The short answer
Protect people, stock and equipment first: move or cover what water could reach, isolate electrics where it drips near them, and catch the water. Then photograph the damage and call a roofer to stabilise the roof and trace the source. Where a leak comes from is often not where it shows, so the repair should follow a proper look, not a guess.
Protect people, stock and equipment
Water on a commercial floor is a slip hazard and an electrical risk. The first job is to keep staff clear of the wet patch and, where water is near sockets, lights or machinery, to switch off at the supply when that can be done safely. If in doubt, call an electrician.
Next, protect what can be moved. Lift stock off the floor, cover pallets and machinery with sheeting, and shift paperwork and equipment out of the drip zone. A bucket under a drip helps, but sheeting channelled into a drain can catch more. If water is gathering above a suspended ceiling, it may be safer to let it out deliberately through a small opening into a container than to risk the ceiling coming down.
Take dated photographs of the leak, the damage and the affected goods before anything is moved. They help any claim, and they help the roofer understand what happened. Keep receipts for any emergency costs.
Tell your insurer early if you may claim. Acceptance of a claim turns on your policy's terms, and nobody can promise an outcome, but early notice and good records are the basis of any claim. Our answer on commercial roof storm damage has the insurance detail.
Tracing the source
Water rarely drips where it enters. On a sheet roof it can run along the underside of a purlin or a lining for metres before it falls. On a flat roof it can travel through the insulation or along a deck joint from the real fault. A stain on the ceiling shows where water arrived, not where it came in.
Tracing it starts with the weather and the pattern. Does it leak only in wind-driven rain, only after a long wet spell, or at every shower? Wind-driven rain points to laps, flashings and wall junctions. Leaks after heavy downpours point to blocked outlets and gutters. A constant drip in dry weather can mean condensation rather than a leak.
On the roof, we look at the usual suspects: failed fixings and washers on sheet roofs, split laps and seams on membranes, lifted flashings at upstands, cracked rooflight sheets, and blocked or leaking gutters. We work from a safe position, never walking across fragile sheets, and we photograph each defect.
Where the source stays hidden, a hose test or a flood test, carried out in stages from low to high, can isolate it. Our guide to commercial roof surveys describes the process.
Making safe, and what a make-safe is
Our first step on a leaking roof is a make-safe. A make-safe is a temporary measure that stops water getting in while the proper repair is planned. It might be a tarpaulin secured over a damaged section, a patch to a split in a membrane, a sealed fixing, a replaced rooflight panel or a cleared outlet.
The aim is to protect the building and its contents until a lasting repair can be done, not to be the repair. Temporary measures can fail in the next storm, so they are checked and the next step is agreed straight away.
Access comes first. A commercial roof may be high, and wet in an emergency, so a safe platform, edge protection and sometimes a mobile access tower are needed before anyone works on it. Where the roof is cement sheeting, the asbestos position has to be known before it is touched, and nobody should stand on the sheets.
A make-safe also gives time to see the problem clearly. Once the water is stopped, the underlying cause can be found and priced without the pressure of an active leak. See our commercial roofing page for the repairs that follow.
From emergency to repair
After the make-safe, the question is whether the fault is local or a sign of wider failure. A single lifted flashing is a local repair. A membrane with many split seams, or sheets with widespread failed fixings, tells another story, and the choice moves to repair of the area, overlay or renewal.
We report what we found with photographs and lay the options out clearly, including the cheaper one if it is genuinely enough. The right repair is whichever fixes what is failing, and a patch on a roof at the end of its life only postpones the next leak.
You receive a single written total for the repair you choose, drawn from the survey, and nobody should quote before the roof has been inspected.
Keep the dated photographs and the report with your building records. If the same area leaks again, they show what was done, and they feed the maintenance plan described in our answer on commercial roof inspection frequency.
