Costs of renovating a dormer
Many dormers from the '70s, '80s and '90s are still standing, but no longer meet modern requirements for insulation, comfort and appearance. The question then is: **renovate or replace**? Renovating saves the construction and is usually 30–50% cheaper than a new dormer, but it only pays off if the underlying construction is still healthy. On this page, we explain what a renovation entails, when it is sensible and what items to expect in a quote.
We don't quote rates — we explain how the price is structured.
What falls under 'renovation'?
A dormer renovation usually includes:
- Renewing exterior cladding (synthetic, zinc, wood).
- Replacing roof covering (often EPDM instead of old bitumen).
- Replacing window frames and glass (HR++ or triple glazing instead of single glazing).
- Additional insulation from the inside or outside.
- Renewing interior finishing (plasterboard, plasterwork, painting).
What does not change: the main construction (trimmer construction, stud framing) remains in place. This saves on demolition, demolition waste removal, and placement costs.
When is renovating sensible?
Renovating pays off if:
- The construction is still healthy (no rotten studs or sagging trimmer construction).
- The shape and size still suit you — otherwise, you will rebuild the same problem.
- You want to remain permit-free (renovation often retains this status).
- You primarily want to solve an appearance or comfort problem, not a lack of space.
Not sensible if:
- The trimmer construction or stud framing is rotten.
- The surrounding roof area is also in poor condition (in that case, tackle it integrally).
- You want a wider or higher dormer.
- The house is older and asbestos might be present — demolition costs then become dominant.
Hidden damage and risk of additional work
The biggest risk of renovation is what appears under the old cladding:
- Wood rot in studs or trimmer construction.
- Sagging of the roof due to water damage.
- Poor old insulation (often wet or subsided mineral wool).
- Woodworm in older constructions.
Request a prior inspection where at least the cladding is locally opened up. This provides a much more reliable quote than just a visual inspection. Always count on an additional work budget of 10–20% for hidden damage.
Improving insulation during renovation
A common reason for renovation: the existing insulation no longer meets standards. Two approaches:
Exterior insulation
When replacing the cladding, you can place extra insulation between the old construction and the new finishing layer. Advantage: no loss of interior space; disadvantage: higher quote.
Interior insulation
Cheaper and less invasive. Disadvantage: the interior space becomes 5–10 cm smaller per wall and thermal bridges at studs remain.
For both, the vapour tightness must be correct, otherwise condensation and wood rot will occur. This is not DIY work — ask a specialist.
Renovation versus replacement — when does it tip?
If the additional cost due to hidden damage exceeds 30% of the original quote, the calculation often tips: a new build is then comparable or cheaper in the long term, and you get a new construction with a new warranty.
When in doubt, request both quotes (renovation and replacement). An honest contractor will tell you when renovating no longer makes sense.
Comparison table
| Aspect | Renovation | Replacement |
|---|---|---|
| Costs | 30–50% lower | Higher (complete new build) |
| Size & shape | Remains the same | Free choice |
| Construction | Existing remains | New construction |
| Warranty | On new parts | On complete dormer |
| Planning permission | Often permit-free | Depends on size and location |
| Hidden damage | Risk of additional work | Not applicable |
Frequently asked questions
Short, honest answers to recurring questions.
- What does a dormer renovation cost?
- We do not list rates. Renovating is usually 30–50% cheaper than a new build, provided there is no hidden damage.
- Is a renovation always cheaper?
- No. With a rotten trimmer construction or sagging, replacement can turn out comparable — with a new warranty.
- Do I need planning permission for a renovation?
- Maintenance on an existing dormer is often permit-free. With significant changes in appearance (different material, different colour), an aesthetic review (welstand) might still be required.
- Can I also insulate during a renovation?
- Yes. Exterior insulation when replacing cladding or interior insulation are both options.
- How do I know if the construction is still good?
- Request an inspection where the cladding is locally opened up. A visual inspection alone is insufficient.
- How long does a renovation take?
- With a good construction, 5–8 working days. With hidden damage, considerably longer.
- Do I get a warranty on a renovation?
- Yes, on the new parts (window frames, roof, cladding). The existing construction falls outside the warranty.
- What does asbestos removal cost?
- Strongly depends on type and quantity. If found, demolition by a certified company is legally required.
- Can I replace the glass without renewing the cladding?
- Yes, just replacing the window frames is also possible. This saves on cladding and roof work.
- Does a renovated dormer add value for a sale?
- Yes, provided there is an invoice and warranty from a recognized contractor. DIY work provides less certainty during a sale.
Summary
Renovating is 30–50% cheaper than replacing, but only pays off if the existing construction is still healthy. Request a thorough prior inspection — hidden wood rot or a poor trimmer construction can drive up the bill. With additional work above 30%, the choice tips towards a new build, because you then also get a new warranty and free choice of shape. Maintenance renovation (cladding, window frames, insulation) is often permit-free — changes in appearance can trigger an aesthetic review (welstand).