In 1993, three of the 14 U.S. asphalt shingle manufacturers
listed in the first edition of NRCA's Steep-slope Roofing Materials
Guide offered algae-resistant shingles. Algae-resistant shingles
filled a niche in the steep-slope roofing market, appealing to
roofing contractors and consumers located in hot, humid areas of
the U.S. Availability typically was restricted to the Southeastern
and Gulf of Mexico coastal regions of the U.S.
Presently, nine manufacturers supply asphalt shingles to the
U.S. roofing market. Eight of them offer a variety of
algae-resistant shingle products that are readily available
throughout the U.S. and Canada.
The growth of algae-resistant-labeled asphalt shingle sales can
be interpreted as an indication the steep-slope roofing market is
receiving products that provide effective protection against
unsightly microbial discoloration. That, in essence, is the
position of asphalt shingle manufacturers. Asphalt shingle
manufacturers and algae-resistant system suppliers say this claim
is based on evidence collected from long-term product exposure in
weathering farms and positive feedback about product
All asphalt shingle manufacturers that currently offer
algae-resistant shingle products assert they possess empirical
data—or have access to algae-resistant granule suppliers'
long-term shingle exposure results—that support claims about
the performance of their respective products. This evidence is not
available to the public. In addition, no recognized standard is
available for objective evaluation of long-term resistance to
microbial staining of roof...
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