What actually happens on installation day

Short answer

A prefab dormer install is one day. The crane arrives at 7–8am, the roof is opened, the prefab box is lifted on, sealed to the existing tiles and made weather-tight by late afternoon. Interior finishing follows in the next 2–4 days. You do not need to move out — but plan to be out of the house during the open-roof window.

Morning: arrival, set-up and crane

• The crew arrives 7–8am and sets up scaffolding or a roof edge protection system.
• The crane is positioned in the street or driveway; if street occupation is needed, a permit should already be in place.
• Furniture in the room below is moved to the centre and covered.
• The first tiles are removed and the old roof structure is opened up.

Afternoon: open roof, lift, seal

• The prefab box is lifted onto the prepared opening in one piece.
• The crew connects the box to the existing structure, dresses the lead apron and re-laid tiles around it.
• The interior is sealed against draughts and dust.
• Glazing is checked, frames adjusted, and the first watertightness check is done before the crane leaves.

End of day: weather-tight

By late afternoon the dormer should be in place, watertight and locked. The crew tidies, removes the major waste, and walks you around the outside. The room below is dusty but usable. You can sleep in the house that night.

The days after

Interior finish — plasterboard, electrical points, painting, mouldings — takes a further 2–4 working days, usually with a single fitter or finisher rather than a full crew. Final handover (oplevering) happens at the end of this phase, with a written punch list of any defects to address.

Homeowner checklist for the day

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