The short answer
A single flat garage roof is usually a short job measured in days, not weeks, a pitched roof takes longer because there are more layers to strip and lay, and a cement-sheet roof adds testing, notification and careful disposal. Weather, access and what is found under the old covering move the schedule more than the size of the garage does.
What sets the pace
People expect the answer to depend on the size of the garage. In practice, size matters less than what has to be done to the roof. A single flat garage in felt or EPDM goes through a set of stages: strip the old covering, check and repair the deck, lay insulation or a vapour layer if specified, fit the new membrane and finish the edges. Each stage is quick on a small area, but they cannot be hurried or overlapped, because the deck must be dry before the membrane goes on.
A pitched roof adds scaffolding or edge protection, stripping tiles or sheets, replacing battens and underlay, then laying the covering and the ridge. A double garage is simply a larger version, though the extra width can bring a valley or a hip to deal with.
Access is the other big factor. A garage with a clear front and open drive is easy to work from. One in a narrow rear lane, with materials carried by hand, will take longer however skilled the team is.
Flat, pitched and sheet roofs compared
The table gives the shape of each job rather than a fixed schedule, because a real timetable depends on your own roof.
| Roof type | What the work involves | Main cause of delay |
|---|---|---|
| Flat felt or EPDM | Strip, repair deck, lay new covering and edges | Wet deck, rain, hidden rot |
| Flat GRP | Prepare deck, lay boards, laminate, cure, apply topcoat | Cold or damp weather stopping the cure |
| Pitched tile or slate | Scaffold, strip, battens, underlay, new covering, ridge | Rotten timber, lead and flashing work |
| Steel profile sheets | Remove sheets, check purlins, fix new sheets | Weak purlins, corroded fixings |
| Cement sheets | Test, notify if needed, careful removal, disposal, new roof | Waste carrier availability, breakage |
Our page on garage roof leaks explains how hidden damage affects a job, and why a roof that looked simple from below can turn out otherwise once it is open.
The extra steps for an asbestos cement roof
If the old roof is corrugated cement, three things come before the replacement can start. The first is identification. HSE's advice for pre-2000 buildings is to presume asbestos, and a sample test settles what you actually have. The second is method. Taking intact sheets down carefully is non-licensed work, yet sheets that are badly damaged, or likely to fragment as they come off, turn it into notifiable non-licensed work. HSE says the notice goes in before work begins, with no minimum lead time, so the delay here is usually paperwork.
The third is waste. For asbestos taken from a home, the contractor is the waste producer and fills in the consignment note, and the sheets travel to a site licensed to receive them. That step is logistics and forms, not hammering. Our guide to the broken asbestos sheet covers an emergency version of the same sequence.
Expect a cement-sheet job to take longer from first call to finish than a felt re-cover of the same size, even if the work on site is not much longer.
How weather and winter figure in
Rain stops a flat roof job, because the deck has to be dry. Cold affects adhesives, GRP resin and some sealants. A forecast that looks fine can still leave a damp deck at seven in the morning, so a careful team checks the surface before laying anything. Our separate page on replacing a garage roof in winter goes into which materials suit which conditions.
It is better to lose a day to weather than to seal moisture into a deck. A felt roof laid over a wet board can blister, and a GRP laminate applied in damp conditions can fail to bond. If a day is lost, the roof is left safe and watertight overnight, with the part that is open covered in a temporary sheet.
Concrete garage roofs are slower for a different reason: they are heavy and the work is bound up with propping, cutting and lifting. See our page on concrete garage roofs for what that involves.
Planning your own timetable
You can help the job run smoothly. Clear the garage of anything you do not want dusty, since roof work moves debris. Move cars and bins so the team can reach the structure and, if scaffolding is needed, so the scaffolders can get in. Tell us about gates, parking restrictions and any neighbours who share a boundary wall or a gutter.
On the day itself, expect noise from stripping the old covering, then quieter work as the new one goes on. Once the new roof is on, the drive is swept, the old covering leaves with us, and nothing is left for you to skip. The plan agreed after the survey is written down, so there is something to refer back to if the schedule moves because of weather or something hidden in the deck. Talk to us early about any date that really matters, for instance an inspection, a house sale or a family event, so the order of work can reflect it.
If you are on a tight timeline, such as a sale or a policy condition, say so at the start. We prioritise leaks and storm damage, and a garage letting water in is made safe before any planning of the full job. We still do not promise a start date before seeing the roof. Once the survey is done, you receive pictures of your garage and a written quote, which gives you a proper schedule to plan around. Our garage roof replacement page sets out the process.