Each method has its advantages and disadvantages.
A chlorine and water solution can be used followed by a thorough rinse. Of course, since chlorine can be toxic to people and plants, proper care should be taken to protect employees and the surrounding property from overspray and runoff. The benefits to using chlorine include a much faster cleaning process and minimal rinsing as compared to other methods. This translates into much less wear & tear - particularly asphalt shingle roofs.
Sodium Hydroxide based cleaners are generally advertised as safer for the landscaping, but sodium hydroxide is caustic, very toxic, and care should also be used to protect employees and surrounding property. Sodium hydroxide is also a very effective degreaser. So high levels of sodium hydroxide in a cleaning product can cause irreversible damage to an asphalt shingle roof. In addition, these products generally require much more rinsing than the chlorine method. The rinsing process is not only time consuming, but it can also be potentially damaging to the roof if not done correctly. A quality sodium hydroxide based product should not require any more than 100 psi to effectively rinse - and even then some granule loss should be expected.
Pressure cleaning is an option that should only be used on concrete, barrel tile, or metal. Pressure cleaning has the advantage of not requiring chemicals, which eliminates most of the landscaping and chemical exposure concerns.
The down side to pressure cleaning is that it is very time consuming and it exerts tremendous force on a surface that is not really designed to handle it. In addition, repeated pressure cleaning can wear away the surface of some tiles that are only covered by a thin layer of coloring. When this happens, the gray concrete color starts to show through and the roof must be stained or painted.
Authorized Roof-A-Cide® Applicators can clean safely using our Roof-Restore™ formula. Roof-Restore™ is a revolutionary new cleaning formula that contains no chlorine bleach, sodium hydroxide, or other harsh chemicals. Roof-Restore™ requires only minimal rinsing - so it is safer for the granules on your shingles as well.