Pressure washing lightly will remove the moss without damaging the shingles. Make sure to spray down the slope not up or you may cause a leak.
Moss on asphalt shingles indicates that organic material is collecting on the shingle giving the mold food to grow on. The overall slope of the roof may not be step enough for rapid draining and water is being retained on the roof.
- Trees should also be cut back away from the home to allow sun to dry out roof shingles.
- Shading, organic material collecting on roof, and a shallow slope to the roof can all lead to moss on roof.
Most importantly no chemicals are needed to solve your problem, just proper maintenance.