A dormer window is the quickest and most effective way to transform a dark, cramped attic storage space into a full-sized additional bedroom, bathroom, or bright home office. But what does fitting a dormer window cost in 2026?
Heidstra Bouw constructs dormers and rooftop extensions across Friesland, Groningen, and Drenthe. In this overview, we lay out current prices, planning rules, and material options.
Benchmark prices for dormers in 2026
Total costs depend on width, exterior cladding materials (plastic/Keralit, timber, or zinc), and the choice between prefab installation or traditional bespoke timber carpentry built on site:
| Dormer Width | Indicative Cost Plastic (Keralit) | Indicative Cost Traditional Timber |
|---|---|---|
| 2.5 meters (1 bedroom) | €6,500 - €9,000 | €7,200 - €9,800 |
| 3.5 meters (Standard) | €8,200 - €11,500 | €9,000 - €12,500 |
| 4.5 meters (Wide room) | €10,000 - €14,000 | €11,000 - €15,500 |
| 6.0 meters (Double room) | €13,500 - €18,500 | €15,000 - €20,000 |
Prices include VAT, crane hire, debris disposal, structural timber alterations, and HR+++ triple glazing. Interior fit-out (such as plasterboard lining, skimming, and electrical sockets) is optional.
Prefab versus Traditionally Constructed
- Prefab dormer: Fully pre-assembled in our workshop and craned onto the roof in a single day. Ideal for standard roof pitches and swift installation with zero weather exposure risk.
- Traditional dormer (bespoke carpentry): Built directly onto the roof framework by our carpenters. Essential for non-standard roof angles, historic properties, thatched roofs, or bespoke dimensional requirements.
Building without planning permission under the Omgevingswet
Whether a dormer window can be constructed without planning permission depends on its position on the roof, dimensions, setbacks from the eaves and ridges, the municipal environment plan, and the heritage status of the building. A rear roof pitch and a front roof pitch often follow completely different rules. Always run the address-specific check in the Omgevingsloket; if a permit is required, we can prepare the architectural drawings and submit the application for you.
Have a dormer installed
Looking to create spacious living areas in your attic? Contact Heidstra Bouw via our building and remodeling service page or request a free quote.
