Why would I want to clean my roof?
So you might say "Why would I want to clean my roof? That's the way a roof is supposed to look...right?. Why "waste" the money?" Well, there a couple of reasons why it is important to clean a slate roof. The first reason is that it simply looks fresh and bright but the most important reason is Winter Weather in New England. Almost without exception, slate problems occur where snow, moss or algae has lain on the slate surface for prolonged periods. In cases where trees are not hanging over a roof, the surface is problem free (trees create a fertile environment beneath them that fosters moss, algae and lichen growth which holds moisture and snow in place). In winter as the daytime sun melts some of the snow, the water falls into the slate through fissures and cracks and absorbs into the slate. At night it freezes and expands, widening the cracks and pores, providing larger cavities for the next days melting water. The cycle continues with tremendous expansion and contraction of the slate around the cracks. A once strong and solid surface has become broken and flakey. This situation will requires expensive repair or replacement. The best way to eliminate or reduce this problem is to eliminate the algae, moss and fungus.
Important Note: Proper surface cleaning involves either physical scrubbing or some level of pressure to remove the plaque and fertile substrate. There are several enterprises out there marketing products that they claim do not require rinsing. "Spray and Forget" and other "No Rinse Roof Treatments" are good starts but do not remove the foundation which will only invite regrowth in a very short time, sometimes in only a few months. We all know that mouthwash alone doesn't make for healthy oral hygiene, and that brushing and flossing are necessary. It's no different with roofs, siding, decks, or any other surface. There is lots of documentation on this. Common sense also works.
Lichen will completely digest the silica grit, exposing bare asphalt. This will not be so visible on a darker shingle. It is important the silica granules remain on an asphalt shingle roof so that they can do the job of reflecting the sun's rays. Use of proper cleansers and a low pressure rinse will ensure that your silica granules remain intact.
There was enough lichen and moss on this 25 year old cedar shake roof....
to support a habitat for tree frogs. Once restored, this roof looks nearly new even after all these years. This is mostly due to two factors. One; the lack of strong sun at the location of this particular home and two; these shingles were handsplit tapered shakes. Nothing really can compare to these. They will absorb a lot of abuse. Nonetheless, there were some rotting on the edges
If we all lived on Nantucket...
...the airborne sea salt would cure and preserve the cedar shingles for us, which would prevent wet rot.
Cleaning Asphalt Shingles
Cleaning an asphalt roof involves proper detergents and very low pressure. Without the proper solutions the novice is prone to rely too much on pressure alone, which will damage the shingle by removing the grit.
Shingle Shield has some effectiveness
The maintenance free roof protector. Protect the appearance of that new, or just cleaned roof with Shingle Shield Roof Protector zinc strips. These strips are engineered to provide long term protection from fungus, moss, and algae. Simply install one row at or near the roof ridge line to protect the entire roof. Shingle Shield zinc strips react with rain water to release powerful, non-toxic, fungistatic compounds of zinc oxide. For best results, thoroughly clean and disinfect the roof prior to installing zinc strips. 20+ years is the expected period of protection.