What Should You Do to a Flat Roof After a Storm?

Contain the interior first, then document, then get the roof walked. Move stock away from active water, isolate any electrical service it is reaching, photograph everything with a time stamp, and record the weather. Then have a crew inspect the roof properly. Do not send your own staff onto a wet commercial roof to look.

What comes first, before anyone goes near the roof?

Interior damage usually outruns roof damage in cost, so containment is the priority in the first hour.

1. Move what can be moved. Stock, files, product and electronics away from the active water, and cover what cannot be moved.
2. Control where the water goes. A drum with a hose, or a bag taped to a small controlled ceiling penetration, is often better than buckets, because it directs the flow rather than collecting it.
3. Isolate electrical services. Have an electrician deal with any circuit, fixture or panel that water is reaching. Do not put people or standing water near live equipment.
4. Photograph and time stamp everything. Interior conditions, the water path, affected stock, and the weather outside.
5. Record when it leaks. Continuously, only in driving rain from one direction, or only during a thaw. Each points at a different cause.

Keep people off the roof during the storm and while conditions remain bad. Wet membrane, snow-covered skylights, standing water hiding soft spots and reduced visibility make a commercial roof genuinely dangerous, and the information gathered rarely justifies the risk. For active water entry, our emergency roof repair line handles the roof side.

What does wind damage look like on a low-slope roof?

Wind attacks the edges first. Uplift pressure is highest at the corners, then along the perimeter, then in the field, which is why fastener density is increased in those zones by design.

What a crew looks for after a wind event:

• Perimeter metal. Lifted, deformed or displaced edge metal, gravel stop and coping. Loose cap flashing that is now open at the laps.
• Peeled or billowing membrane. On a mechanically fastened single-ply, look for a change in how the sheet lies between fastener rows. Billowing that was not there before means fasteners have released or the sheet has torn at the plates.
• Ballast movement. Stone scoured from the perimeter and piled inboard means uplift has been working the surface. On a ballasted system that also means the hold-down has been reduced where the stone left.
• Base flashing pulled from parapets and curbs, and split corners.
• Impact damage. Debris carried by wind, branches, panels, unsecured rooftop items, signage, punctures membranes and dents metal. Anything on the roof that was not there before is evidence.

Wind damage often does not leak immediately. A section of edge metal that lifted and settled back is a leak waiting for the next driving rain, which is why the walk matters even when the ceiling is dry.

What does hail do to a commercial membrane?

Hail damage on a low-slope roof is frequently invisible from a distance and requires close inspection to identify.

On SBS modified bitumen, hail knocks granules loose and can fracture the bitumen beneath without breaking through. The visible sign is a scattering of impact marks with granules displaced, and granule accumulation in the drains afterwards. The fracture below the surface is what shortens the roof's life, and it may not leak for a long time.

On single-ply membranes, hail can puncture the sheet outright, particularly where it lies over a soft or unsupported area. A cover board makes a substantial difference here, because it supports the membrane against the impact.

On built-up roofs with aggregate, the stone absorbs a great deal of the impact, which is one of its functions. Damage is more likely where the aggregate has already been scoured away.

Hail inspection is systematic: a defined grid across the roof, close visual examination, and marking of impact locations. Rooftop mechanical units and their fins are checked at the same time, since they often show impact clearly when the membrane does not.

What does heavy rain reveal?

A heavy rain event is the most honest drainage test a roof ever gets, and the information is only available for a day or two afterwards.

Get the roof photographed within about forty-eight hours of the rain stopping. Anything still holding water at that point marks a drainage failure: a blocked drain, a compressed sump with the drain body sitting proud, a scupper above the low point of its area, or an area of insulation saturated in an earlier leak that has settled into a low spot.

Also check:

• Overflow provision. If the primary drains blocked during the event, did anything else carry the water? A blocked primary with no functioning overflow puts load on the deck rather than water off the roof.
• The debris line. Rain moves leaves, packaging and gravel toward the drains. Where that debris ended up shows you the actual flow paths on the roof, which sometimes differ from the design.
• New low spots. Compare against previous photographs. A ponding area that was not there last year usually means insulation has been saturated and has compressed.

This is why the file matters. Photographs of the same locations year after year turn one wet roof into a trend. The drainage design behind all of it is covered in flat roof drainage systems.

How is storm damage told apart from ordinary wear?

This distinction usually decides how a claim is handled, so it is worth understanding rather than arguing about after the fact.

Storm damage is sudden, has a mechanism, and is consistent with the event. Fresh tears with clean edges. Displaced metal with bright, unweathered fastener holes. Impact marks with sharp boundaries and no dirt in them. Damage concentrated on the exposed side of the building or in the uplift zones. Debris on the roof that matches the damage.

Ordinary deterioration is gradual and general. Crazing and surface loss across the field. Sealant that has gone hard and cracked at every lap uniformly. Shrunken pitch pockets. Corrosion and staining at a defect, which indicates the opening has been there through several rain cycles. Splits with weathered, dirty edges.

Two things make the distinction possible in practice. The first is a dated photographic record of the roof from before the event, which is one of the quieter benefits of a maintenance file. The second is prompt inspection, because storm evidence weathers. A bright fastener hole looks like an old one after a month of rain.

Where both are present, and they often are, the assessment separates the storm-related items from the pre-existing condition rather than treating the whole roof as one or the other. That report should be written honestly. Our approach to it is set out under flat roof inspection.

What documentation should you produce?

Assemble it while the event is fresh. An adjuster or an owner reviewing this six weeks later will only have what you kept.

1. Date, time and weather. The event, the conditions, and when the damage or water entry was first observed.
2. Interior photographs, time stamped, showing the water path, affected finishes, stock and equipment.
3. Roof photographs from the inspection: wide shots for orientation and close shots of each defect, with locations marked on a roof plan.
4. A written description of each failure, the likely mechanism, and whether it is storm-related or pre-existing.
5. The temporary work performed, what was done, where and when, with photographs.
6. Prior condition evidence. Maintenance reports, previous inspection photographs, past repair invoices.
7. A record of anything moved or discarded, before it goes.

Keep the temporary repair documented separately from the permanent scope. They are different pieces of work and they are usually treated differently.

What gets repaired now and what waits?

Storm response splits into two stages, and conflating them is how buildings end up with permanent repairs that fail.

Stabilise now. Stop water entering, protect the interior, secure anything loose that could become airborne or fall, clear drains so water has somewhere to go, and dry in open areas with a temporary membrane or a mechanically fastened patch. This is done in whatever conditions exist, because the alternative is more interior damage.

Repair permanently after. Once conditions allow, the assembly can be opened, the extent of wet insulation established by probing or moisture readings, the saturated material cut out back to dry, and the insulation, cover board and membrane rebuilt into the surrounding field. A permanent detail installed into wet insulation fails again, which is the single most common reason a storm repair does not hold.

The gap between the two stages is a scheduling and weather decision, not a preference. In winter it can be weeks. What matters is that the temporary work is genuinely watertight and that the permanent scope is written and booked rather than forgotten once the ceiling dries. The distinction is covered in detail in temporary and permanent repair solutions, and the wider storm response sequence in the Ontario emergency roofing handbook for property managers.

For storm damage on a commercial or industrial building in Toronto, the GTA or southwestern Ontario, our flat roof repair crews work from the interior evidence back to the roof. Call 416-456-0777.