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Cost · Prefab dormer

What does a prefab dormer cost?

A prefab dormer is built in a factory and craned onto the roof in a single day. It is the fastest and usually the cheapest route — provided the quote covers the things the headline price tends to omit.
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Short answer

A 3-metre prefab dormer typically costs €8,000–€13,500 installed in one day, with HR++ glazing and Rc 4.5 insulation. Premium cladding, triple glazing and difficult crane access can add €1,500–€4,000.

Realistic price ranges

  • Basic PVC prefab, 3 m: €8,000–€10,000.
  • Premium PVC / Trespa, 3 m: €10,000–€12,000.
  • Timber-clad prefab, 3 m: €11,500–€13,500.
  • Add per extra metre: €1,500–€2,200.

What a proper prefab quote includes

  • Factory-built dormer with insulation, glazing and cladding.
  • Transport to site and crane hire.
  • Roof opening, integration with existing rafters, lead apron and flashings.
  • Interior reveals, plasterboard finishing and skirting.
  • Waste removal and site cleanup.

Common add-ons that are not included

  • Permit application and council fees (€400–€900).
  • Street closure or parking suspension for the crane (€150–€500).
  • Painting or wallpapering after installation.
  • Electrical sockets and ceiling lights inside the dormer.
  • Roller blinds or built-in window dressings.

FAQ

FAQ

Veelgestelde vragen

01What does a prefab dormer cost in 2026?
Indicatively €8,000–€13,500 for a 3-metre prefab dormer including factory build, transport, crane and one-day installation.
02Is prefab really cheaper than building on site?
Yes, typically 15–25% less. Factory assembly is faster and avoids weather delays; the saving comes mostly from labour, not materials.
03Are prefab dormers lower quality?
Not inherently. Factory tolerances are usually tighter than on-site work. Quality depends on the spec sheet — insulation Rc, glazing, cladding system, lead detailing — exactly as for a built-on-site dormer.
Conclusie
Prefab is the right default for a standard roof on a standard house. The only thing to watch is that the headline price covers crane, leadwork and finishing — once those are in writing, the comparison becomes honest.