Algae Stains On Roof Shingles?
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Posted Wednesday, May 27, 2009 | 69 Views |
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Our roof shingles have algae stains that turn the roofing black. Is there anything to put on the roof that will kill the algae but not harm the shingles?
According to the Journal of Light Construction there is a method that will work. It is important that not only the proportion of the ingredients be correct but that due caution be taken to protect other surfaces.
The formula is three parts fresh Clorox bleach to one part water, to which is added half a cup of TSP (trisodium phosphate) or TSPPF (phosphate-free) per gallon. Spray it with a garden sprayer on the affected areas at the rate of one gallon per 50 square feet of roof.
This must be done with caution as this mixture will kill grass under the downspouts, any vegetation under the gutters and cause harm to the metal gutters. All plantings below the roof should be thoroughly wetted and covered with plastic. Water must be kept running in the metal gutters to dilute and wash away the solution as long as it is dripping into them.
Thoroughly rinse the plastic, the surrounding area, and any vegetation when you have finished spraying the roof. Don’t rinse the roof, however. It will take a few weeks before the algae stains are gone.
When cleaning a roof, care should be taken to minimize walking on or abrading the roof shingles. Cleaning a roof with bleach and TSP is effective but not permanent. In humid areas where roof algae is common, the algae may return as soon as one year after cleaning.
Source: Henri de Marne
February 2000 Issue Journal of Light Construction
Note:
If you have galvanized roof vents or galvanized pipe flashing, you may notice that the area directly below these items will not have near the algae growth. This is due to the zinc coating on the metal. Zinc has been found to help control algae growth. There is a product called “Z-Strip” that is a 3 inch wide strip, made from a zinc alloy, that can be installed along the top of the roof parallel to the ridge. These strips release zinc ions, which are carried down the roof by rainwater and helps to prevent the algae from growing. The average roof can be protected for around $80.00. If you are interested, you can contact the manufacturer for more information or place an order by contacting Wespac Enterprises, PO Box 46337, Seattle, Washington 98146 or