The short answer
Two styles dominate UK commercial buildings. Flat or low-slope roofs, covered with membranes or asphalt, are typical on shops, offices, schools and blocks of units. Shallow double-pitched roofs, clad in profiled metal sheets or composite panels on a steel portal frame, are typical on warehouses, factories and farm buildings. Which is more widespread depends on the type of building you count. Curved, sawtooth and mansard roofs exist but are less usual.
Flat and low-slope roofs
A flat roof on a commercial building is rarely perfectly flat. It has a gentle fall, usually created by tapered insulation or a sloping structure, so water drains to outlets or gutters behind a parapet. Shops, offices, schools, health centres and apartment blocks are often built this way because the roof gives a simple, economical cover over a wide floor plate, leaves room for plant, and allows extra floors or solar later. It also suits a deep building, where a pitched roof would have to be very tall.
The coverings include single-ply membranes, built-up felt, mastic asphalt and liquid-applied systems. They are described in our guide to flat roof systems for commercial buildings, and in the simpler explainers on single-ply roofing and built-up felt roofing. The risks are drainage and detailing: a blocked outlet or a weak upstand can cause leaks, and ponding speeds up wear.
Shallow pitched roofs on sheds
Industrial and storage buildings are commonly steel portal frames, with a shallow double-pitched roof, running from eaves up to a central ridge. The covering is profiled metal sheeting or insulated composite panels, fixed to purlins, which are the horizontal members spanning between the frames. Translucent rooflights let daylight in, and gutters run along the eaves or in a valley between bays. The frame is quick and cheap to erect, spans wide areas without internal columns, and supports a lightweight roof.
You can read more about the cladding in our explainers on industrial roof sheeting and on composite roof panels. Common faults on these roofs are open laps, loose fixings, corroded cut edges, cracked rooflights and blocked valley gutters.
Why the two styles took over
Economy and speed explain most of it. A flat roof on a concrete or steel deck is the simplest cover over a large floor, and a portal frame with sheeting can be up in a matter of weeks. Both styles also leave the interior open and let services run freely under the roof, which is what a warehouse, store or open-plan office needs. Planning and height limits push towards low roofs, and insurers and building control add their own requirements for fire and insulation, which both styles can meet with the right build-up.
Maintenance habits differ. A flat roof is walked more often, for plant and cleaning, and its coverings need protecting. A shed roof is seldom visited, so faults can go unseen until a leak shows inside. That gap is why a regular inspection is worth having on either type.
Other styles you will meet
Several other forms appear on commercial buildings. Barrel-vault or curved roofs cover sports halls, workshops and some retail units, usually in metal sheeting or a membrane. Sawtooth roofs, with a row of angled slopes and glazed faces, were built to bring north light into factories, and many older ones survive. Mansard roofs, with steep sides and a flat top, appear on offices and mixed-use buildings in town centres. Hipped and gabled pitched roofs, covered in tiles or slate, are found on pubs, village halls, churches and older commercial buildings. Standing seam metal roofs, covered on our page about what a standing seam roof is, are a growing choice for new work.
Each style has its own failure pattern. Barrel vaults leak at laps and end details, sawtooths at the glazing and valleys, and mansards at the junction between the steep face and the flat top. A roofer who knows the building type knows where to look first, and a survey that includes the underside of the roof, not just the surface, shows where water has been getting in and for how long. That kind of evidence makes the repair plan much more reliable.
Which style is best
None is best in every case. The right style is the one that suits the span, the use, the budget, the planning context and the plans for the building. A flat roof gives usable space and an easy line, but needs good drainage and upkeep. A shallow pitched shed roof is fast and economical, but depends on its fixings and laps. Our guide to the best roof for a commercial building goes through the decision.
If your roof is an unusual style, an old one or in doubt, a survey is the way to find out what is on it. We photograph the roof, explain what each part does and tell you what it needs, with a fixed written quote after. The wider picture for business properties is under commercial roofing in Basingstoke.
Every roof is different. A free survey with photos settles it for yours.
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