5 Sneaky Flat Roof Drain Issues For Commercial Roofs


Commercial Flat Roofs (and Flat Roofs in general) are notorious for ponding.  Most of the time it’s due to drainage issues. If you have a commercial flat roof drainage will cause your roof to NOT last 30-50 years. In fact with drainage issues and ponding most likely not even half of that.  Whether your flat roof is in Orange County, Los Angeles, or anywhere else on planet Earth these are 5 Sneaky Flat Roof Dain Issues For Commercial Roofs that you need to be aware of!


Flat Roof Drain on Commercial Roof

Flat Roof Drain Issue #1 Location


Drains should not be located near or next to other rooftop objects like A/C units, vent pipes, or skylights. If the drain is located too close to other roof equipment such as A/C units, this could cause debris to get trapped and stuck which could clog up the roof drain. A clogged-up roof drain over time can cause significant damage to your commercial flat roof.


#2 Drain Level


One little-known fact is that flat roofs are not exactly flat they do have a slight slope AND for good reason. Drain almost always have to be installed in the lower section of the roof. A good commercial roofer will remove the existing plywood and lower the drain to include a square catchment area around the drain. This will help with the collecting of debris and keep the drain flowing.


#3 Strainers/Domes


Drain strainers with small mesh holes cause debris to get trapped and thus clog the drain. As for Dome strainers, they’re too high in profile and can cause debris build-up.


#4 Trees


Often overlooked, but if your property is near trees that are less than a foot away from your roof, that is bad news for the drains. Tree branches and leaves clog up the drain more than anything. So if you’re building is near trees make sure regular maintenance is part of your plan.


#5 Piping


Piping that leads from the drain CANNOT be too narrow. If it is the volume of water that needs to flow during rainstorms will not be able to, and cause major issues to your drain and roof.




The bottom line is flat roofs have different types of issues than slanted or sloped roofs. They’re going to need a bit of extra care. But with a great drainage system in place, your commercial roofing system will last a very long time! Just remember to check your roof once in a while and address minor issues before they become major ones. Doing so will save you money!

Skip to content