Flat roofs dominate the NYC residential landscape. Brownstones, rowhouses, and most multi-family buildings have them. They work well when properly maintained and installed. They cause problems when they're not.
Here are the five issues we see most often, and what to do about each.
1. Seam Failures
Modified bitumen and EPDM roofs fail most often at seams, where two sheets of membrane overlap or where the membrane meets a vertical surface. These seams shrink and move with temperature cycles. Over years, the adhesive breaks down.
What to do: A seam failure caught early is a $200–$400 repair. Ignored for two seasons, it's a $2,000 section replacement. Inspect your flat roof's seams every fall before winter.
2. Drain Blockage and Ponding Water
Flat roofs need drainage. When drains clog with debris, water ponds. Ponding water accelerates membrane degradation and adds structural load. In winter, standing water that freezes expands and destroys membrane.
What to do: Clear roof drains twice a year: spring and fall. If you have chronic ponding in specific spots, the roof may need drain relocation or slope correction.
3. Parapet Flashing Failures
The vertical walls (parapets) at the edges of flat roofs need flashing to seal where the membrane terminates. This flashing takes constant sun, wind, and thermal movement. It fails more often than any other flat roof component.
What to do: Inspect parapet coping and flashing annually. Look for cracks in caulk, lifted edges, and areas where flashing has pulled away. Early caulk repair is cheap. Flashing that's fully failed needs to be replaced, not just recaulked.
4. Blistering
Blisters are bubbles in the membrane caused by trapped moisture or air. They look alarming but are often stable for years. The problem comes when they rupture.
What to do: Small blisters that aren't in high-traffic areas can be monitored. Large blisters or ones showing membrane damage should be cut open, dried, and patched. Don't walk on blisters. You'll rupture them.
5. Aging Membrane
Every flat roof membrane has a finite lifespan. Modified bitumen runs 15–20 years. EPDM runs 20–25 years when well-maintained. When the membrane approaches end of life, repairs become less reliable. Fix one area and another fails.
What to do: Know your roof's age and material. If it's approaching end of life, stop patching and plan for replacement. We can tell you exactly where your roof stands after an inspection.
