Are algae-resistant shingles worth considering in Florida?

The Asphalt Roofing Manufacturers Association does not present algae-resistant shingles as something to add to a roof. It presents them as an option at one moment, the day a roof comes off and a new one goes on.

ARMA's technical bulletin on algae discoloration opens the subject with its condition: “When considering reroofing, several types of algae-resistant roofing shingles have been developed and are now commercially available.” The next sentence adds a second condition, that the roof “appears to be vulnerable to algae discoloration,” and only then uses the verb that matters, may consider. Both conditions come before the product.

The same bulletin explains why the question comes up at all. It says discoloration may be lightened with a solution of liquid household bleach (sodium hypochlorite) and water, and then limits that sentence at once: “The effectiveness of such cleaning is only temporary, and the discoloration may recur.” The algae-resistant shingle comes later in the same bulletin, as an option for when the roof is replaced. What the makers say about cleaning the shingle, tile and metal roofs already on a house is set out under what each roofing maker says about cleaning its roof type.

The product is an asphalt shingle, so the choice belongs to shingle roofs. ARMA says almost all types of roofing systems are susceptible to algae discoloration, and the separate question of whether roof algae damages tile has its own answer.

ARMA's condition is a roof that appears vulnerable, and its own bulletins say where that description fits most often.

ARMA writes that “Algae discoloration of roofs is most widespread in the Gulf States and along the Northwest and Eastern Seaboards” and that it occurs to varying degrees everywhere, especially where conditions are warm and humid. Its maintenance page on algae and moss adds: “Coastal or humid climates create the most conducive conditions for algae growth.” Florida is one of the Gulf States in that first sentence.

The organism behind most of it is Gloeocapsa magma, which ARMA calls “probably the most prevalent of several algae species that contribute to discoloration.” ARMA says its natural pigments may turn white or light-colored roofs dark brown or black, uniformly or in streaks, and that the most common type shields itself from ultraviolet rays with a dark pigmented sheath. That sheath is the dark color a neighbor sees from the street.

ARMA's sentence gives no measure of vulnerable, and neither do the maker pages quoted here. The climate reasons a roof here stains are argued in why algae seems to grow faster in Naples; this page stays with the shingle.

The two shingle makers quoted here describe the same idea in their own words, and both put the promise inside a limited warranty rather than on the label.

GAF's technical bulletin TAB-R-102 lists installing algae-resistant shingles as its first solution and describes its version as “engineered with thousands of microsites that release algae-fighting copper over time.” CertainTeed says its StreakFighter technology “employs numerous copper-containing granules” and gives the reason: “Copper possesses natural anti-algae properties.” How copper in a granule differs from copper fastened to a roof is taken up in whether copper strips keep a roof clean.

Neither maker stops at the chemistry. GAF says its StainGuard algae protection limited warranty is “available only on products sold in packages bearing the StainGuard” logo, and it sends readers elsewhere for the terms: “See GAF Shingle & Accessory Limited Warranty for complete coverage, restrictions, and qualifying products.” CertainTeed says its algae-resistant shingles carry a limited warranty against contamination from blue-green algae during the first years of the roof, for a length that depends on the product.

The documents describe what the shingles are designed to do and what the makers put in writing. None of them compares one roof's result against another's, and none tells a particular owner to buy one.

That leaves a reroofing decision with the people making it, which means the homeowner together with the roofing contractor who will install the roof and can show which products and warranty documents apply. ARMA's own verb is may consider, and a product choice for a new roof sits outside anything a cleaning decides.

An algae-resistant shingle is still an asphalt shingle once it is on, so ARMA's cleaning rules for shingle apply to it. ARMA says never to use a pressure washer on an asphalt shingle roof because it will cause granule loss, and that other cleaning chemicals or methods should not be used without the approval of the shingle manufacturer. Whether algae itself harms the shingle underneath is a different question, answered in does roof algae damage shingles.