The answer to 'lifespan of flat roof' is that a properly installed and maintained flat roof can typically last 10-20 years, depending on the roofing materials used. Flat roofs are more susceptible to damage from weather, foot traffic, and pooling water compared to sloped roofs, so their lifespan is generally shorter. With regular inspections, preventative maintenance, and timely repairs, a flat roof can reach the upper end of that lifespan range.
Flat roofing materials like modified bitumen, EPDM, and TPO have different expected lifespans, from around 10-15 years for built-up asphalt roofing to 20+ years for some single-ply membranes. Proper installation is critical, as is addressing any issues like leaks or ponding water promptly to avoid accelerated deterioration.