Roof Washing in St. Louis: Costs, Soft Washing, and Finding a Pro
Revised July 24, 2026
How should I clean my St. Louis roof?
In St. Louis, a roof should be soft washed — low pressure plus a cleaning solution that kills algae, moss, and lichen — not pressure washed, which strips the protective granules and can void your shingle warranty. The dark streaks are Gloeocapsa magma algae that thrives in humid Midwest summers. Professional cleaning usually costs $400–$600 and is worth doing about once a year, or whenever streaks return — it protects the roof and restores curb appeal for a fraction of a replacement.
Keep reading ↓You pull into the driveway, glance up, and there they are: dark streaks running down the roof like the house hasn’t been cared for in years. Maybe a patch of green fuzz in the shady spots, too. It nags at you every time you come home.
If that’s you, good news — that gunk usually cleans right off, and getting it done protects your roof at the same time. Here’s a St. Louis guide to roof washing: why it happens here, when to do it, what it should cost, and how to pick someone who won’t wreck your shingles in the process.
Why St. Louis roofs get those black streaks
Those streaks are almost always a hardy blue-green algae called Gloeocapsa magma, and it loves our hot, humid Midwest summers. It feeds on the crushed limestone filler baked into asphalt shingles, and it spreads fastest across the north- and shade-facing slopes that stay damp the longest after a rain. St. Louis gives it just about everything it wants: sticky July humidity, plenty of mature tree canopy dripping shade and spores onto roofs, and the freeze-thaw swings that keep shingles a little porous.
Left alone, the algae mat traps moisture against the roof, and that trapped moisture — not the color — is what quietly shortens a roof’s life. So the streaks aren’t just an eyesore; they’re a slow-motion maintenance problem. Moss and lichen do the same thing in the shadiest, dampest corners, and because they root into the shingle surface, they can lift and separate granules over time.
Signs your roof is due for a wash
- Dark streaks or stains, especially obvious after rain — that’s the algae.
- Fuzzy green moss or crusty, colorful lichen in shaded areas — these hold moisture against the shingles and dig in.
- Gutters that keep clogging with grit and black debris — often shingle granules and buildup washing down off the roof.
- A general weathered, dingy look that wasn’t there a couple of years ago, or one slope that looks noticeably darker than the rest.
If your neighbor’s roof looks streaky and yours faces the same direction, odds are yours is headed the same way — algae spreads spore by spore down a block.
Soft washing, not pressure washing
Here’s the single most important thing to know: a roof should be soft washed, not pressure washed. Soft washing uses low pressure — about what a garden hose puts out — paired with cleaning solutions that actually kill the algae, moss, and mold at the root and let it rinse away over the following days. It’s effective, and, crucially, it doesn’t blast off the protective granules the way high pressure does.
The solution most pros use is a measured mix of sodium hypochlorite (the active ingredient in household bleach), water, and a surfactant that helps it cling and penetrate. A good crew dilutes it correctly, lets it dwell, and thoroughly rinses your plants and soaks the landscaping before and after so runoff doesn’t burn the garden. If a company wants to power-wash your whole shingle roof, get a second opinion — high pressure can void your shingle warranty and take years off the roof in a single afternoon. The major shingle manufacturers and the roofing-industry association (ARMA) specifically recommend low-pressure cleaning for exactly this reason.
Different roofs, different rules
Most St. Louis homes wear asphalt shingles, and everything above applies to them. But if you have a different roof, the approach changes: cedar shake needs gentler, specialized treatment; clay or concrete tile can be walked and cleaned but cracks if handled carelessly; and metal roofs usually just need a mild wash. Tell whoever you call what kind of roof you have — a pro who only knows one method is a red flag.
How to choose a roof washer
- Experience and a local track record — this is height work on a delicate surface; you want people who’ve done a lot of it on St. Louis homes.
- Licensing and liability insurance — ask for proof, and don’t just take their word for it. If someone is hurt on your roof or your siding gets damaged, you don’t want to be the one on the hook.
- Reviews and references — recent, local, and consistent. Before-and-after photos of real jobs tell you a lot.
- A written estimate and a workmanship guarantee — get the scope and price in writing, and confidence that they’ll come back if a spot needs a touch-up.
- The soft-wash method, in their own words — ask how they’ll clean it. If the answer is “pressure washer,” keep calling.
One St. Louis-specific caution: after a big storm rolls through, out-of-town crews go door to door offering cheap cleanings and quick roof “inspections.” Stick with established local companies you can look up, and never pay in full up front.
What it costs and how often
Professional roof cleaning commonly runs a few hundred dollars — national figures cluster around the $400–$600 range — depending on your roof’s size, pitch, how much growth there is, and how easy it is to access. A steep, cut-up roof with heavy moss costs more than a simple ranch with light streaking. Always get a local quote for your specific roof rather than trusting a flat number.
For most St. Louis homes, a wash about once a year — or whenever the streaks and moss start coming back — keeps the roof healthy and the curb appeal high. Heavily shaded, tree-covered lots may need it a little more often; a sunny, wind-dried roof can go longer. Either way, it’s a tiny fraction of what a premature roof replacement costs, and some shingle warranties actually require reasonable maintenance like this to stay valid.
When to schedule it
Spring and fall are the sweet spots in St. Louis — mild, dry stretches let the solution dwell and rinse properly, and you avoid both the peak-summer heat and hard freezes. Cleaning going into fall also clears growth before the damp, shorter days when moss really digs in. Pros book up in nice weather, so call a week or two ahead rather than the day you finally get fed up with the streaks.
Should you DIY it?
Tempting, but think twice. Roof work means ladders, steep and slick surfaces, and cleaning chemicals — and a misstep can hurt you or damage the roof. Falls from ladders are one of the most common serious home-improvement injuries, and getting the bleach mix wrong can streak siding, kill plants, or leave the algae half-alive so it’s back in months. For most homeowners, hiring a pro who already has the gear, the insurance, and the soft-wash know-how is the safer, smarter call. If you do tackle light spots yourself, work from a ladder at the edge — never walk a wet, treated roof.
What a soft-wash visit actually looks like
Knowing the routine helps you spot a pro from a hack. A good crew starts with a quick look at the roof and the surrounding landscaping, then wets down and covers nearby plants and shrubs so nothing gets scorched by runoff. They apply the cleaning solution at low pressure from a ladder or with an extension setup — often without walking the roof at all — and let it dwell for several minutes so it kills the algae and moss at the root. Then they rinse gently and give the plants another soak. Most single-family roofs take somewhere between one and three hours. You may still see faint shadows on day one; the roof keeps clearing over the next few rains as the dead growth washes away, which is normal and a sign the treatment worked. If a company shows up with nothing but a pressure washer and starts blasting from the peak, that’s your cue to stop them.
Roof washing vs. a new roof
Cleaning solves an algae-and-moss problem; it doesn’t fix a worn-out roof. If your shingles are curling at the edges, going bald in patches, cracking, or you’re finding granules by the handful in the gutters, those are signs of age, not just growth — and a wash won’t buy you much. The same goes for any active leak or soft, spongy decking. In those cases you want a roofer for an honest inspection, not a cleaner. The sweet spot for roof washing is a structurally sound roof with a cosmetic and biological problem: streaks, moss, and lichen on shingles that still have plenty of life left. Done at the right time, a wash can genuinely add years by stopping moisture damage before it starts — but it’s maintenance, not a substitute for a replacement a roof has already earned.
Curb appeal, resale, and the rest of the exterior
If you’re thinking about selling, a clean roof is one of the cheapest ways to sharpen a first impression — buyers (and their agents) read dark streaks as “deferred maintenance” and start wondering what else was let go, even when the roof is fine. A wash resets that impression for a few hundred dollars instead of a five-figure replacement. It’s also worth thinking of the roof as one part of the whole exterior: the same soft-wash crews usually clean siding, brick, soffits, and fences, and many St. Louis homes with a streaky roof have green-tinged north-side siding to match. Bundling the house and roof in one visit often costs less than booking them separately, and it gets the whole place looking cared-for at once — which is exactly the signal you want to send whether you’re selling or just tired of the streaks nagging at you every time you pull in.
Find a pro
Ready to clear those streaks? Browse the Home Services listings in the St Louis Near Me Directory to find roof and exterior-cleaning pros across the metro, compare reviews, and reach out before the algae spreads any further.
Tackling other projects? See our step-by-step home repair guide.
Ready to clear those streaks? Browse the St Louis Near Me home services directory to compare roof and exterior-cleaning pros across the metro.
If you run a roof-washing or pressure-washing business, listing it is how homeowners find you when they search “roof washing near me” — or start with a free AI-visibility check to see how visible you are right now.
Frequently Asked Questions
Why does my St. Louis roof have black streaks?
They’re caused by algae (Gloeocapsa magma) that thrives in hot, humid summers and feeds on asphalt shingles, spreading on the shaded, slower-to-dry slopes. It traps moisture against the roof, so it’s worth removing before it shortens your roof’s life.
Is pressure washing bad for a roof?
For most shingle roofs, yes — high pressure can strip the protective granules and even void your warranty. Professionals use low-pressure “soft washing” with cleaning solutions instead, which kills the growth at the root and removes it safely.
How often should I have my roof washed in St. Louis?
About once a year, or whenever the streaks and moss return. Our humid summers and heavy tree cover encourage regrowth, so an annual soft wash keeps the roof healthy and looking sharp. Shadier lots may need it a bit more often.
How much does roof washing cost in St. Louis?
Most professional roof cleanings run in the $400–$600 range, depending on the roof’s size, pitch, access, and how much algae or moss has built up. Get a quote for your specific roof — it’s a small fraction of the cost of replacing a roof early.
Will roof washing damage my shingles?
Not when it’s done with the soft-wash method — low pressure plus a cleaning solution rinses the growth away without stripping granules. Damage comes from high-pressure washing or from letting moss and algae sit for years, not from a proper cleaning.
How long until my roof looks clean after a soft wash?
Some streaks lift right away, but a soft wash keeps working over the following days and rains as the dead algae and moss wash off. Most roofs look noticeably better within a day and fully clear over a week or two, which is normal — the solution is designed to kill the growth at the root, not just rinse the surface.
Written by a dedicated team of St. Louis locals who live, work, and play right here in the St. Louis metro. Founder Lane Forman and team are committed to building the region’s most trusted directory by verifying listings and connecting local businesses with loyal customers across Missouri and Illinois.