How Much Does a Garage Flat Roof Cost?

Cost guides price flat roofs by the square metre, not by the building they sit on, so a garage roof is costed in the same way as any other flat roof of equal area. What follows comes from national cost guides and is not a Crown price list. A garage is usually one plain rectangle, which makes the sums simpler than they are for a house roof with valleys and dormers.

Measure the garage, work out the roof area including any overhang, and multiply by the rate for the system you prefer. That gives a rough guide only. Our answer on flat roof cost per m² explains why small roofs often come out above the sum.

A single garage has the smaller roof, so the total is lower, but the cost per m² is often higher than on a double because set-up costs are spread over less area. A double garage has more roof to cover, and the rate per m² can ease a little, though the total rises. Either way, some costs arrive once per job: delivery of materials, safe access, protection for the doors and walls, and removal of the old covering.

Whole-roof guides give a wider view. A Checkatrade piece on replacing flat roofs carries a table dated December 2024 that shows £2,800 to £7,500 for a whole roof. That date is a while back, so use it only as a broad yardstick for a garage.

Garage roofs are often simple rectangles, with few penetrations, which keeps the detail work down. Some have a drop at the front, a lean-to against the house, or a parapet wall to the neighbour. Each of those adds detail time at the edge or the abutment.

Look at each quote for a line saying whether VAT is in the total, and for the system and thickness it names.

The covering is only one part of the price. Under it sits the deck, the boards that carry the roof, and the condition of that deck often decides the final total. Garage roofs can leak for years before anyone notices, because few people look at the ceiling of a garage. By the time a stain appears, the boards may be soft and stained.

When a roofer strips the old covering, boards that are damp, rotten or delaminated have to be replaced before anything new is laid. The extent can only be known once the old covering is off, or from cut-outs at the survey, so a careful roofer will photograph the deck and tell you what they find. That is why one written price follows the survey, and why the quote should say how any extra boards will be handled.

Falls matter too. A garage roof that holds water points to a deck that has dipped or timbers that have shifted. BS 6229:2025 keeps a minimum finished fall of 1:80, so correcting a poor fall can add work. See our answer on the minimum fall for a flat roof.

Other extras are edge trims, new outlets and any timber repairs at the fascia.

Not every garage has a flat felt or rubber roof. Many older garages carry corrugated sheets, and some of those are asbestos cement. HSE advises treating any building from before 2000, whether built or refurbished then, as likely to contain asbestos. Do not drill, cut, scrub or break sheets yourself.

HSE classes careful removal of asbestos cement sheeting, kept in one piece, as non-licensed work. That covers weathered sheets with no serious damage, and the disposal route still has to be agreed before anyone starts. Its A14 guidance adds that AC roofs are always fragile, and that a job turns notifiable once sheets crumble and throw up dust. Ask any roofer how the sheets will be handled and disposed of, and which rules apply.

The disposal route is part of the cost, so it belongs in the written price. Swapping a sheet roof for a flat one means taking the sheets off first and building a deck beneath, which is bigger work than re-covering an existing flat roof.

Our repair or replace guide helps you choose, and the flat roofing page describes each system.