This is an inspection checklist for a commercial flat roof of any membrane type. It is ordered by how flat roofs actually fail: drainage first, then the details, then the field, then the inside of the building.
Walk it the same way every time and mark findings on a roof plan. A checklist worked through in a consistent order produces reports that can be compared year to year, which is where the value sits.
Before you go up
Check the access, the fall protection and the weather. A wet single ply membrane is slippery, a ballasted roof hides what you are standing on, and an older roof with wet insulation can be soft underfoot without looking it.
Take the roof plan, a camera, a probe and a broom. Note the date, the temperature and whether it has rained in the last day, because all three change what you will see.
Drainage
| Look at | What a problem looks like |
|---|---|
| Outlets and strainers | Blocked, missing, crushed, standing proud of the membrane |
| Sumps | Flat or filled, so water never reaches the outlet |
| Ponding | Standing water, or a tide mark and silt where it has dried |
| Falls | Water running along a lap or towards a wall rather than an outlet |
| Overflows and scuppers | Absent, blocked, or set too high to work |
| Gutters | Debris, vegetation, water held behind a joint |
Ponding is the finding that decides most of the others. Water that stands works on every seam it touches, loads the deck and keeps the insulation below it wet, so record how long it takes to clear as well as where it sits.
The details
| Look at | What a problem looks like |
|---|---|
| Upstands at walls | Too low, membrane pulling away, termination unsupported |
| Curbs under units | Flashing slipped, fasteners through the horizontal face |
| Pipe and cable penetrations | Sealant as the only detail, collars standing open |
| Corners | Patched rather than detailed, stretched or split membrane |
| Drain flashings | Clamping ring loose, membrane torn at the collar |
| Movement joints | Covered over, split along the line of movement |
The field
| Look at | What a problem looks like |
|---|---|
| Seams and laps | Open, fish mouthed, probing apart, sealant squeezed out |
| Splits and punctures | Anything through to the insulation or the deck |
| Blisters and ridges | Growing year to year, soft, or split at the crown |
| Surface condition | Crazing, chalking, loss of granules, exposed scrim |
| Underfoot feel | Soft, spongy or dishing areas, which suggest wet insulation |
| Fasteners | Backing out and tenting the membrane above them |
A soft area is the one finding you should not try to settle by eye. It means the insulation may be holding water, and the only way to know how much is a roof moisture survey or an infrared scan.
Rooftop traffic and equipment
Check whether the units are being serviced across bare membrane, whether condensate is discharging onto the roof rather than into a drain, and whether anybody has fixed a cable tray or a conduit through the waterproofing. Equipment added after the roof was built is responsible for a large share of avoidable leaks.
Inside the building
Finish indoors. Look at ceilings below the areas that concerned you, at plant rooms, and at the underside of the deck where it is visible. A stain inside is often the first evidence of a leak whose entry point on the roof still looks sound.
What to do with the completed checklist
- Split findings into urgent, planned and monitor.
- Mark every urgent item on the plan with a photograph.
- Get the urgent items priced as a single visit.
- Carry the planned items into the next budget cycle.
- File the plan and the photographs for comparison next time.
If the roof has never been surveyed, the commercial roof inspection checklist covers the wider building, and what happens during a roof inspection sets out how a professional works through the same ground.
Walked by Date Roof
Common questions
How often should a flat roof be inspected?
Twice a year as a working rule, plus once after any severe storm. The two scheduled visits bracket the seasons that do the damage, and the storm visit exists because wind and hail damage has to be found while the cause is still provable rather than months later.
- One visit before the wet season, one after it
- An extra visit after wind, hail or heavy snow
- Any roof with units on it needs more frequent checks
- A new roof is worth walking in its first year
- Clear the outlets between visits, not only at them
Frequency should follow the roof rather than the calendar alone. A roof with heavy rooftop traffic, a kitchen extract, nearby trees or a history of ponding earns more visits than a clean open membrane with nothing on it. Most warranties also require documented maintenance, so the inspection record is doing two jobs at once: finding problems, and keeping the warranty alive.
What is needed to inspect a flat roof properly?
A camera, a roof plan, a probe and a way of marking what you find. Nothing exotic. The equipment that changes the answer is the moisture survey gear, and that is a separate visit rather than something carried up on a routine walk.
- A roof plan to mark defects and photograph positions on
- A camera, with a wide shot before every close one
- A blunt probe for testing seams and soft areas underfoot
- Chalk or removable marker for anything needing a return visit
- A broom and a bag, because clearing an outlet is half the job
Record positions, not just defects. A photograph of a split with no context is almost useless three months later when somebody has to find it again, so take a wide shot showing a fixed reference such as a unit or a parapet corner, then the close detail. Mark the same position on the plan. That discipline is what lets one year's walk be compared with the next.
Can a flat roof be inspected while it is wet?
A walk can, and in some ways a wet roof tells you more. Standing water shows exactly where the falls have failed, and water finding a path shows where it goes. What cannot be done wet is an infrared survey, a seam test or any adhesion work.
- Ponding is easier to map while the water is still there
- Wet membranes are slippery, and some become dangerously so
- An infrared scan needs a dry surface and a temperature difference
- Seam probing and patch repairs need a dry substrate
- Photograph the water line before it dries and disappears
There is a real advantage in timing one visit for the day after heavy rain. Ponding that has drained away by the time the inspector arrives leaves only a faint tide mark, and a roof that drains in an hour looks identical on paper to one that holds water for two days. Everything else, including any testing and any repair, waits until the roof is dry.
Which flat roof defects need acting on the same week?
Anything letting water into the building, anything that will get worse with the next rainfall, and anything that is a safety risk. Everything else can wait for a priced program. The test is whether leaving it until next month changes what it costs to fix.
- An open split, lap or puncture with the deck exposed
- A blocked outlet with water already standing against it
- Lifted or loose edge metal, which the next wind will take
- A failed curb flashing above occupied space
- Any damaged rooflight or unguarded opening
Keep the urgent list short and specific, because a list of thirty items with no order gets read as a list of none. Give each urgent item a position on the plan, a photograph and a sentence on what happens if it is left, and the difference between a work order this week and a budget line next year becomes obvious to whoever signs it off.
Does a flat roof inspection include the drains and the parapet?
It should, and they are usually where the findings are. The field of the membrane is the largest area and the least likely to be the problem, while outlets, upstands, copings and edge trims account for most of the water that gets into a building through a flat roof.
- Outlets, sumps, strainers and overflow provision
- Upstand heights at every wall and curb
- Coping joints and the fixings holding them down
- Edge trim laps and the drip into the gutter
- Chases and reglets where the flashing is tucked in
Ask specifically whether the inspection covered the perimeter and the outlets rather than assuming it did, because a walk that stays in the middle of a roof is quick and tells you little. Where a parapet gutter is behind a wall and out of sight, it needs reaching or recording as inaccessible. An outlet nobody could see is a finding in itself.