Roof washing for shingles streaked black
Those dark streaks running down the north slope are almost always algae. They come off with a soft wash, and they should never be pressure-washed.
What the streaks are
Most dark streaks on East Tennessee roofs are a blue-green algae (often called gloeocapsa) that feeds on the limestone filler in asphalt shingles. It spreads downhill with rain, which is why the stains run in stripes from the ridge. Moss and lichen grow in the shadiest spots, often under overhanging trees. All three hold moisture against the shingles and shorten their life.
Why we never pressure-wash a shingle roof
The colored granules on a shingle are what protect the asphalt from the sun. High pressure knocks them loose, and many shingle makers say in their warranty terms that pressure washing voids coverage. So a roof gets a soft wash only: the solution goes on from a ladder or the gutter line, sits long enough to kill the growth, and is rinsed gently or left for rain to finish, depending on the mix and the roof.
Metal roofs
Painted metal roofs handle a gentle rinse better than shingles, but the paint finish can still be scarred by a close, narrow spray. Same method, lower strength solution.
What to expect
- Streaks usually fade the same day; heavy lichen can take a few rains to release fully.
- Gutters and downspouts get flushed afterward so the runoff doesn't sit in them.
- Plants under the drip line are soaked before and after.
- Nobody walks a steep or wet roof; access is from ladders and the eaves wherever possible.
Roof repair is a different trade. If the wash turns up lifted or missing shingles, you'll get photos, but we don't do roof repairs.
Asked about roof washing
Still wondering about something? Call (865) 390-6589 and ask. It costs nothing to ask.
How long does a roof stay clean after a soft wash?
Often several years, depending on shade and overhanging trees. A roof under big oaks will grow back sooner than one in full sun.
Will roof washing void my shingle warranty?
Pressure washing can, by many manufacturers' terms. A low-pressure soft wash is the method roofing makers generally point to, but check your own warranty paperwork if it matters to you.
Do you install zinc or copper strips?
No. Those are installed by roofers. We wash the roof and can tell you which slopes regrow fastest.