Having a Dormer Installed: What Does It Cost and What Do You Need to Arrange?

What does it cost to have a dormer installed?

These are the going guide prices for a dormer in Belgium in 2026. The amounts come from public price overviews and include installation.

Indication of going guide prices in 2026, including installation and excluding VAT, based on public price overviews. For a home more than 10 years old, renovation work usually carries 6% VAT; otherwise it is 21%. You will hear your exact price after a visit or in your quote, following the free consultation.

A wider dormer costs more, but it gets cheaper per metre. A 2.5-metre dormer comes to around €2,600 per metre, a 6-metre dormer to roughly €1,600 to €1,800.

These factors also determine what your dormer costs:

• the width and the height;
• the material, uPVC or timber;
• the windows: fixed glass or opening parts, HR++ (high-performance double) or triple glazing;
• the structure: if purlins have to be cut through, a structural calculation is often needed;
• a permit, with fees that differ from one municipality to the next;
• the interior finishing, which is not included in most prices.

Do you need a permit for a dormer?

In Belgium that depends on your region, your municipality and where the dormer goes. At the back of your home a dormer is sometimes exempt from a permit; at the front you more often need a permit (an “omgevingsvergunning” in Flanders, a planning permit in Brussels and Wallonia). What is exempt is set by the rules of your region and the regulations of your municipality.

These are the points the municipality looks at:

• the shape and dimensions of the dormer, especially its height and width;
• the distance to the ridge, the eaves and the sides of the roof slope;
• whether it goes at the back or on the street side;
• whether your home is protected heritage or lies in a protected townscape or village;
• whether an allotment permit, a spatial implementation plan or a municipal regulation applies.

Even a dormer that is exempt from a permit must comply with the building regulations, such as structural stability and the EPB (energy performance) rules, and with neighbour law. Ask the planning department of your municipality, or in Flanders start at the Omgevingsloket (the Flemish permit portal).

You apply for the permit yourself. If you have other plans besides the dormer, such as removing a load-bearing wall, check whether your renovation needs a permit item by item.

What still needs doing inside after the dormer is installed?

Once it is installed, the dormer is finished on the outside but not yet on the inside. The cheeks (side walls), the dormer ceiling and the junction with the sloping wall still need finishing, as does the inside of the window frame.

According to public price overviews, finishing just the inside of the dormer quickly costs €400 to €600 per metre of width, around €1,500 for 3 metres, and extensive finishing can run up to €3,000.

We charge fixed per-m² prices from our price list for this. A sloping wall and the dormer ceiling count as ceiling there, just like any sloping wall in a loft.

Prices from our 2026/2027 price list, valid from 1 September 2026. Prices exclude VAT.

An example: a loft with a new dormer, with 35 m² of straight wall and 30 m² of sloping wall and ceiling. Everything gets renovation fleece with one coat of paint in RAL 9010 or 9016. The measurements are an assumption.

The walls cost 35 × €18.99 = €664.65, the sloping surfaces and ceiling 30 × €26.49 = €794.70. Add the call-out charge of €99.99 and the whole loft is finished for €1,559.34, about what finishing just the inside of a 3-metre dormer often costs elsewhere.

If you only have the inside of the dormer finished, the job quickly falls below 50 m². Our price list has a surcharge of €249.99 for that. Include the whole loft in one go and the surcharge no longer applies.

A uPVC window frame does not need painting, and we do not paint it. If the frame is timber, you can have us paint the inside, from €99.99.

Isn’t a company that only installs dormers cheaper?

For the dormer itself, it can be. But such a company often delivers it finished on the outside only. The inside, the junction with the sloping wall and the rest of the loft are then up to you, with a second party, a second quote and a schedule of its own.

You then pay the fixed costs twice, and you have to coordinate who comes when. If the first party overruns, the second has to move too.

We take on the dormer and the finishing together, in one schedule: first the structural work, then the plastering or wallpapering, and last the painting. We start on the day we agree together.

So do not compare only the price of the dormer. Compare the total for a loft that is ready to live in.

How does it work when you have a dormer installed?

1. Enquiry. Request a quote or call us on weekdays between 9:00 and 17:00. Send a photo of the roof, the width you want and whether the loft needs finishing too.
2. Free consultation. We discuss the dormer and the finishing. You then receive a plan and a quote.
3. Permit. If a permit is needed, you apply for it before the work is scheduled.
4. Measuring up. If you agree, we measure up and check the walls. The final price and the schedule are then fixed.
5. Installation. Suppliers quote a delivery time of usually 6 to 8 weeks for a prefabricated dormer. Once delivered, it is often on the roof in a single day.
6. Interior finishing. Our wallpaperers, plasterers and painters finish the loft.

The structural work is done by four in-house contractor teams of four people each. The finishing is done by our 97 in-house tradespeople: 40 wallpaperers, 32 plasterers and 25 painters. We are also currently renovating 150 shops.

You pay nothing upfront: 50% on the first working day, once all materials are on site and we have started, and 50% on completion. We work throughout Belgium.

If the dormer is part of a larger renovation, we can also take on the complete renovation of your home as your contractor, with a single point of contact.