Cost factors for dormers

Size

A wide dormer with three or four window frames naturally costs more than a narrow one. Not only because of material volume, but also due to heavier structural work and greater crane capacity.

Exterior material

uPVC is usually the most economical, followed by polyester and timber. Zinc is significantly higher. Trespa and Keralit fall into the mid-range.

Window frames and glass

A uPVC window frame with HR++ glass is typically the cheapest. Timber or aluminium window frames are priced higher. Triple glazing adds considerable costs, especially with large glass surfaces.

Insulation

The thickness and type of insulation influence the price. PIR per cm is more expensive than mineral wool, but provides higher Rc-waarden (thermal resistance values) at a limited thickness.

Interior finishing

Shell finishing is cheaper than complete delivery. The difference is often smaller than expected, especially if you calculate plasterboard, plastering, window sills, electrical work, and painting separately.

Exterior cladding and roof

EPDM, bitumen, or zinc for the roof each have their own price range. For the fascia board, timber is often more economical than aluminium or zinc.

Crane work and accessibility

A larger crane or a mobile crane with a longer jib costs more. Narrow streets, overhanging trees, or a tall house often translate directly into extra hoisting costs and logistics.

Planning permission

A project requiring planning permission entails extra costs: municipal fees (leges), drawing work, and possibly a structural engineer. With a permit-free project, these items are largely eliminated.

Construction

With wide dormers or complex roofs, a structural engineer may be necessary, and in some cases a steel profile. Both are substantial costs that sometimes only become clear during the measurement.

Extras: roller shutters, screens, fly screens

Exterior sun protection, screens, roller shutters, fly screens, and insect mesh can collectively become a serious expense. For sun-facing sides, they are often worth double their money.

Service and warranty

A supplier with a longer warranty period and clear service agreements sometimes seems more expensive, but lowers the risk of future repair costs. Always evaluate quotes including these conditions.

Why prices vary so much

The difference between quotes is often not due to a single item, but rather the sum of small choices: different insulation, a different glass class, a different frame, a different crane setup, a different warranty. Anyone comparing quotes line by line will quickly see where the difference lies.

Reading a quote technically

A quote of € 14.500 and one of € 18.700 for "the same" dormer almost always differ in matters that only professional reading will reveal. Go through the following points for every quote:

• Dimensions in millimetres (width × height × depth), not "approx. 4 metres".
• Rc-waarde of side walls, front wall, roof, and floor — stated separately.
• Uw-value of the complete window (frame + glass), not just the Ug-value.
• Type of foil on the inside (vapour barrier) and outside (vapour-permeable), including the brand.
• Lead flashing class or mention of a lead replacement with the manufacturer.
• Roofing: EPDM (quality label, thickness in mm) or bitumen (number of layers).
• Dismantling and removal of existing roof tiles and demolition waste — included or not.
• Hoisting work indicating crane size and possibly a street permit.
• Warranty period per component (lead flashing, window frame, fittings, insulation may differ).

A quote that does not mention these points is not "shorter and more convenient" — it is incomplete.

Hidden costs and additional work

Additional work is not dishonesty on the part of the contractor, but it is a frequent surprise. The largest items:

• Suspected asbestos material under the roof tiles — mandatory removal by a certified company.
• Modifying the meter box for an extra electrical group upstairs.
• Reinforcing the roof structure if it turns out the existing rafters cannot support the trimmer joist.
• Modifying central heating pipes for a new radiator in the loft conversion.
• Painting around the new window frame (often not included with timber frames).
• Modifying the chimney if the dormer is placed too close to it.
• Street permit and possibly a guarded hoisting zone.

Ask explicitly with every quote which of these items are included and which are listed as a provisional sum or excl. An average project has 5–10% of the main amount in unavoidable additional work.

Long-term costs

The purchase price is one moment; the costs over twenty years are another story. For a dormer with (for example) a lifespan of 35 years, calculate the following:

• Maintenance: annual inspection and a thorough service once every 5 years.
• Painting for timber window frames: every 6–8 years.
• Replacing rubbers and sealant: every 10–15 years.
• Energy costs: a dormer with an Rc-waarde of 4,5 and triple glazing saves hundreds of euros per year compared to minimally executed variants.

A dormer that is € 2.000 more expensive but lasts 50 years instead of 25, is significantly more economical in the long run — and provides more comfort in the meantime. Therefore, always calculate a quote based on total costs over the lifespan, not just the bottom-line figure of today.

Frequently asked questions

Brief answers to frequently asked questions on this topic.

Why do quotes differ so much?

Due to differences in material, window frame, glass, insulation, warranty, and logistics. Always compare based on specifications.

Is a cheap dormer bad?

Not automatically, but be alert for omitted components, light insulation, and short warranties.

Can I save money on a shell construction?

Yes, provided you handle the interior finishing yourself or through a reliable finisher.

How much extra does a crane cost?

Varies by location. With limited accessibility, this can increase substantially.

Should I always request three quotes?

It is highly recommended. Three offers make the difference in choices and quality visible.

Is the planning permission included in the price?

Municipal fees and drawing work are often quoted separately; ask specifically how this is handled.

How much does extra structural work cost?

A steel profile or structural engineer can become a serious cost factor for large dormers.

Is higher insulation always more expensive?

Per cm yes, but the additional cost is often limited and the savings on heating costs compensate for this over time.

Does the warranty count in the price?

Not always visible, but a longer warranty is part of the value.

How do I know if a price is realistic?

By comparing specifications and, in case of suspicious deviations, asking what is missing.

Summary

The price of a dormer is made up of many items: size, material, window frames, glass, insulation, roofing, interior finishing, crane work, planning permission, structural work, and warranty. Comparing quotes based on specifications — rather than the final amount — prevents comparing apples to oranges and reveals where the true differences lie.

Conclusion

You choose a dormer for decades. The purchase price is merely one number; just as important are lifespan, maintenance, and warranty. Paying slightly more for solid workmanship often saves much more on future repair costs. Therefore, view a quote as a whole: material, craftsmanship, and service combined.