Costs of a 4-metre dormer
Four metres is the width that captures an entire bedroom: three window frames, space for a desk under the window area, and a noticeable sense of extra headroom. Structurally, it is also a turning point: at 4 metres, a trimmer construction is almost always used and sometimes a steel profile. This has consequences for both execution time and costs. On this page, we explain which items start to count at this size and how to avoid a cheap quote resulting in additional work later.
We don't quote rates — we explain how the price is structured.
What should be in a 4-metre quote?
A good quote for 4 metres contains:
- Construction: trimmer with reinforcement, often a steel profile as the main beam.
- Exterior: roofing, side walls, fascia board, roof trim, and possibly zinc corners.
- Window frames: three window frames, typically one turn-tilt between two fixed parts, or two turn-tilt and one fixed.
- Insulation: Bbl-compliant (Bouwbesluit) (Rc roof ≥ 4.7), side walls separate.
- Interior finish: plasterboard, plastering, wide windowsill, painting.
- Placement: crane (often larger), demolition of the roof slope, debris removal.
Ask specifically about: steel profile (yes/no + weight), crane size, and whether planning permission costs include or exclude municipal fees (leges).
Construction: why 4 metres is a turning point
For dormers up to about 3 metres, you can often execute the trimmer construction in wood. From 4 metres — especially with a steep roof pitch or a roof with a large span — a steel profile is common. That steel profile should be calculated on the drawing by a structural engineer.
This is a hidden cost item that discount quotes sometimes underbid: it states "trimmer construction" without mentioning steel. If the structural engineer arrives on location and it turns out to be necessary, additional work follows. Ask in writing whether a structural engineer or steel is included in the price.
Window frames, glazing, and connection details
At 4 metres, you typically divide three window frames. How you do that partly determines the price:
- 3× turn-tilt — most flexible but most expensive (three hinged parts).
- 1× turn-tilt + 2× fixed — most popular choice, balance between ventilation and costs.
- 2× turn-tilt + 1× fixed — middle ground.
The connection details between three window frames require more sealant, finish, and adjustment work. At this width, airtightness is more critical; leaks here cause later complaints about draughts and condensation.
Planning permission at 4 metres
On the rear roof slope, 4 metres is generally permit-free provided you meet the following conditions: a minimum of 0.5 m above the roof eaves, a maximum height of 1.75 m, sufficient distance to the sides, and no protected cityscape. On the front roof slope, an environmental planning permit is almost always required, including an aesthetic review (welstand).
Some municipalities apply additional requirements. A supplier should know the local rules for your postcode.
Common additional cost items
When reviewing a quote for 4 metres, pay explicit attention to:
- Steel construction — sometimes separate, sometimes included.
- Structural engineer — separate fee or included in project costs.
- Larger crane — can be a separate item of hundreds of euros.
- Electrics — sockets, switches, LED strip: rarely standard.
- Floor finish — windowsill and flooring in the dormer zone.
- Exterior painting to colour code — at an additional cost.
Comparison table
| Aspect | 3 metres | 4 metres |
|---|---|---|
| Window frames | Usually 2 | Usually 3 |
| Construction | Wooden trimmer | Often a steel profile |
| Structural engineer | Sometimes | More often required |
| Crane | Standard | Sometimes a larger crane |
| Price-per-metre | Average | More favourable |
| Rear roof planning permission | Often free | Often free (within Bbl/Bouwbesluit) |
Frequently asked questions
Short, honest answers to recurring questions.
- How much does a 4-metre dormer cost?
- We do not list prices. The price depends on material, window frame type, glazing, construction (steel yes/no), accessibility, and planning permission requirements.
- Is a 4-metre dormer always permit-free?
- No. Almost never on the front roof slope. Usually it is on the rear roof slope, provided it complies with the Bouwbesluit and is not in a protected cityscape.
- Is steel mandatory for 4 metres?
- Not always, but often it is — depending on roof pitch, purlin spacing, and property design. Ask in writing if this is included in the price.
- Why is the price-per-metre lower than for 3 metres?
- Fixed costs (setup, crane, demolition, disposal) are divided over more material.
- How many window frames fit?
- Usually three. With two wider window frames, you get larger glass surfaces and fewer mullions.
- How long does installation take?
- Prefab: 1 day for placement + 3–4 days for interior finishing. Traditional: 6–8 working days in total.
- Is a structural engineer included in the price?
- Not automatically. Request this explicitly.
- Which roof is the most expensive?
- Zinc — durable but the highest investment. Class III EPDM is a good middle ground.
- Are electrics included?
- Rarely standard. Specify whether you want sockets and switches.
- Does the position on the roof matter?
- Yes. Closer to the ridge sometimes requires a steeper side wall and a taller crane.
Summary
At 4 metres, you get more space for less money per metre, but the construction becomes heavier. Count on a trimmer construction and possibly a steel profile; ask in writing if a structural engineer and steel are included in the price. Three window frames require more connection work — the quality of the sealant and airtightness determines whether you will suffer from draughts or condensation later. Compare three quotes on identical specs and pay extra attention to the items "construction", "crane", and "planning permission".