A fiberglass roof can look good as long as it’s clean. Luckily, cleaning it is simple. It doesn’t take long, although you’ll need to be comfortable working on the fiberglass roof.
Step 1 - Preparation
To protect the vegetation around the building, hose it down with water. After this, mix 1 gallon of warm water with ¼ cup trisodium phosphate and 1 quart of bleach. Decant this into a garden sprayer. With a broom, sweep any debris and dirt from the roof.
Step 2 - Application
Spray the solution all over the fiberglass roof, being certain that your spray gets into corners and crannies where dirt can collect. Allow it to sit for about 15 minutes so the solution can penetrate the dirt on the fiberglass roof.
Step 3 - Finishing
After the solution has had a chance to do its work you need to remove it. To do this, spray cold water from the garden hose onto the roof to take off all the solutions. If there are still dirt areas, repeat the procedure with the solution and then rinsing. Make sure you take off all the solutions when you rinse to avoid any future problems.