfateb i o leiaf 1/20 o arwynebedd llawr yr ystafell a wasanaethir, oni bai ei bod yn ystafell ymolchi.