How Long Does It Take to Replace a Flat Roof?

The answer starts with what the roof is. A 15 square metre garage and a 65 square metre rear extension are different jobs, even if both are flat. Cost guides use those same sizes as examples (Less, Oct 2026, for the garage; HomeBuilding, Sep 2025, for a three-bed semi roof), because area drives both money and time.

What else changes the number of days?

Four things matter most. First, the size and shape: a single clean rectangle goes down faster than a roof with a dormer, two rooflights and an awkward return. Second, the amount of detail: every upstand, trim and outlet is hand work. Third, what is found when the old covering comes off. Rotten boards or wet insulation are cut out and renewed before any new layer goes down. Fourth, the system itself, since a covering that needs curing time behaves differently from one that is bonded and walked on soon after.

Access plays a part as well. A roof reached by a side passage needs materials carried through, while a roof reached from a drive can have them lifted straight up. Scaffolding, where needed, has to be arranged ahead of the start.

Whatever the material, the sequence is much the same. The old covering and any failed boards come off, the deck is repaired, a vapour layer and insulation go down if the design calls for them, and the waterproof covering follows, then edge trims and the final details.

Is EPDM quicker than felt or GRP?

EPDM, a synthetic rubber sheet, can be laid as one large piece and glued down, so the covering itself goes down quickly on a plain roof. The edges and upstands then take the time. Torch-on felt goes down in layers, each bonded with a gas flame, so a two- or three-layer system takes longer than a single sheet. GRP, glass-reinforced plastic, is laid wet: resin and glass-fibre mat are built up in stages and need to cure before the topcoat and trims, which makes weather and temperature part of the plan.

These are reasons, not promises. A roofer who quotes a firm number of days before looking at the roof is guessing, and the figure we give you reflects what the survey found. For how each material compares, see EPDM rubber roof installation and torch-on felt roofs.

A flat roof cannot be laid in the rain. Damp boards trap moisture under the new covering, and adhesives, resin and flame-bonded felt all need dry conditions to work.

What happens if it rains in the middle of the job?

A well-run job is planned so that the roof is never left open overnight. Work is done in sections, and each section is made watertight before the crew leaves. If a heavy shower is forecast, the plan changes: work stops, sheeting goes over anything exposed, and the day's task is moved. That can add a day or two to a job, and in a wet week more.

Weather is part of any outdoor programme, and cold matters as well, because resin and adhesives need a minimum temperature to cure, and the product data sheet sets that limit. We would rather the roof was finished a few days later and sound than rushed into a damp spell.

You are kept informed about each day of the work, including a day lost to weather, so a delay never comes as a surprise.

A few jobs before the start date make the programme shorter and the site tidier.

What should I do before the roof team arrives?

Clear the access route and any items stored on or against the roof. Move cars off a drive where materials will be delivered, so lifting and unloading are not held up. Tell your neighbours if the work involves a scaffold or a lift on a shared boundary. If a scaffold would obstruct the pavement or road, a licence is needed under Highways Act 1980 s169, and the scaffolder is the one to ask who applies. Somerset Council asks for at least 10 working days' notice, which is worth knowing when setting a date.

Consents come first. A listed house, a conservation area or a raised roof line each mean a call to the council before anything is ordered. Our answer on flat roof planning permission sets out the questions to ask.

Then the survey, and one written price, comes before any date is promised. If you have a roof in mind, send photos and the approximate length and width, and we can give you a sense of the scale of work before visiting. The main flat roofing page lists the systems we lay.