You pull into the driveway and there they are. Dark streaks running down the roof, often worst on the slopes that get the least sun.
That isn’t dirt. It’s algae, and it does best on a roof that stays damp. That’s Evansville. Mean relative humidity here is 70.2%, and it runs highest in December and September (NOAA 1961-1990 records).
We clean roofs with a low-pressure soft wash. Never a pressure washer. Call or text (812) 664-6222 to book your free exterior evaluation.
Why we never pressure wash a roof
We never pressure wash or scrub shingles, because those granules matter. They shade the asphalt underneath. InterNACHI notes that their hold on the asphalt loosens as a roof weathers, and runoff carries them away (InterNACHI). On an aging roof, a pressure washer would only speed that up.
So we don’t blast and we don’t scrub. A roof needs a different approach than a driveway. We use low-pressure cleaning and treatment methods made for roofing materials, then rinse gently.
Want the surface-by-surface version, from shingles to brick to concrete? Read pressure washing vs soft washing.
What the streaks are, and what else grows up there
From the ground, the stain looks dark brown or black, and it’s easy to take for soot or dirt. It’s algae. And algae can grow back over time. That’s how a roof that was clean a few summers ago can go dark again.
Moss and lichen can show up too, mostly on slopes that stay shaded. Evansville has plenty of shade. A 2011 study put the city’s tree canopy at 26%, and the city’s goal is 40% (Evansville Living, 2020). Big trees over a house keep some roof slopes shady and slow to dry.
For more on the cause, see what causes black streaks on a roof.
Why we look before we wash
We evaluate the roof first, and we only recommend cleaning when it makes sense for that roof. If the dark patches turn out to be bare spots where the granules are gone, washing won’t help. That’s a roofer’s call, and we’ll say so.
Cleaning also comes before any treatment. If you’re thinking about roof protection or rejuvenation down the road, the roof gets cleaned first. Nothing goes on over algae.
What the day looks like
- Your part. Shut the windows, move cars out of the driveway if you can, and keep pets inside.
- What’s below the roof. Before we start, we look at what sits under the roof edge: shrubs, flower beds, the patio, the cars. We plan the rinse around them.
- The wash. We apply the cleaning solution at low pressure and give it time to work. No brushes. No brooms.
- The rinse. We rinse the roof gently with low-pressure water.
Cleaning can leave a roof slick. Please stay off the roof while we work.
How long a clean roof stays clean
Not forever, and we won’t pretend otherwise. Algae can come back, most of all on the shady slopes that stay damp after rain.
That’s why some owners add roof protection after a cleaning. It’s a water-repellent treatment we apply to help the roof stay clean longer. Once it’s on, we check it with a water-beading test. It won’t keep algae away for good, and we won’t tell you it will.
The rest of the house
Gray streaks under the gutters? A dark film creeping up a shady wall? We also do house and exterior washing for siding, brick, soffits and gutter faces. Driveways and walks too. One visit can cover the whole property.
You probably don’t need this if…
- A few faint streaks on a back slope don’t bother you. There’s no rush, and we’ll tell you if we think it can wait.
- You’re replacing the roof soon.
- The dark patches are bare spots, not stains. Missing granules are a roofer’s problem.
- You want it done with a pressure washer. We won’t do that to a roof.
- You want a roof that stays clean for good. Cleaning doesn’t do that, so we won’t promise it.
What happens next
Start with the free exterior evaluation. We look at the roof, tell you if cleaning is the right call, and show you photos of what we found. If it is, we set a date. If it isn’t, we tell you why.
Call or text (812) 664-6222. Terrance answers Monday to Saturday, 9am to 5pm.
Common questions
Will soft washing hurt my shingles?
We keep it gentle: low pressure, no brushes or brooms, and a soft rinse. So we keep high pressure and scrubbing off the roof. If we see loose or damaged shingles at the evaluation, we point them out before anyone cleans anything.
Can I clean my roof myself?
You can, but think it through first. A wet roof is slippery, and a fall from one is no small thing. Skip the power washer, brush and broom, because they knock granules loose. If you do it yourself, stay off a wet roof and save the pressure washer for the driveway.
Will the black streaks come back?
They can. Algae can grow back over time, especially where shade keeps a slope damp. A protection treatment after cleaning is meant to help the roof stay clean longer. It doesn’t make a roof algae-proof, and we won’t say it does.
Does roof cleaning make a roof last longer?
We won’t claim that. We haven’t seen a source that puts a number on what cleaning adds to a roof. What cleaning does do is take the algae off, so you and we can see the roof’s real condition. That matters if you’re deciding what comes next.