What you need to know about Roof Cleaning

cedar roof restoration
New roofs have about a 10 year resistance to algae, moss and lichen. Usually it is black algae (dark vertical streaks – aka Gloeocapsa Magma) that invades the roof surface, then moss and lichen move in after a ‘soil-load’ aka biofilm (think plaque) is established. If enough time has passed that a lot of lichen and moss is now present it would be best to restore your roof in two steps, not just one. 

Note: If you have only algae (black or green) consider yourself lucky – no damage has occurred to your roof – this can often be resolved in one day.

First, Algaecide is applied and allowed to sit for a week or more, and at least a month when thicker moss is present. In fact the longer the better! This allows the growths time to decompose naturally and for the roots to shrivel and loosen their grip on your roof.  I then return to remove the growths with my Soft Wash, a very low pressure approach. This method allows for a much longer lasting result. yes, it may cost a little more but it is well worth it – and I try to offset this extra cost by often including a complementary wash of your siding.

There are two other approaches to roof cleaning that require only one visit, but some education is warranted here.
1 – the contractor arrives and ‘blasts’ your roof with high pressure. This is damaging to your roof shingles as it removes grit and may create leaks.
2 – the contractor arrives and applies an algaecide that kills all the growths and removes the staining (black algae streaks), but does almost nothing to remove the soil-load/biofilm or the lichen and moss.

Note: Roof surface maintenance is not unlike Dental Care. We all know that mouthwash alone doesn’t make for complete oral hygiene, and that brushing and flossing are necessary (there is lots of documentation on this). It’s no different with roofs, siding, decks, or any other surface. Proper surface cleaning involves at least some physical scrubbing or mechanical agitation to remove the plaque and fertile substrate. I have seen many enterprises out there marketing products and approaches that they claim do not require rinsing. “Wet & Forget” solutions and other “No Rinse Roof Treatments” are good starts that will kill the growths but DO NOT remove the foundation which will then only invite regrowth in a very short time, sometimes in less than a year. Additionally a yearly application is recommended as long *as long as this soil load remains*. My approach removes both black algae/mold/mildew staining AND the soil load so that fertile conditions for future growths are eliminated. Remember, the principle function of using some pressure-washing is ‘soil load removal”.

Lichen eats roof grit! and it’s the gravel/grit layer on your shingles that protects the asphalt underlayer from the sun and gives beauty, durability to the structure of the whole shingle.
Below are examples of what Lichen can do if allowed to have it’s way with your roof.

Further Info at:  https://www.bobvila.com/articles/black-roof-stains-check-for-algae/