Short answer: The most common flat roof problems are ponding water, open seams, blisters, cracked flashing and clogged drains. Water standing more than about 48 hours after rain is a warning sign. Small problems can often be repaired, but widespread blistering, wet insulation or a soft deck usually means replacement.
Flat and low slope roofs are common on row houses, additions, porches, garages and modern homes. They work well when maintained, but they have their own weak spots. This guide explains common flat roof problems and repair options.
Common flat roof materials
- EPDM: a black rubber membrane, durable and flexible
- TPO: a white or light membrane that reflects heat, with heat welded seams
- Modified bitumen: asphalt based rolls, often torch applied or self adhered
- Built up roofing: layers of asphalt and felt topped with gravel, found on older buildings
Common problems
- Ponding water: water that stays more than about 48 hours after rain stresses the membrane and seams
- Seam failure: seams that open up, especially on older membranes
- Blisters and bubbles: trapped air or moisture under the surface
- Flashing leaks: at walls, parapets, chimneys, vents and skylights
- Clogged drains and scuppers: leaves and debris block water from leaving
- Punctures: from foot traffic, fallen branches or equipment
Signs of a flat roof leak inside
- Stains or drips on the ceiling below
- Musty smell in top floor rooms
- Bubbling or peeling paint near the top of walls
- Mold in corners of the ceiling
Repair or replace?
- Repair for a few leaking seams, a puncture, failed flashing or a small blistered area, if the insulation and deck are dry
- Replace when leaks are widespread, the membrane is brittle or cracked all over, insulation is wet, or the deck is soft
A roofer may take core samples or use an infrared scan to see how much insulation is wet before deciding.
Keeping a flat roof in good shape
- Clear drains, gutters and scuppers every season
- Have the roof inspected twice a year and after storms
- Keep foot traffic to a minimum
- Trim overhanging branches
- Fix small problems early
Read about roof repair and our guide on how to find a roof leak.
Quick answers: flat roof problems
Why is water pooling on my flat roof?
Low spots, clogged drains or a sagging deck. Water standing more than about 48 hours needs attention.
How long does a flat roof last?
It depends on the material and upkeep, often around 15 to 30 years.
Can a flat roof leak be repaired?
Often, yes, if the damage is limited and the insulation and deck are dry.
Which flat roof material is best?
EPDM, TPO and modified bitumen are all common. The best choice depends on climate, building and budget.
Who repairs flat roofs?
A roofer experienced with low slope roofs. Sifixit can connect you with a local roofer.
Related
This guide covered flat roof problems. For more background, see Ready.gov’s severe weather advice, and if you need help, Sifixit can connect you with a local provider.
This guide is general information for homeowners, not professional, insurance or safety advice for your situation.
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