Flat roofing is the part of the trade where the installer matters most, because almost every flat roof failure is a detail somebody formed rather than a product that broke. Manufacturer approval is real here in a way it is not on a tiled roof, since most flat roof guarantees are conditional on who laid the system, and that gives you something checkable before you choose.
Approval is the checkable thing
Single ply, liquid and many rubber systems are sold through approved installer networks, and the manufacturer's guarantee depends on the installer holding that approval and following the detail drawings. Ask which system is being quoted and then ask the manufacturer, not the contractor, whether the firm is approved for it. That single call filters more risk than any amount of review reading, and it costs nothing.
What to ask about falls and outlets
Ask what the finished falls will be and where the water will go, because a flat roof that ponds will fail whatever is laid on it. Where the existing firrings have sagged, ask whether the new roof corrects them or follows them. Ask how many outlets there will be and whether they are being renewed, since an old outlet in a new roof is the joint most likely to leak. A contractor who answers these easily has laid a lot of flat roofs.
Reading a flat roof price
The rate per square metre covers the covering and its labour. Separately there should be the strip and disposal, the deck if it is being renewed, the insulation and vapour control layer on a warm roof, the trims and upstands by the metre, and the access. Online calculators give an area times a rate, which sets an expectation and misses everything on that list, so use one to decide whether you are in repair or replacement territory and then compare real quotes against a single written specification.
Questions people ask about flat roof installers
Should a flat roofer be on a competent person scheme?
Where the work is controlled under the Building Regulations, somebody has to sign it off, and a scheme registered contractor can do that itself rather than sending you to building control. It is one of the few things about a roofing firm you can verify on a public register.
How long should a flat roof installation take?
A small extension or garage roof is commonly one to three days once the deck is exposed and sound. Longer where the deck is being replaced or the insulation upgraded.
Is the cheapest flat roof quote usually a different system?
Very often. A three layer bitumen system, a single ply and a fibreglass laminate on the same roof are three prices, and a quote that does not name the system has not told you which one you are buying.