The short answer
A commercial roof typically lasts from about 10 to 20 years for built-up felt, 20 to 35 years for most single-ply membranes, and 40 years or more for well-kept profiled metal, with lead and zinc lasting longer still. Exposure, drainage, workmanship and regular maintenance move every one of those figures, so looking at your actual roof tells you more than any table.
Lifespan depends on the system
There is no single answer for a commercial building, because a unit can be covered in half a dozen very different materials. A warehouse may have profiled metal sheets on the main span, a built-up felt flat roof over the office block and a run of lead in the parapet gutter. Each part has its own lifespan, and the roof as a whole is only as good as the shortest-lived part that nobody is looking after.
The figures published by suppliers, trade bodies and cost guides overlap but do not agree exactly. That is normal. A manufacturer states what a product can do when laid well on a sound deck. A surveyor sees what happens after a decade of ponding water, blocked outlets and foot traffic from plant engineers. We read every figure as a typical range and then bend it to suit the building we are standing on.
Our guide to commercial roof systems explains how each build-up is put together, which helps when you are reading a lifespan figure and wondering what sits under it.
Typical lifespans by commercial roof system
The table gives typical ranges from published sources: cost guides, the Building Centre, GreenSpec, the Confederation of Roofing Contractors and manufacturers' own data. Where sources disagree we have shown the spread rather than picked a winner.
| System | Typical life | What decides it |
|---|---|---|
| Built-up or torch-on felt | 10 to 20 years, longer for good multi-layer work | Quality of the top surface finish and the number of layers |
| EPDM rubber | 20 to 30 years or more | Seam and edge detailing, ponding water |
| Single-ply PVC | 20 to 30 years, some products longer | The specific product and its certificate |
| Single-ply TPO | Commonly 20 to 35 years | Product, welds, exposure |
| GRP fibreglass | 25 to 40 years | Deck movement and the topcoat |
| Profiled metal sheet | 15 to 25 years to first maintenance, 40 years or more overall | Coating condition, cut edges, fixings |
| Lead sheet | 50 to 100 years on flat roofs | Lead code, drip spacing, expansion allowance |
Typical figures from MyBuilder, Less, GreenSpec, the Building Centre, CORC and Cladco. Real lives vary with how exposed the site is, how well the work was done and the care it has had since, so none of these is a promise.
What shortens a commercial roof's life
The commonest killer of flat and shallow commercial roofs is standing water. BS 6229:2018 recommends a minimum finished fall of 1:80, and IKO advises designing to 1:40 so the finished roof still reaches it. A membrane laid that way sheds rain. One that has sagged between purlins, or has an outlet set too high, keeps a pond for days after the rain stops. Ponding speeds up the wear of felt and can stress the seams of a single-ply sheet.
Blocked outlets and gutters come next. A box gutter, the lined channel that runs behind a parapet or between two roof slopes, fills with leaves, moss and windblown packaging. When it overflows, water goes over the wrong edge and into the building. Edge details such as upstands, copings and flashings, meaning the lead or membrane strips that seal the covering against a wall, fail before the field of the roof does.
Foot traffic is the third cause. Engineers servicing air handling units and rooftop plant cross a membrane in all weathers. Without walkway pads, the same path gets worn through year after year. On metal sheet roofs, the weak point is the cut edge, where the coating has been sliced and the steel is exposed; cut-edge corrosion is dealt with on its own page.
How to extend the life you have
Most of what extends a roof's life is routine and cheap. Clear outlets, gutters and valleys of debris every autumn and again after a storm. Keep plant engineers to marked walkways. Have the edges, laps and penetrations looked at by someone who can see the detail, not just the surface.
Repairing early costs less than repairing late. A blister in a felt roof, a lifted seam in a membrane or a split in a lead flashing is a small, local job in the first season. Left through a winter, it feeds water into the insulation and deck, and a small repair turns into a section of re-roofing. A written record of each visit also helps if you ever need to show an insurer what care the roof has had.
A planned programme of inspection and minor repair is what keeps a commercial roof at the long end of its range. We cover what a sensible regime looks like on our page about how often to inspect a commercial roof.
Knowing when the end is near
An ageing roof usually gives several signals together. The surface is crazed, split or covered in patches. Leaks return in new places after each repair rather than in the same place. The insulation under the covering is wet, which you find with a moisture survey or by lifting a section. The same defect has been repaired three or four times.
That is the point at which the cost of the next repair needs weighing against a new covering. Whether to repair or replace a commercial roof is set out as a set of decision rules, and the cost drivers are on the commercial roof cost page.
If you are wondering about the age of your own roof, ask for the original specification, any guarantee paperwork and past repair invoices. If they are missing, a survey can still read the build-up from the layers. Our survey costs nothing, and afterwards you receive a fixed price on paper with pictures of what we found. Other services for businesses sit under commercial roofing in Bath.
