The short answer
Replacing a garage roof is usually a short job compared with a house, because the area is small and access is simple. A single flat garage is the quickest, a pitched roof with new timbers takes longer, and an asbestos cement roof adds careful removal and disposal. We put a programme in writing once we have looked over the roof ourselves.
What decides the timescale
No two garage roofs take the same time, because three things drive the length of the job: the size of the roof, its shape and what is hiding underneath the covering. A single flat garage has one simple surface to strip and relay. A double garage with a pitched roof has two slopes, a ridge, verges and often a gutter run on each side, and each of those is a separate piece of work.
The covering matters as well. Stripping old bitumen felt is quick, but laying a new membrane has to follow the manufacturer's method, and some systems need a setting period before the next layer goes on. Fixing profiled metal sheets is fast once the purlins are sound. Slates or tiles are laid one course at a time, so a pitched garage in a natural covering takes longer than the same area in sheet.
The largest unknown is the condition of the structure below. A roof deck that looks fine from the ladder can turn out to be soft, and a rafter end that has sat in damp for years may need cutting out. We note what we can from the survey photographs, but the true picture only appears once the old covering is off, which is why a written timescale is a plan and not a promise.
Flat garage roofs
A flat roof on a single garage is normally the shortest job in this family of work. The old covering comes off, the deck is checked and repaired, insulation is added if the design calls for it, and the new membrane goes down with the edges, upstands and drip trim dressed properly. Cost guides report typical UK prices for flat garage roofs at about £700 to £1,000 for a single garage and £900 to £1,400 for a double (MyBuilder garage roof cost guide, 2026). A fixed quote follows once the survey is done.
What lengthens a flat roof job is nearly always the deck. A garage roof that has leaked for several winters tends to have damp boards, and replacing boards means cutting back, fitting new timber and checking the fall. A flat roof needs a slope so water leaves it: the BS 6229 figure quoted by one manufacturer is a minimum of 1:80, with 1:40 as the design target to allow for tolerances. Correcting a flat deck that ponds adds time but is worth doing before the membrane goes over it. For boards and falls in more depth, see the page on the garage roof deck.
Some single-ply and liquid systems are weather-sensitive while they are laid. A wet deck is not a sound base for a membrane, so a showery week can add days to an otherwise short job.
Pitched garage roofs
A pitched garage roof takes longer because there is more to it. Scaffold or edge protection goes up first. The old tiles, slates or sheets are stripped, fresh battens and underlay go on, then the new covering is fixed row by row. The ridge, verges and any leadwork then follow. Garage jobs lean on two parts: underlay, a secondary barrier under the covering, and battens, the cross-timbers to which each tile is hooked.
Ridge and verge work is slower than it looks. Since BS 5534:2014, ridge and hip tiles are not trusted to mortar alone, so each piece is fixed mechanically, or a dry-fix system takes the place of the mortar. Dry-fix means the ridge and verge are held by clips and screws instead of a bed of mortar, and BS 8612:2018 is the test specification for those systems. Either way, finishing the edges properly takes a good part of a day on a small roof.
If the roof is being converted from flat to pitched, allow longer again, because new timbers have to be designed and built. Our guide to a pitched garage roof explains what that involves.
Asbestos cement roofs
Many older garages in the area carry corrugated sheets made of asbestos cement. Their removal follows HSE guidance. Taking sheets off carefully, without breaking them up, is non-licensed work. Where the sheets are likely to be broken up in quantity and throw off dust and debris, the job moves into the notifiable category, and that adds paperwork before a start.
The sheets are lifted rather than smashed, kept intact where possible, sealed in wrapping and sent to a tip permitted to receive asbestos. All of that is slower than a standard strip-out, and the disposal step has its own logistics, which we set out on the page about asbestos sheet disposal. Unsure what the sheets are made of? Start with is my garage roof asbestos.
A job on a sheeted garage roof also tends to be sensitive to wind and rain. Large sheets catch the wind, and we avoid lifting them in poor weather, so the programme leaves slack for a lost day.
Weather, access and shared roofs
Weather is the part of the timescale nobody controls. Winter is not a barrier to garage roof work, and we cover the practicalities on the page about garage roof work in winter, but wind stops sheets and scaffold boards being handled safely, and heavy rain stops membranes being laid. A roof is never left open: each evening the working area is left weathertight.
Access shapes the day too. A garage down a narrow lane, behind a house or in a rear court needs materials carried by hand, which slows deliveries and waste removal. A block of garages also adds a layer before the work starts, because the roof may be owned jointly. If you are in that position, read who pays for a shared garage block roof before you ask for a start date.
Finally, think about what is inside. Cars, bikes, tools and stored boxes may need moving or covering. Clearing the garage the day before is a small step that saves real time on the day.
Permissions and what to expect
Most garage re-roofing needs no application, but some work does. The Planning Portal says repairs and re-covering normally sit outside building control while under 25 per cent of the building envelope and under 50 per cent of the roof are touched. A covering 15 per cent heavier or more needs approval too, with a structural check. Where approval is needed, the application runs ahead of the work and can set the start date. Our page on garage roof building regulations explains the threshold in more detail.
Once the survey is done, you get a written fixed price and the programme we expect for your particular roof. Clear the garage of anything that would be spoiled by dust or a stray shower before the old roof comes off, and move the car out for the days of the work. The quickest route to a firm timescale is to book the free survey through our garage roof replacement service.
