Is Moss On a Commercial Flat Roof Bad?

by | Feb 20, 2024 | Weather & Environmental Considerations

Yes, moss on a commercial flat roof is a bad thing. Moss will cause many different types of flat roof surfaces to wear faster than they would were the roof clean and will impede early identification and mending of roof problems.

What Causes Moss to Grow

The two main causes of flat roof moss growth are trees that overhang the roof and poor drainage in shady areas of the roof.

Why Moss Is a Problem

Moss surrounded by ponding on commercial flat roof |

Moss is a living thing. It grows and expands on the surface of the roof causing displacement, damage to the roof membrane, and obstruction:

    • On a shingle roof, moss can lift the shingles and allow moisture to migrate into the substrate.
    • On a flat roof, moss can open seams and cause moisture migration.
    • It can degrade the surface of the roof making it lose its waterproofing ability quicker than it otherwise would.
    • Moss can clump, break apart, and make its way into gutters and drains eventually causing rainwater to drain inadequately and pond on the roof surface.
    • Constant moisture can lead to unhealthy bacteria and mold growth.


Because the main causes of moss growth on a commercial flat roof is overhanging trees and poor drainage in shady areas, we recommend regularly pruning trees and maintaining your roof to ensure drain areas are kept clean.

The other thing we suggest is to power wash the roof surface every 5 years or so. Power washing removes the moss and enables an annual inspection of the roof so problems can be identified early, before they can develop into more significant and/or costly ones.

Commercial Flat Roof Inspectors on Roof |
If, during an inspection, some degradation is identified, a roof sealant can be applied to the area to help waterproof it. These simple actions can go a long way toward preventing moss from causing roof surface displacement, coating damage, and drainage obstructions. They will help ensure the health and longevity of your commercial flat roof system.

Expert Advice

Whether you’re a beginner, need advanced information about flat roofing topics, or a refresher,  this is where you can learn everything you need to know about commercial and industrial flat roofing.

Contact us for more information or pricing.




Jared Van Vranken is Vice President and lead estimator at Flat Roof Solutions in Malvern, PA. Jared has directed the installation, repair, recovery, and replacement of commercial flat roofs for more than a decade at Flat Roof Solutions. He guides clients in selecting the best roofing materials for their needs and budget.

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