If your drive for spring cleaning demands a clean house
inside and out, you may wonder
what to do with those dirty shingles.
Before you pay high costs to replace your roof, try cleaning
it.
In high-humidity areas, roofs often turn dark brown or black
within five to seven years
because fungi and algae feed on dirt in shingles.
The fungus can start growing on a new roof right after the
first shingle is laid down,
says Dale Dorman, a housing specialist with the University of
Georgia Extension Service.
“The growth first appears as black streaks or wedge-
shaped areas that spread
across the roof,”> Dorman says. “After a few years,
the discolored areas
merge, and uniform discoloration eventually results.
“Fungus and algae growth is usually heaviest on west- or
north-facing roofs or on
those shaded by trees,” she says. “Dew dries more
slowly in these areas.”
The good news is that these stains don’t mar the roof’s
strength or service life.
Research at Mississippi State University found several chemicals
can remove shingle
discoloration caused by fungi, algae and lichen.
“One of the best cleaners is liquid household
bleach,” Dorman says. “And
it doesn’t damage the shingles.”
Apply a 75 percent solution of household bleach (three parts
bleach to one part water)
to asphalt shingles. Use one gallon of solution per 30 to 50
square feet of roof surface.
About 15 gallons of bleach will treat 1,000 square feet of
roofing.
“Roofs will remain clean for at least five years if
sprayed with the 75 percent
bleach solution,” Dorman says.
Cleaning power decreases with less bleach. A 10 percent
bleach solution will kill the
fungus, but it won’t clean the roof immediately. The dead
organisms will eventually wash
away with rain. But the roof will remain clean for only about a
year.
Clean your roof in strips starting at the peak and working
toward the eaves, Dorman
says.
“Treated roofs are slippery when wet, so work from a
ladder,” she says.
“Use a clean garden sprayer to apply the mixture.
“Avoid skin contact with the solution,” she says,
“and cover any shrubs
or plants below the eaves with plastic. Dilute any solution
reaching the ground by
spraying it with water.
If you have rain gutters at the eaves, remove all leaf
screening and place a garden
hose in the gutter. This will dilute the solution as it drips
from the roof. You don’t
need to scrub the roof or rinse off the solution.
“While cleaning the shingles, look for damage on your
roof,” Dorman says.
“Note cracks in the shingle surface, curling corners,
buckling front edges or loss of
granules.”
“If you have to reroof, use a fungus-resistant shingle
that carries a 20-year
limited warranty against fungus growth,” she says.
“The shingles release zinc
granules when it rains, destroying fungus and algae.”
The fungus-resistant shingles offer an inexpensive way to
maintain beauty, Dorman says.
