Flat roof maintenance: what actually needs doing, and how often

Drainage first, because everything else follows it

Water that leaves the roof cannot do much harm. Water that sits works on the seams, adds load, and on an older membrane accelerates everything. So the single most useful maintenance task is keeping outlets, scuppers and internal drains clear.

If water is still standing a couple of days after rain, that is not a maintenance problem — it points at either the fall or a blocked outlet, and only one of those is fixed by cleaning.

Seams, terminations and penetrations

These are the three places flat roofs actually fail, so they are what a check should cover. Seams for lifting or separation. Terminations where the membrane meets a parapet or wall, because water getting behind an edge travels a long way before it shows. And every penetration — vents, drains, skylights, old antenna mounts and abandoned equipment curbs.

The field of the roof matters least, which is the opposite of what most people assume.

Twice a year, plus after events

Once after winter and once before it is a reasonable rhythm. The winter check earns its keep in Maryland, because freeze-thaw cycling is harder on seams and flashing than the temperature range suggests.

Add a look after any significant storm. And — this is the one people forget — after any other trade has been on the roof. A surprising share of the commercial leaks we are called to were created by an HVAC or telecoms contractor who did their job properly and left a penetration behind them.

What not to do

Do not put a coating on as a substitute for a repair. Coatings have their place, but applied over a wet or failing membrane they trap the problem and make diagnosis harder later.

Do not let people walk it casually. Foot traffic on a membrane, especially in cold weather when it is less forgiving, causes damage that will not be obvious for a year. If equipment needs regular access, walkway pads are a cheap answer.

And do not power-wash it. It is a sealed surface, not a driveway.