Why do flat roofs leak at seams and drains?
Flat roofs hold water longer, so any weakness is tested repeatedly. Seams open as the membrane expands and contracts, drains clog and let water back up, and flashing at walls and curbs peels as it ages. The membrane field is often sound while a detail fails.
Freeze-thaw is a factor in northern Illinois. Water that gets into a seam freezes, expands and pulls the seam apart a little more each winter. A small gap in October can be a leak by February.
That is why a roofer will often concentrate on edges, penetrations and drains first, before condemning the whole roof.
Is ponding water a problem?
Yes, if it stays for days. Standing water adds weight, accelerates wear and mosses seams, and it often signals low spots, clogged drains or deck sagging. A small puddle that dries within a day is normal on some roofs, but a persistent pond should be investigated by the roofer.
Clearing drains and scuppers is the cheapest first step, and it should be done regularly. If water still stands, the cause may be a structural dip, which needs a roofer or an engineer to assess.
How do rooftop units and penetrations complicate a flat roof?
Every unit, pipe, vent and curb on a flat roof is a hole to flash, and every walkway to a unit wears the membrane. Heating and cooling units add weight, condensate and traffic. A roof with many penetrations needs more flashing, regular inspection, and a plan for who walks where during service calls.
Service visits are a quiet source of damage. A technician carrying tools to a rooftop unit can puncture a membrane with a dropped screwdriver or scrape a seam with a boot. Walk pads along regular routes protect the membrane, and a note in the maintenance file reminding service companies to report any damage helps too.
When units are replaced, the curb flashing is often disturbed. The roofer should be called when a rooftop unit is changed so the connections are re-flashed, not left to the mechanical contractor.
What does the Illinois license difference mean for a commercial building?
Illinois licenses roofers through IDFPR in two classes: Limited, for residential buildings of eight units or fewer, and Unlimited, for all building types. A commercial roof therefore needs an Unlimited licensee. The license number must appear on every contract and bid, and you can check it in the state's look-up.
The license guide shows how to verify a number. Ask the roofer for it before signing any proposal, and for proof of insurance appropriate to your building.
Building owners should also ask the village building department whether a permit or registration is required for the work.
How do I plan work around tenants and operations?
Agree the work hours, access routes, noise limits and protection for occupied spaces in writing before the job starts. Ask how the roofer will keep the building watertight at the end of each day, since a half-removed membrane is exposed to weather overnight.
For a warehouse or manufacturing space, the crew will need a plan for stock and equipment under any open section. For offices, noise and dust matter. A phased approach that exposes only a section at a time is a common way to manage risk.
