It depends — just because it’s 20 years old doesn’t mean you should replace the roof, but you should be thinking about it.
If the integrity of the seams is still good, and membrane shrinkage is minimal, you can probably get several more years out of your roof with proper maintenance. When seaming starts failing, however, or if there is significant physical damage from rooftop activities, it can cost a lot to fix.
Another consideration is what’s in your building. If you have valuable equipment or if you have recently invested in some major interior renovations, you might want to minimize your risk and replace the roof. On the other hand, some EPDM roofs are warrantied for up to 30 years and do last that long.
Flat roof systems typically last from 10 to 30 years depending on: