1. General: Simple roof cleaning guidelines for low-slope single-ply roof membranes are provided by the Chemical Fabrics and Film Association - Vinyl Roofing Division.
2. General: Zinc and its use in preventing moss and lichen from growing on roofs: information provided by Oregon State University's College of Science.
4. Shingles - Asphalt: "Algae & Moss Prevention and Cleaning for Asphalt Roofing Systems" provides basic information. Available at the ARMA website.
5. Shingles - Asphalt: "Algae Discoloration on Roofs" provides basic standard information. This short technical bulletin is available on the Canadian Asphalt Shingle Manufacturers' Association website.
6. Shingles - Wood: "Care and Maintenance of Wood Shingle and Shake Roofs" explains things pretty well. Available on Oregon State University's Pacific Northwest Plant Disease Management Handbook site.