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I'm sure this is old news to those who have been doing this a long time but for us new guys; well, it might be something helpful to use when meeting with future clients.  Below is the ARMA Bulletin explaining how to clean roofs and it's essentially how we do it.  Next time just hand the customer a copy and say this is what we do and our price to do it is $$$$$.  Anyhow, I have it in a professional pdf layout if anyone wants a copy.  I'll try to upload and maybe you can download.  Have a great evening.

technical

bulletin

Asphalt Roofing

Manufacturers Association

1156 15th St., NW, Ste. 900

Washington, DC 20005

Tel: (202) 207-0917 • Fax: (202) 223-9741

www.asphaltroofing.org

A member service provided by the Asphalt Roofing Manufacturers Association

Revised May 2007

contained herein is intended to revoke or change the requirements or specifications of the individual roofing material manufacturers or local, state and

federal building officials that have jurisdiction in your area. Any question, or inquiry, as to the requirements or specifications of a manufacturer, should be

directed to the roofing manufacturer concerned. THE USER IS RESPONSIBLE FOR ASSURING COMPLIANCE WITH ALL APPLICABLE LAWS AND REGULATIONS.

Nothing contained herein shall be interpreted as a warranty by ARMA, either express or implied, including but not limited to the implied warranties of

merchantability, fitness for a particular purpose or non-infringement. IN NO EVENT SHALL ARMA BE LIABLE FOR ANY DAMAGES WHATSOEVER, including

special, indirect, consequential or incidental damages or damages for loss of profits, revenue, use or data, whether claimed in contract, tort or otherwise.

Where exclusion of implied warranties is not allowed, ARMA’s liability shall be limited to the minimum scope and period permitted by law.

For many years, roof discoloration caused by algae has been observed throughout the United States and Canada.

This is commonly referred to as “fungus growth.” The discoloration usually has a brown to black appearance, and

may be mistaken for soot, dirt, moss, or tree droppings.

The primary species of algae being observed is Gloeocapsa Magma. This type of algae is contained in and transported

through the air, and tends to collect and grow upon roofing structures. Natural pigments produced by this

algae may cause a white or light colored roof to gradually turn dark brown or black. The algae discolorations should

not be confused with moss or tree droppings, which typically produce only localized discolorations.

This type of roof discoloration has been most widespread in the Gulf States and along the Northwest and Eastern

Seaboards. It is not, however, confined to only these regions. Algae growth occurs to varying degrees in all regions

of the country, especially those subjected to warm, humid conditions. It should be noted that almost all types of

roofing systems are susceptible to algae discoloration. It is, of course, most readily visible upon white or pastel roofs,

while it is not so visible upon darker shades of roofing.

Algae discolorations are difficult to remove from roofing surfaces, but may be lightened by applying a solution of

chlorine bleach, trisodium phosphate, and water. Solutions for these ingredients may vary between shingle manufacturers

and depend on the amount of discoloration. Solutions range from one cup TSP, one gallon bleach and five

gallons of water, to one cup TSP and 2.5 gallons each of bleach and water.

First, gently disperse this solution on the roofing surface. Use normal precautions for handling bleach. Be sure to

apply it carefully to avoid damage to other parts of the building and its surrounding landscape. Avoid scrubbing the

surface, as this friction may loosen and remove granules. If possible, always work from a latter and/or walkboards to

avoid direct contact with the roof surface. Observe all possible safety precautions when working on or near the roof.

Finally, rinse the solution from the roof by gently spraying the surface with water. Be warned that this solution application

and rinse process will make the roof surface slippery and potentially hazardous to walk on during treatment.

The effectiveness of such cleaning techniques are only temporary, and discoloration will likely recur. However,

several types of algae resistant roofing products have been developed, and are now commercially available. These

asphalt roofing products are specifically designed to inhibit algae growth for extended periods of time.

High pressure washing systems for algae removal should not be used.