You pulled into your driveway this morning, looked up, and finally admitted it: the dark streaks on the north side of your roof have gotten worse. Maybe they started near the chimney. Maybe they ran down from a single shingle and now stretch across half the slope. Either way, you’ve reached the part of homeownership where the question stops being is it really that bad? and becomes what is that, and how do I get rid of it?
You’re not alone. We get this call from Austin homeowners every week — from South Austin bungalows to two-story homes in Lakeway, Westlake, and Round Rock. The streaks look like dirt or soot, but they aren’t. They’re a living organism. And the way most people instinctively want to fix the problem — climb up there with a pressure washer — is exactly the wrong move.
This guide walks you through what’s actually growing on your roof, why Austin’s climate makes it worse, why pressure washing voids your shingle warranty, and what a real roof cleaning looks like when it’s done the manufacturer-approved way.
The dark streaks are colonies of a cyanobacterium called Gloeocapsa magma. Despite the nickname “roof algae,” it’s technically a photosynthesizing bacteria — and it has a very specific food source: the powdered limestone (calcium carbonate) used as a filler in modern asphalt shingles.
That’s why the problem is relatively new. Older shingles didn’t contain limestone in the same way, so they didn’t feed the bacteria. The streaks you’re seeing on your roof exist because the shingles are, quite literally, on the menu.
Once a colony establishes itself, it produces a dark, UV-resistant outer sheath to protect itself from the sun. That sheath is what you see streaking down your roof. Rain doesn’t wash it off — it spreads it, which is why the streaks always run downward and why your north and west-facing slopes (the shaded, slower-to-dry sides) are usually the worst.
Three different organisms colonize Austin roofs, and they need slightly different treatments:
A proper soft wash kills all three at the root using the same solution. The difference is dwell time and whether a second pass is needed for lichen.
If you’ve lived in the Northeast or Pacific Northwest, you’ve seen worse roof staining. But Austin has its own perfect storm — and it’s getting worse, not better, as the city densifies and tree canopies mature.
Three local factors stack the deck against your shingles:
Algae needs moisture to grow, and Austin’s average relative humidity sits around 65–75% for most of the year. That’s not Houston-level swamp, but it’s plenty for cyanobacteria — especially in spring and fall when overnight dew sits on shingles for hours.
Austin’s beautiful tree canopy is also a roof’s worst enemy. Heavy shade keeps the north and east slopes damp longer after rain, and falling debris — pollen, oak catkins, cedar fronds — drops organic matter directly onto the roof surface. That debris feeds moss and creates micro-environments where moisture can’t evaporate.
The vast majority of Austin homes have three-tab or architectural asphalt shingles, which contain the limestone filler that Gloeocapsa magma feeds on. Metal, tile, and slate roofs (which we also clean, with adjusted chemistry) are far less hospitable to the same growth.
Combine these and you get the streaks you see today: not because your roof is failing, but because Austin’s climate is doing exactly what it always does, and your shingles are doing exactly what they’re designed to do.
Your roof isn’t dirty. It’s being eaten. The fix isn’t more pressure — it’s the right chemistry.
It would be one thing if the streaks were ugly and that was the end of it. They’re not. There are four real costs to leaving roof algae untreated, and three of them affect your wallet long before you replace the roof.
As Gloeocapsa magma feeds on shingle filler, it accelerates granule loss. The granules are what protect the asphalt mat below from UV, and once they’re gone, deterioration speeds up dramatically. Industry data and roofing manufacturers consistently report that untreated roof algae can shave 5 to 10 years off a roof’s usable life.
Dark streaks absorb more solar radiation than clean shingles. In Austin, where summer attic temperatures already crack 130°F, a streaked roof can run 10 to 15 degrees hotter than a clean one. That’s load your AC has to fight every August afternoon, and it shows up on your Austin Energy bill.
Some homeowners insurance policies — especially in Texas — now include “roof condition” inspections. Visible biological growth has been used as grounds for non-renewal or higher premiums. Separately, many shingle manufacturer warranties (GAF, Owens Corning, CertainTeed) require that roofs be kept reasonably free of algae and that any cleaning be performed in line with ARMA (Asphalt Roofing Manufacturers Association) guidelines. Pressure washing the roof is the fastest way to void that warranty.
If you’re considering selling — and right now plenty of Austin homeowners are — buyers and inspectors absolutely notice a streaked roof. It signals deferred maintenance even when the roof itself is structurally fine. A $500 cleaning can prevent a $5,000 negotiation hit at closing.
This is the part of the guide we wish every Austin homeowner read before climbing a ladder. Pressure washing an asphalt shingle roof is one of the most expensive mistakes you can make as a homeowner. It looks like it works for the first ten minutes — the streaks visibly disappear. Then over the next 12 to 24 months, the roof ages five years.
Here’s why:
High-pressure water blasts the protective granules off the shingle surface — the same granules that block UV, shed water, and give the shingle most of its lifespan. You can’t see the damage right after the wash. You see it the next summer, when the roof starts looking faded, brittle, and uneven.
The Asphalt Roofing Manufacturers Association (ARMA) and major shingle brands explicitly warn against pressure washing asphalt shingles. So do most warranty documents.
The right method is called soft washing. It uses very low pressure (under 100 PSI — about the same as a garden hose with a thumb over it) combined with a properly diluted sodium hypochlorite-based cleaning solution. The chemistry does the work, not the pressure.
A proper soft wash roof cleaning isn’t a “spray and walk away” job. Done right, it’s a five-step process that takes a small crew between 90 minutes and three hours depending on the roof. Here’s exactly what should happen on your property.
Before any solution gets mixed, the crew walks the perimeter and identifies damaged or lifted shingles, exposed nail heads, soft spots, and existing leaks. We also locate every plant, shrub, and grass area that needs protection.
This is where most untrained crews fail. Sodium hypochlorite is hard on plants if it’s allowed to dry on foliage. The right approach: pre-saturate every plant within drip range with fresh water, cover sensitive items with tarps where needed, and run a slow constant rinse on landscaping during application. We don’t lose plants and neither should you.
The cleaning solution — a properly diluted blend of sodium hypochlorite, surfactants, and water — is applied with a soft wash pump at very low pressure. The crew works from the ridge down, in even passes, with no foot traffic on shingles that can be cleaned from a ladder or extension wand.
The solution sits on the roof for 10 to 20 minutes. This is the part that actually kills the algae. Skipping or rushing this step is why amateur jobs fade fast.
The roof gets a gentle low-pressure rinse, gutters get checked, and every square foot of landscaping gets a final saturating rinse with fresh water. The driveway and walkways get rinsed too — runoff can leave temporary marks if it sits.
Two important notes about results:
Soft wash roof cleaning prices in the Austin metro vary based on roof square footage, pitch, height, accessibility, and how aggressive the growth is. Here’s a realistic range based on what we and other reputable Austin crews charge in 2026:
Two things to watch out for when comparing quotes:
One of the upsides of doing roof cleaning the right way: you don’t need to do it often.
For most Central Texas homes, every 2 to 4 years is the right cadence. Heavily shaded properties — especially under mature live oaks or pecans — usually land closer to every 18 to 24 months. Homes with full sun exposure on metal roofs may go 5+ years between services.
The right cadence for your specific roof depends on shade, slope, debris load, and humidity exposure. We’ll tell you honestly during your quote — if your roof doesn’t need cleaning yet, we’ll say so.
Spring (March through May) and fall (September through November) are ideal in Austin. Temperatures are mild enough that the cleaning solution doesn’t flash-dry on the shingles, and the roof dries evenly afterward. We work year-round, but if you’re scheduling a one-time clean, those windows produce the cleanest results.
If you’re already planning a house wash this spring, bundling the roof clean with it is the move. Same crew, same trip, lower combined price, and the whole exterior matches when they finish.
Roof cleaning is one of those services where the bad jobs are nearly invisible until it’s too late. By the time you notice premature granule loss or a flashing leak, the crew that did it is long gone. Six things to ask before you hire anyone — including us:
For everything we do beyond roofs — house washing, driveway cleaning, gutter clearing, fence and siding restoration, car detailing — head over to our services page. If you’d rather just talk to someone, the number’s at the top of every page and we always pick up.
They’re colonies of a cyanobacteria called Gloeocapsa magma. It eats the limestone filler in asphalt shingles and produces a dark, UV-protective coating that creates the streaked appearance. It’s biological growth, not dirt or staining, and won’t wash off with rain alone.
No — and please don’t try. Pressure washing strips the protective granules off asphalt shingles, voids most manufacturer warranties, and dramatically shortens roof lifespan. The Asphalt Roofing Manufacturers Association and major brands like GAF and Owens Corning specifically recommend a low-pressure soft wash with a sodium hypochlorite-based solution instead.
Soft wash roof cleaning in Austin typically runs $375 to $850 for a standard single-story home and $600 to $1,400+ for two-story or steep-pitch roofs. Cost depends on roof square footage, pitch, accessibility, height, and severity of growth. We provide free, on-site quotes with no high-pressure sales.
Most Central Texas roofs benefit from a soft wash every 2 to 4 years. Heavily shaded homes — especially under live oaks or pecans — may need cleaning every 18 to 24 months. A quality soft wash kills the algae at the root, so results last far longer than a quick rinse.
Not when it’s done correctly. A professional crew pre-saturates plants and grass with fresh water, uses tarps where needed, and rinses thoroughly during and after the application. We treat every property like our own and guarantee no plant damage.
Yes. Algae actively consumes the limestone filler in asphalt shingles, accelerating granule loss and breakdown. Removing it can add 5 to 10 years to a roof’s usable life and lowers attic temperatures, since dark streaks absorb more solar heat than clean shingles.
Spring (March to May) and fall (September to November) are ideal — temperatures are mild, the roof dries evenly, and you avoid peak summer heat which can flash-dry cleaning solution. That said, an experienced crew can clean roofs safely year-round in Austin’s climate.
Free on-site quote, manufacturer-approved soft wash, fully insured. Serving Austin, Round Rock, Cedar Park, Pflugerville, Lakeway, Westlake, Bee Cave, and surrounding communities.
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