Owens Corning distinguishes blue-green algae staining from moss and other growth. It warns against scrubbing or pressure washing because these can remove granules
Owens Corning technical bulletin: Algae Growth on Asphalt Shingles Technical Bulletin.
What this means for your roof
Owens Corning distinguishes blue-green algae staining from moss and other growth. It warns against scrubbing or pressure washing because these can remove granules. Cleaning may be temporary, and algae-resistant granules do not address every kind of growth.
A useful question for your contractor
Ask for a professional assessment before choosing a cleaning method.
Ask for the answer to be tied to the actual roof condition and the exact product being installed. Keep the agreed repair or installation detail with your estimate and project photos.
Bulletin edition: August 2023. This is the date of the manufacturer source, not a claim that this website guide existed on that date.
Read Owens Corning: Algae Growth on Asphalt Shingles Technical Bulletin
This homeowner summary explains the cited bulletin. The complete manufacturer document and current product instructions govern the installation details. A requirement for one manufacturer or product should not be transferred to another without checking.