Approved Document B sets a height limit of 4.5 metres above the ground for using a roof window as a room's exit. Turn the loft of a house with two floors into a room and its floor lies past that, which makes a protected stair the necessary exit, and the window then only brings daylight. Single-storey homes with rooms upstairs, bungalows and chalet bungalows among them, stay within the limit, so their roof windows can be the exit too. Wherever that is the plan, the clear opening must reach 0.33 square metres with neither side under 450 millimetres.
There is a practical side too. A room in the roof needs enough headroom to be used, which often decides where a unit can go, because the opening must sit where the slope is high enough to stand under. Measurements start at the floor, go onto the plan, and we tell you honestly if a position is too low to be comfortable.
The rule bites on conversions. A room that is already a bedroom, wanting only more light, does not usually raise it. A brand new loft bedroom does, so mention it when you first write and the visit will cover the stair and escape route as well as the window.
On the slope, one plain unit usually keeps the roofers busy for one or two days. Our 10-year workmanship guarantee is in writing, and the quote comes after the survey. To arrange a visit, use the survey form and mention the bedroom.