Dormers and roof windows
Add a dormer or a roof window, give the roof a flared eave, and see how much more floor area counts.
In the video0:39
How to do it
Go to the loft and select its roof: click it under Roof in the panel on the right.
Under “Dormers and roof windows”, choose Wall dormer, Dormer, Box dormer or Roof window. It appears on a free part of the roof.
Set the roof side, the dormer’s own roof (gable, shed or flat), its width and its height at the front. “Area gained” shows how much more floor counts.
Drag the dormer or roof window along the roof in the plan. A roof window comes in the usual sizes, or the size you type.
For a flared eave, turn on “Flared eaves” on the roof and set where it starts and how much flatter it is.
Good to know
- A wall dormer (ark) stands flush with the wall below; a dormer (kvist) is set back from the eaves; a box dormer (takopplett) is a wide one with a flat roof.
- The ceiling under a dormer is its own, so the counted floor area, the headroom lines, the walls under the roof and the headroom over the stairs all include it.
- In 3D the roof opens around the dormer, and the dormer gets walls, a window and the main roof’s covering. Sections, elevations and plans show dormers and roof windows too.
- A flared eave changes the knee wall and the floor area only where it starts inside the knee wall.
Questions and answers
How much floor area does a dormer add?
Select the dormer: “Area gained” shows it by your country’s rule – in Norway the BRA by NS 3940, counted from the 1.9 m line. A wider dormer or a higher front gives more.
Does a dormer need a building permit?
In most countries, yes: it changes the roof and the facade. Your building authority decides what your case needs. House Madness gives you the drawings for it: plans, sections and elevations with the dormer in them.
Can a roof window be an escape window?
It depends on the country. In Norway, DiBK’s guidance calls windows in a sloping roof usually unsuitable for escape, so the rule check never rates one better than “To check”, while a window in a dormer can count. In Germany and Denmark a roof window counts when it is large enough – in Germany only when its lower edge is at most 1 m from the eaves, which goes for a dormer window too.