Commercial Roofing Maintenance: Asphalt Roofing Stain Removal

Commercial roofing should be inspected at least twice a year for mold, leaks and other problems before they worsen. Over time, you may start to see some staining and discoloration asphalt roofing. The staining and discoloration is typically from mildew and fungal spores, like Gloeocapsa magma, that come from nearby plants and trees. If left untreated, the staining and discoloration could lead to the roof deteriorating, rotting and leaking. Here is how you can remove the staining and discoloration.

Use Bleach to Get the Stains

Fortunately, asphalt roofing stain removal can be easily done with common chlorine bleach that you may have lying around in the home. Most roofing contractors recommend using a solution that is made from 1 part household bleach and 4 parts water. For higher efficiency and effectiveness, you should add a splash of TSP, or trisodium phosphate, into the solution. This cleaning solution is quite concentrated, so be sure to wear suitable clothing and protective eyewear.

Spray the solution onto the asphalt roofing, and let it sit for a few minutes before rinsing the solution off with a hose. You will want to inspect the asphalt roofing once the solution has dried to see if there is still any staining or signs of stickiness or sliminess. If there is, the process may need to be retreated.

Avoid Damaging the Asphalt Roofing and Surrounding Plants

The chlorine bleach solution can be quite damaging on the asphalt roofing. Due to this reason, it is crucial that you approach the entire cleaning process with care. To avoid damaging the asphalt roofing when removing the stain, you will want to avoid scrubbing the roofing shingles with a lot of friction or using power-washing techniques. Friction can easily loosen and remove the granule coating of the asphalt roofing. Many property owners have a misconception that a more concentrated solution that may be left on the roofing surface for a longer period of time will be more effective. However, you should avoid this at all costs as it may end up damaging the shingles.

In addition, the solution can be damaging to the plants in the surrounding area. You want to spray down nearby plants before and after cleaning with a bleach solution to prevent the chlorine bleach solution from damaging the plants. Consider covering the plants when cleaning.

Problems with Using a Bleach Solution and Alternative Removal Strategies

While a chlorine bleach solution may be effective in removing staining and discoloration, it is not considered as a permanent solution. There are some problems with using a bleach solution to remove the staining that you should be aware of. They include:

  • Weakening the structural integrity of the roofing shingles.
  • Creating elasticity problems. This will cause the shingles to stiffen, become brittle and even curl up with time. If the bleach solution is not removed in an effective manner and residues are left, you may have to end up replacing the entire roofing, which can be a costly procedure.

There are other alternative removal strategies. Many roofing contractors recommend lye-based cleaning solutions that can be purchased in stores. You can also prevent staining and discoloration by installing zinc strips that inhibit fungal growth, using anti-growth sprays or replacing the existing shingles with resistant shingles that have a special additive in them. Most of these resistant shingles have copper granules in them.


Staining and discoloration on commercial asphalt roofing structures can be easily removed using bleach and other alternative techniques. By having regular inspections from a company like Align Roofing LLC, you will be able to easily spot staining and discoloration and treat it before it worsens and becomes a bigger problem.