On an aging Ontario flat roof we walk a fixed route: drains and low points first, then the full perimeter and parapet, then every curb and penetration, then the field membrane and its laps, then the underside of the deck from inside. Each checkpoint tells you something different about how much life is left.
Why inspect in a set order rather than wandering the roof?
Because a roof fails in a predictable sequence, and walking it in that sequence stops you from missing the parts that matter. The details carrying the most movement fail first, the drainage failures accelerate everything else, and the field membrane is usually the last thing to go. An inspection that starts in the middle of the field and works outward tends to record cosmetic surface condition and miss the transitions that are actually letting water in.
There is a second reason. An aging roof is a capital decision waiting to be made, and the decision needs comparable data year over year. If the same checkpoints are recorded at each visit, in the same order, with photographs from the same positions, you get a trend rather than a snapshot. A trend is what tells you whether the roof has three more seasons or whether it is accelerating.
That is the difference between a look at the roof and a documented flat roof inspection. One produces an opinion, the other produces a record that ownership can act on.
Checkpoint one: drains, scuppers and low points
We start here because drainage failures cause more secondary damage than anything else on an aging roof.
- Are the drain baskets clear? Leaves, gravel, shrink film and packaging debris blown up from a loading area are the standard finds.
- Does the drain sit in a sump, below the surrounding insulation? On older roofs the sump often compresses, or a previous recover has raised the field without resetting the drain, so the drain sits proud and water rings it instead of entering it.
- Is the clamping ring tight and even, and is the target flashing intact? A loose ring is a direct path into the assembly.
- Are there overflow provisions? Overflow scuppers or secondary drains are what prevent a blocked primary from turning rainfall into a load problem.
- Where does water actually stand? Ponding shows as a dirt ring, a change in surface colour, or vegetation. Mark the low points and compare them against last year's photographs.
Standing water on an aging roof is not cosmetic. It adds load, holds organic debris against the membrane, freezes and expands inside laps through Ontario freeze-thaw cycling, and it hides the very defect that is leaking. The wider subject is covered in our post on flat roof drainage systems.
Checkpoint two: the perimeter and parapet
We walk the entire perimeter, every elevation, looking down at the base flashing and up at the metal above it.
- Base flashing height and adhesion. Is it run high enough up the wall, is it still bonded, and is there a gap behind the termination bar? Press it. Aging base flashing that has lost adhesion sounds and feels hollow.
- Cant strips. Present, crushed or missing at the wall junction. A sharp ninety degree turn without a cant concentrates stress on one line and splits.
- Corners. Inside and outside, at every change of direction. Corners split before straight runs because two directions of movement meet there.
- Cap and counterflashing. Open laps, backed-out fasteners, hardened sealant in reglets, rust perforation, and caps that slope back onto the roof rather than outward with a drip.
- Masonry above the flashing. Open mortar joints, spalled brick and failed caulking at coping joints put water behind the flashing regardless of how good the roofing is.
- Roof edge and gravel stop on roofs without parapets, checked for lifted metal and loose fastening.
On a Toronto or GTA building this is where the roof leaks first, because meltwater runs to the cold perimeter, refreezes at the parapet, and backs up behind the ice until it goes over the base flashing. The remedial side is on our roof flashing and siding page.
Checkpoint three: curbs, penetrations and rooftop equipment
Every object on a roof is a hole that somebody sealed. On an aging roof, each one gets checked individually.
- Rooftop unit curbs. Base flashing at all four sides and, critically, at the four corners. Look for flashing that has been cut to run new conduit or refrigerant lines and never reinstated. This is one of the most common findings on multi-tenant buildings.
- Curb height. Whether the curb still stands high enough above the finished roof surface, particularly if the roof has been recovered and the surface raised.
- Pitch pockets. Dished, shrunken or cracked filler around structural legs, guy wires and conduit bundles. Almost every pitch pocket on an aging roof is a maintenance item.
- Pipe boots and vent stacks. Cracking at the top clamp, hardened or split material.
- Skylights and hatches. Curb flashing, glazing seals, condensation staining, and cracked or brittle domes. Anything that will not carry weight is a fall hazard as well as a leak.
- Expansion joints. Covers intact, bellows not split, and joints not simply roofed over.
- Equipment supports and duct sleepers. Whether they are sitting directly on the membrane and abrading it.
- Condensate discharge. Where it lands. A unit discharging onto the membrane in one spot keeps that spot permanently wet.
Checkpoint four: the field membrane and its laps
Now the open roof. What is checked depends on the system.
SBS modified bitumen and built-up roofing
Look for loss of granules exposing the bitumen beneath, surface crazing and alligatoring, blisters, ridging over insulation joints, and open or fishmouthed laps. On a gravel-surfaced built-up roof, check whether the gravel is still embedded or has migrated, leaving bare bitumen exposed.
TPO and PVC
Probe the heat-welded seams with a blunt seam probe. Look for shrinkage pulling at fixed terminations, surface chalking, weathering and thinning at points of foot traffic, and punctures. Single-ply shrinkage shows up as tension at corners and at the base of curbs.
EPDM
Check seams and the condition of any tape-seamed laps, look for shrinkage, and check for pulled fasteners at plates.
All systems
Underfoot feel matters as much as what you can see. Soft, spongy areas indicate wet or degraded insulation. Fasteners telegraphing through the membrane indicate insulation that has compressed or a deck that is no longer holding attachment. Both of those are assembly findings, not surface findings, and they carry more weight in a replacement decision than any amount of surface weathering. Where the assembly is unknown, a test cut gives a physical sample of every layer at that point.
Checkpoint five: the underside, from inside the building
Half of an aging roof inspection happens indoors, and it is the half most often skipped.
Walk the top floor or the underside of the deck where it is visible. On a warehouse or plant with an exposed steel deck this is straightforward. Look for rust staining at the flutes, at side laps and at fastener points, water tracking marks, deflection, and efflorescence or spalling on a concrete deck. Check the underside directly below the low points identified on the roof.
Look at where interior stains have appeared and where they have not. Look at rooftop unit locations from below. Check whether interior humidity is high enough to be condensing at the deck, which is common in plants with process moisture and in buildings where humidification has been added without reviewing the vapour control in the roof assembly. Condensation damage looks like a leak, spreads like a leak, and is not fixed by roofing work.
Deck deterioration is the finding that changes everything. A corroded steel deck under a long-standing leak is a structural matter for a professional engineer, and it moves a roof from a maintenance conversation to a flat roof replacement conversation immediately.
What do the findings actually mean for the decision?
Findings sort into three groups, and the report should say which group each one is in.
- Maintenance items. Blocked drains, shrunken pitch pockets, open cap flashing laps, a split at one corner, debris. These are fixed on the next scheduled visit and they do not change the capital picture.
- Repair items. Localised wet insulation, a failed section of base flashing along one elevation, a drain that has to be reset, a split lap with moisture around it. These are scoped and priced as flat roof repairs and they buy real time on a roof with life left.
- End-of-life indicators. Moisture in several unrelated areas, splits appearing across the field, fasteners backing out, surfacing lost across the roof, repeated repairs in the same locations, and any deck deterioration. Once three or four of these are present together, further patching buys progressively less time.
The judgement is not about the age on the file. It is about how many of the third group are present and how fast they are multiplying between visits, which is exactly why a consistent annual record matters. For owners running several buildings, that record is what turns a roof from a surprise into a scheduled line, and our property manager services are built around producing it in a form that goes straight into a report.