Guides · Carpentry
Installing a Roof Window: Costs and Permits
No other intervention brings this much light into a house for this little money. What installation costs, when it needs a permit — and why the size chosen is almost always too small.
What installation costs
The guide price from our practice: CHF 3,000 to 8,000 per window, installed. At the lower end is replacing an existing window with the same size — old frame out, new one in, junctions redone. At the upper end is a new installation where there was none before.
Why a new installation costs more is carpentry: if the window meets a rafter, it is cut and the load is redirected via a trimmer to the neighbouring rafters. Add the insulation junction, vapour barrier, flashing kit and the interior reveal — sloped below, vertical above, so the light falls deep into the room. Four trades around a hole of one square metre. That is exactly why prices vary so much.
| Case | Guide price |
|---|---|
| Replacement, same size | CHF 3,000 to 5,000 |
| New installation with trimmed rafter | CHF 5,000 to 8,000 |
| Dormer | CHF 20,000 to 50,000 |
Add options that are worth it: an electric drive with rain sensor (important for high windows), external shading against summer heat — a roof window without external shading makes the room unusable in July — and triple glazing as a matter of course.
Does a roof window need a permit?
In the canton of Zurich the rule of thumb is: a replacement in the same size needs no permit. New roof windows of normal size go either without a procedure or through the simplified one, depending on the municipality — a call to the building office clarifies it in ten minutes. A dormer changes the roof shape and always needs the ordinary permit. In core zones and on protected buildings, the municipality has a say even for small windows. The procedures in detail: building permits in the canton of Zurich.
The most common mistake: too small
Almost every roof window we replace is replaced with a bigger one. The rule for living spaces: the glass area should be at least a tenth of the floor area, under sloped ceilings rather more. Two medium windows side by side add more living value than one large one — they distribute the light and frame the view. And height matters: the lower edge belongs low enough to see out while seated. If you want to convert the whole attic, the full calculation is in attic conversion. And if the roof is being renovated anyway, the window installation comes almost free — the scaffolding is up, the surface is open. More on that: roof renovation.
How a new installation runs
- Check position and rafters. Where the window sits, what carries load there, how big it can be.
- Clarify the permit question. One call, if in doubt a notification — before ordering, not after.
- Installation. Opening up, setting the trimmer, fitting the window, flashing outside, insulating and lining inside. One to two days per window.
Frequently asked questions
Can a roof window be installed in an occupied house?
Yes, easily. The work stays within one room, dust protection is part of the job, and by evening the roof is watertight again.
My old roof window fogs up and drips — replace or repair?
Fogging between the panes means the glazing is done. For windows over 20 years old, replacement is almost always worth it — new windows insulate twice as well, and the frame is usually as old as the glass. If it only drips in cold weather, it is often condensation, not a leak: a ventilation and insulation issue.
Roof window or dormer?
The roof window brings more light per franc; the dormer brings headroom and space. Rule of thumb: if light is the problem — roof window. If space is the problem — dormer, with a permit and five to ten times the cost.
More light under the roof?
Send me a photo of the room and one of the roof — I will tell you where a window belongs, whether it needs a permit and what it costs. As a carpentry business in Zurich we do the complete installation. The first conversation is free.
