Where flat roofs leak
Ponding water over a low spot, seams that have opened in the sun, the curbs under rooftop air conditioning units, drains that are blocked or set too high, and the parapet wall flashings where the membrane turns up. The open field of a membrane rarely fails; the details do.
A roof that ponds for days after rain is a roof that will leak eventually, whatever the membrane.
Repairs
Seams re-welded or patched with matching membrane, blisters cut and patched, curb flashings rebuilt with proper height and counterflashing, drains cleared and strainers replaced, and parapet caps resealed. Modified bitumen, TPO, PVC and older built-up roofs each need their own materials and methods, and mixing them fails.
I photograph before and after and keep a file per building so the next repair starts with history.
Recovers and replacements
When a membrane has aged out but the deck and insulation are dry, a new single-ply membrane can go over the old roof with a separation layer, saving the tear-off. Tapered insulation can be added at the same time to end ponding. Where the insulation is wet, a full tear-off is the only honest option, and a moisture survey tells us which.
A white reflective membrane on the recover cuts the building's summer cooling load noticeably.
Coatings
Silicone and acrylic coatings extend a sound roof's life and reflect heat. They are a maintenance step, not a cure for a failing roof, and they need a clean, dry, properly primed surface. Applied over a wet or dirty membrane they peel within a year.
For a metal warehouse roof with minor seam leaks, a seam-sealed coating system is often the best value.
For owners and managers
A yearly walk with drains cleared and seams checked, a written condition report, and a budget forecast for the eventual recover. Tenants are told to keep HVAC technicians off the membrane edges and to report ceiling stains the same week. That routine is cheaper than any emergency call.
I can take on several buildings at once and report on all of them in the same format.
Working around tenants
Membrane work is done in sections so the building stays dry and the business stays open. Noisy work is scheduled around the tenant's hours where possible, and rooftop units are shut down only as long as a curb rebuild takes. The manager gets a schedule up front and a photo report at the end.