Installing a dormer: the complete process
A prefab dormer install takes one day; traditional 3-5 days. Below you walk through what happens, what to prep yourself, and where mistakes occur. Foreknowledge prevents the most common complaints.
- Prefab build time
- 1 day install + 1-3 days finishing
- Traditional build time
- 3-5 days + 2-4 days finishing
- Open roof hours
- 3-5 h prefab, 1-3 days traditional
- Workday start
- 07:00-07:30
- Crew size
- 3-5 people (2 roofers, 1-2 carpenters, 1 crane op)
Day 1: prep and opening the roof
Scaffolding or crane arrives around 07:00. Tiles are removed and stacked on the lift platform, battens trimmed, the roof opening sawn out carefully with circular or reciprocating saw.
Inside, the team tapes plastic across the loft floor and covers precious items. Dust will inevitably settle — expect 1-2 mm of fine sawdust within a 5 m radius of the opening.
Day 1 afternoon: hoisting and placement
For prefab the element arrives on a low-loader around 11:00. The telescopic crane (40-60 t) hoists the 1,500-3,000 kg element onto the roof and seats it within 30-60 minutes.
Lead junction (200-250 mm continuous slab), roof penetration and first sealing follow immediately. By 17:00 the roof is watertight again. In traditional builds the frame is assembled on site and the roof stays tarp-covered overnight.
Days 2-4: roofing and finishing
Tiles around the cheeks are relaid (broken tiles replaced — 5-15% breakage is normal). Lead and zinc details finished, gutter adjusted if needed, rainwater downpipe hung.
Inside: gypsum board against the inner frame (12.5 mm), vapour barrier check, frames sealed and window handles mounted. With prefab this is mostly pre-fitted and only needs hooking up.
Final day: handover and checkpoints
Final handover with checklist: leak test (rain simulation with garden hose), window swing direction, latches, visual seal check. Written handover signed by both parties.
Ask for a 24-hour use-in report: how to ventilate the first week (extra moisture from materials), when first paint coat is possible (4-6 weeks after install for sealant/glue to cure), and what the warranty covers.
FAQ
- How long is the roof 'open'?
- Prefab: 3-5 hours. Traditional: 1-3 days with tarp overnight. On rain risk ask whether the job can postpone; good companies anticipate this and reschedule.
- Must I be home during installation?
- Strongly recommended at start (07:00) and handover (end of day). In between not required, provided the installer has agreed access to toilet and power.
- Will there be much mess inside?
- Yes. Fine sawdust within 3-5 m of the opening. Good installers cover beforehand; even so 1-2 hours of your own cleanup is realistic.
- Can I stay in the house during install?
- Yes, except in the loft itself. Noise 6-8 hours on install day (drilling, sawing, hammering). For people working from home: plan a day elsewhere.
- What if it rains on install day?
- Brief showers are usually fine; sustained rain or storm isn't. Installer decides in the morning. On <24 h cancellation usually no fee.