Costs of a 6-metre dormer
Six metres is substantial. On most terraced houses, you use almost the entire available roof width, leaving only the statutory distance to the property line on either side. Structurally, logistically, and legally, this is a separate category: heavier steel construction, almost always a structural engineer, and on an increasing number of roof areas, the permit-free status no longer applies. On this page, we explain what this means for the price structure and what risks you avoid with the right quotation.
We don't quote rates — we explain how the price is structured.
When is 6 metres viable at all?
For 6 metres you need:
- Sufficient roof width: on most terraced houses, this is tight. Count on at least 0.5 m distance to both sides of the roof plane, or more if the municipality requires it.
- Sufficient roof pitch: too steep or too shallow makes the construction disproportionately heavy.
- No protected cityscape: in protected areas, 6 metres is rarely viable in terms of aesthetic review (welstand).
If one of these is missing, a roof extension or ridge raising is often a better solution than forcing a dormer that is too wide.
Heavier construction
At 6 metres, you span a roof plane that can rarely rest on wood alone. Count on:
- A heavy steel main beam profile (HEB 160 or heavier, depending on load).
- Possibly two composite beams for unfavourable roof pitches.
- Reinforced foundation details in the existing construction (extra screw channel, support solutions).
The structural engineer is not optional here; many municipalities already require the calculation upon notification, even if the permit-free route is still open.
Planning permission: almost always required
Theoretically, 6 metres on the rear roof plane can be permit-free — in practice, you almost always get stuck on one of these:
- Distance to the sides of the roof plane — not achievable on narrow roofs.
- Aesthetic review (welstand) or protected cityscape — stricter as the intervention gets larger.
- Local additional requirements — some municipalities impose extra criteria for wide interventions.
Count on an environmental planning permit (omgevingsvergunning) involving drawings, structural calculations, and an aesthetic review. This is a serious process cost.
Logistics and crane
A 6-metre prefab dormer is a large, heavy element. The crane is always larger than for 3 or 4 metres, and in a city centre, a mobile crane with a long jib may be necessary. Sometimes the street has to be closed off — this incurs permit costs.
Ask the supplier in advance for an accessibility assessment with photos or an inspection. This prevents the crane from not fitting on the day of placement.
Window frames, glazing, and sun protection
For 6 metres, four or five window frames are standard. The glass area is large — this brings solar heat gain prominently into the picture:
- Facing south and west: sun-control glazing or external sun protection (screens) is practically essential.
- Facing north and east: extra glazing provides light without heat issues.
Airtightness of four or five window frames requires care; leaks across such a large width quickly lead to draughts and condensation.
Comparison table
| Aspect | 4 metres | 6 metres |
|---|---|---|
| Window frames | Usually 3 | 4 or 5 |
| Steel | Often HEA/HEB light | HEB heavy or double |
| Structural engineer | Often | Almost always |
| Crane | Standard to large | Large or mobile with jib |
| Rear roof planning permission | Often permit-free | Often required (distance to sides) |
| Construction time | 6–8 working days | 8–12 working days |
Frequently asked questions
Short, honest answers to recurring questions.
- How much does a 6-metre dormer cost?
- We do not list prices. The price depends on the steel construction, structural engineer, window frame type, glazing, crane, accessibility, and planning permission.
- Is 6 metres permit-free?
- Sometimes theoretically on the rear roof plane, but often not in practice — the distance to the sides is critical for narrow roofs.
- Does 6 metres always fit on a terraced house?
- Not always. Many terraced houses have too little net roof width after deducting the mandatory side distance.
- Is a mobile crane always necessary?
- Not always, but at urban locations or for large elements it is needed more often than for narrower dormers.
- What is the construction time?
- Prefab: 1 day for placement + 5–7 days for interior finishing. Traditional: 8–12 working days.
- Is sun protection mandatory?
- Not legally, but with large glass areas facing south/west, it is practically indispensable for a livable indoor climate.
- How many window frames will fit?
- Four or five. Four is standard, five provides a finer rhythm and smaller openings.
- What if the structural engineer imposes extra requirements?
- That is common for this width; sometimes a heavier steel reinforcement or an extra support point follows.
- Wouldn't a roof extension make more sense?
- For a substantial space requirement, often yes. A 6-metre dormer is a major intervention — a roof extension provides more headroom at comparable costs.
- What if the street needs to be closed off?
- Then municipal costs apply for a temporary traffic measure. Ask about this explicitly.
Summary
Six metres is the upper limit for a practical dormer. At this width, the balance shifts: heavy steel construction, almost always a structural engineer, the permit-free status no longer applies, and the crane requires extra attention. The price-per-metre is favourable, but in absolute terms you pay for heavier components and higher process costs. Consider whether a roof extension or ridge raising would provide a better balance between space and costs for your situation.