Flat roofs work differently than their sloped counterparts. Without gravity to shed water quickly, these roofs depend entirely on membrane integrity. When that membrane fails, leaks follow fast.
San Diego has thousands of flat roofs on commercial buildings, additions, garages, and ADUs. Understanding how to maintain them prevents expensive problems.
Why Flat Roofs Need Different Care
Standing water is the enemy. Sloped roofs shed rain in seconds. Flat roofs hold water until it evaporates or drains slowly through scuppers and drains. Every hour that water sits on your membrane increases the chance of finding its way through.
UV exposure attacks differently on flat surfaces. A sloped roof presents shingles at an angle to the sun. A flat roof takes the full force of San Diego's intense UV radiation perpendicular to the surface. Membranes degrade faster under this punishment.
Thermal cycling stresses flat roof membranes continuously. San Diego's temperature swings—from cool mornings to hot afternoons—cause membrane materials to expand and contract. Over time, this movement breaks down seams and creates stress cracks.
Different membrane types have different vulnerabilities. TPO and PVC single-ply membranes fail most often at seams. Built-up roofing develops cracks in the coating. Modified bitumen can blister. Knowing your roof type helps you understand what to watch for.
Regular inspection should happen twice yearly and after any significant storm. Walk the roof surface if it's safe to do so. Look for ponding areas, bubbles, tears, lifted edges, and degraded flashing. Clear debris from drains and scuppers.
A flat roof inspection takes thirty minutes and can save thousands in water damage. Make it a habit.
Re-coating extends membrane life significantly when done at the right time. Most flat roof coatings need renewal every five to ten years, depending on the coating type and sun exposure. Waiting until the membrane fails defeats the purpose.
Preparation determines coating success. The surface must be clean, dry, and free of deteriorated material. Pressure washing removes accumulated dirt and debris. Repairs to any damaged areas must cure before coating application.
Coating selection matters. Elastomeric coatings handle the thermal cycling of our climate well. Silicone coatings resist ponding water better than alternatives. Acrylic coatings provide excellent UV protection. Your contractor should recommend based on your specific roof conditions.
Application timing requires planning. Coatings need specific temperature ranges and dry conditions to cure properly. San Diego's dry season provides ideal conditions. Winter application risks rain interruption that can ruin an uncured coating.
Drain maintenance prevents most flat roof failures. A clogged drain holds water on the membrane, accelerating deterioration and increasing leak risk. Clean drains quarterly and after any wind event that deposits debris.
Flashing around penetrations fails before the membrane field in most cases. Pipes, HVAC curbs, skylights, and equipment mounts create stress points. Inspect these areas carefully and address any deterioration promptly.
When repairs exceed maintenance, replacement becomes necessary. A membrane that requires annual repairs or shows widespread deterioration needs replacement. Continuing to patch a failing system wastes money that could go toward new roofing.
