Commercial roof repair and leak diagnosis

The stain is not the leak

The single most useful thing to know about commercial roof repair is that the interior evidence is almost never below the entry point.

Water enters at a penetration, a seam or a termination, then travels — along the underside of the deck, along a purlin, down a structural member — and appears at whatever low point it reaches. It can surface twenty or forty feet from where it got in.

Repairing above the stain is therefore the most common wasted repair in this trade. It looks decisive, it costs money, and the leak returns with the next rain because the entry point was never touched.

How the diagnosis actually works

We trace backwards from the interior evidence and then inspect the likely entry points systematically. In practice, most leaks originate in one of five places:

Where the path is genuinely ambiguous after that inspection, water testing is the next step rather than a guess.

We photograph the cause, not only the repair. A close-out photo of fresh sealant tells you somebody was on the roof. A photo of the failed termination that was letting water in tells you what was wrong, and it is the record you need when the same building leaks again in three years.

Repair, or stop repairing

There is a point on every roof where continued repair stops being economical, and a contractor who never mentions it is selling repairs.

The signal is interval compression: each repair buys a shorter dry period than the one before it, and the repairs start appearing in different places rather than the same place. That pattern means the roof is failing generally rather than locally, and the next several repairs will cost more in aggregate than the replacement they are deferring.

When we see that pattern in a repair history, we will say so — and put the building into the survey and triage sequence described on the commercial roofing overview rather than booking another repair.