Dormer construction and install
From mobile crane on the street to the final lead flashing. What happens on install day, what can go wrong, and what to ask before you sign.
Short answer
How is a dormer built?
Two methods dominate. A prefab dormer is built in a workshop and craned onto the roof in one piece. A traditional dormer is framed on site, piece by piece. Both end with the same critical steps: structural connection, lead flashing, insulation and waterproofing.
Install day
Step by step
| Step | Prefab | Traditional |
|---|---|---|
| 1. Crane setup | Mobile crane on street | Usually no crane needed |
| 2. Roof opening | Tiles removed, hole cut | Tiles removed, hole cut |
| 3. Place structure | Dormer lifted in one piece | Framed up over several days |
| 4. Watertight by | End of day 1 | After 3–5 days |
| 5. Insulation + vapour barrier | Pre-installed | Installed on site |
| 6. Cladding + lead | On the same day or next | Spread over the week |
| 7. Interior finish | 1–3 extra days | Part of the build |
Risks
Where construction goes wrong
Checklist
Before install day
Checklist
What to confirm in writing
- 01Date, start time and expected end time.
- 02Whether a mobile crane is needed and who arranges it.
- 03Whether a street parking permit is needed and who arranges it.
- 04Same-day watertight plan, with weather fallback.
- 05Who removes existing tiles and where they go.
- 06Insurance for damage to your roof and your neighbour's car.
- 07Who handles waste removal at the end of the day.
- 08Whether you need to be at home for handover.
Read next
Related guides
Quick answers
Frequently asked questions
FAQ
Veelgestelde vragen
4 vragen · klik om te openen
01How long does an install take?
A prefab dormer can be lifted and made watertight in a single day. A traditional on-site build takes one to two weeks. Interior finishing adds extra days on top.
02Do I need to move out during the install?
Usually not. The roof opening is closed by the end of day one for prefab work. For traditional builds, you stay in the house but expect noise and dust.
03Who is responsible if it rains during the install?
The company is. A professional fitter never opens a roof without a watertight plan for the same day, including a fallback for sudden rain.
04What is hoisted onto the roof and how?
Either prefab elements or a complete one-piece dormer. A mobile crane on the street is the standard method; a hand crane is sometimes used for tight spots.
Conclusie
A good install is invisible after the fact: no leaks, no draughts, no callbacks. That outcome depends on the company's preparation and discipline far more than on the brand of materials.