Flat roofs cover a lot of Midwest businesses, warehouses, churches, apartment buildings and plenty of homes with low-slope additions. They work hard, and when they leak, the drip inside rarely sits right under the problem. Here are the three causes we find most often, and why a flat roof leak shouldn't sit on the to-do list.
Cause one: water pooling that won't drain
A "flat" roof isn't supposed to be perfectly flat. It's built with a slight slope so water runs to drains, scuppers or gutters. When drains clog with leaves and debris, or the roof sags over time, water collects in low spots and sits there. That standing water, called ponding, keeps pressure on the roof surface day after day, works into seams, and finds every weak spot. If you see puddles on your roof a couple of days after the rain stops, that's a warning.
Cause two: seams that have pulled apart
Most flat roofs are made from sheets or layers joined together at seams. Summer heat, winter cold and the normal movement of a building put stress on those joints year after year. Eventually some of them open up. A gap you could barely slide a fingernail into is plenty for water to get under the membrane and spread.
Cause three: cracked flashing around edges and rooftop units
Anywhere something meets or passes through the roof, there's a joint that has to be sealed. Roof edges, parapet walls, drains, vents, pipes and rooftop HVAC units all rely on flashing. Foot traffic from service techs, weather and age crack it or pull it loose. These spots are some of the first places we check on any flat roof leak.
Don't wait. Small leaks spread
On a sloped roof, water runs down and drips fairly close to where it got in. On a flat roof, it can travel under the surface a long way before it finds a way inside. By the time you see a stain on a ceiling tile, the insulation under a much bigger section of roof may be soaked. Wet insulation stops insulating, adds weight, and keeps the deck damp. A quick repair now is a lot cheaper than replacing a big section later, and for a business, it keeps water off inventory, equipment and customers.
What to do right now
Move anything valuable away from the drip, put a bucket under it, and take photos. If it's safe and someone is trained to do it, check that roof drains aren't clogged. Then call a commercial roofer.
We do commercial roofs 24/7
John Beal Roofing handles commercial and flat roofs as well as homes, and we answer the phone around the clock. We'll find where the water is actually getting in, tell you straight whether it's a repair or a bigger job, and get it covered fast when it can't wait.
What John says in the video
Transcript: Why is my flat roof leaking? Usually, it's one of three things: water pooling that won't drain, seams that have pulled apart, or cracked flashing around the edges and rooftop units. Don't wait. Small leaks spread. We do commercial roofs 24/7. Call me, 1-800-JOHN-BEAL.
Frequently asked questions
What is ponding water on a flat roof?
It is water that sits on the roof instead of draining off. Standing water puts constant stress on the roof surface and the seams, and it finds any weak spot.
Why do flat roof seams pull apart?
Flat roofs are built from sheets or layers joined at seams. Heat, cold, movement of the building and age can open those joints, and once they open, water gets underneath.
Where do flat roofs leak most often?
At seams, at the edges, and around anything that goes through the roof, like rooftop HVAC units, vents, drains and walls, where flashing has to seal the joint.
Can a small flat roof leak wait?
It should not. On a flat roof, water can travel a long way under the surface before it shows up inside, so a small leak can mean wet insulation and damage across a much bigger area.
Does John Beal Roofing repair commercial flat roofs?
Yes. We do commercial roofs and answer 24/7. Call 1-800-JOHN-BEAL.
More answers from John Beal
- Can Clogged Gutters Damage Your Roof?
- What Happens During A Roof Inspection?
- How Much Does A New Roof Cost?
- All of John’s video answers
John Beal Roofing is family-run and has been roofing Midwest homes since 1947, serving Greater St. Louis, Kansas City, Columbia, Springfield, Lake of the Ozarks, and the Metro East and Carbondale in Illinois. Our Kansas City office is at 7440 NW River Park Drive, Parkville, MO 64152 (816-572-9500 Missouri side, 913-281-6000 Kansas side). Everywhere else, call 1-800-JOHN-BEAL. We answer 24/7.