What the black streaks are
Gloeocapsa magma spreads by spores on the wind, and once it lands on a damp shingle it grows a dark protective coating to shield itself from the sun. That coating is the streak. It starts on the north slope and the shaded side under oaks and pines, because that is where the roof stays wet longest, then spreads. The humidity off the Black Warrior River and Lake Tuscaloosa gives it plenty to work with. Lichen and moss follow later on roofs that have been streaked for years, and those take more work to lift.
The streaks do not rinse off in rain and they do not scrub off. The algae has to be killed, and then the dead growth lets go on its own over the following weeks of weather.
Newer shingles sold as algae-resistant have copper granules mixed in, and they do slow the streaking down, but on a shaded slope in this climate they streak eventually too. A roof installed in the last few years with streaks already showing is not a defective roof; it is a Tuscaloosa roof that faces north under a pine.
Why we never pressure wash shingles
An asphalt shingle is a fiberglass mat coated in asphalt and covered in mineral granules. The granules are the roof. They block UV, shed water and give the shingle its color. A pressure wand knocks them loose by the handful and the roof looks bald in the places that got hit hardest. Pressure also lifts the shingle edge and drives water under it, which is how a cleaning turns into a leak.
So the roof gets the low-pressure rinse we use on siding, with a stronger solution. We apply it, let it sit, and rinse what needs rinsing. Most of the time the streaks fade partway during the job and finish fading over the next few rains.
Metal, tile and shingle roofs
Asphalt shingle is most of what we clean. Metal roofs, common on newer houses in Coker and out toward the Brookwood side of the county, grow the same algae and mildew along with pollen film in the ribs. They get a lighter mix and a careful rinse so nothing streaks on the finish. Concrete and clay tile hold algae in the texture and in the overlaps; they get soft washed too, and we walk tile as little as possible because it breaks.
Cedar shake is a different conversation and depends on its condition. Ask and we will look at it.
Whatever the roof is made of, the flashing, the vent boots and the skylights come along for the wash. We check them while we are up there and tell you if a boot is cracked or a skylight seal has failed, because that is easier to hear from us on a dry day than to find out during a storm.
What a roof wash day looks like
We work from a ladder at the gutter line or from the roof itself when the pitch allows. Plants and lawn below the drip line get soaked with water first. The solution goes on in sections, bottom of the slope up, and we watch the runoff the entire time. Gutters get flushed when we are done so the solution does not sit in them. Then plants get rinsed again.
A typical one-story roof takes a few hours. Two stories, steep pitch or heavy lichen add to it. You do not need to be home, but if you have a rain barrel or a cistern fed by the downspouts, disconnect it or tell us so we can. We work Monday through Saturday, 7am to 6pm, and answer quote requests the same day.
Gutters and the landscaping
The runoff from a roof wash goes into the gutters, so we flush them, and if they are packed with pine straw and oak leaves we can clear them while the ladder is up as a combined job. Downspouts that dump onto a flower bed get a hose or a diverter for the day. Anything the solution would touch gets covered or rinsed. The boxwoods under the eaves of a brick ranch in Alberta have come through this hundreds of times without a brown leaf.
Related
House Washing
Low-pressure soft wash that lifts algae, mildew and pollen film and keeps water out of the wall.
Questions we get
Will the streaks be gone the same day?
Most of them. The algae dies on the day and the dark coating fades and washes away in the rain over the following few weeks. Heavy streaks sometimes take a month to disappear fully.
Does roof cleaning void a shingle warranty?
Pressure washing can. A low-pressure wash with the chemistry shingle makers specify does not, and it is the method they recommend for algae.
How long before the streaks come back?
Several years on most Tuscaloosa roofs. Shaded north slopes under oaks and pines come back sooner than open, sunny ones.
Can you clean a roof with solar panels?
We clean around them and keep the solution off the panels. The panels themselves are a separate job.
Do I need to be home for a roof wash?
No. We need the outside water on, the cars moved out from under the drip line, and a heads-up about any rain barrel or pet in the yard. Everything else happens outside.