How to Remove Mildew From a House Exterior in Florida

How to remove mildew from house exterior surfaces in Florida almost always comes down to one method: a soft wash, not a pressure washer. Homeowners in Ponte Vedra, St. Johns, and the Jacksonville Beaches usually pay $200 to $600 for a whole-house soft wash, or $2 to $8 per square foot for stucco and roof-specific treatments where staining has set in. If you've noticed dark green-black streaks creeping across your siding, stucco, or roofline, you're not imagining it getting worse every summer — you're watching algae and mildew do exactly what Florida's climate lets them do best.

This guide covers what's actually growing on your house, why a pressure washer can make it worse instead of better, what it costs to have it done right, and the one situation where you should stop and call someone else entirely.

Why Florida Homes Get Mildew and Black Streaks So Fast

Humidity is the short answer, but it's worth understanding the mechanics, because it explains why the same house in Ohio doesn't have this problem. Coastal Northeast Florida sits at high relative humidity for most of the year, gets heavy afternoon rain from June through September, and rarely has a hard freeze that would kill off mold and algae spores. That combination means organic growth on exterior surfaces never really gets a reset.

The north-facing and shaded sides of a house are usually the worst offenders, since they hold moisture longer after rain and get less direct UV exposure to kill spores. Homes near mature trees, close to the Intracoastal, or shaded by neighboring structures tend to show staining a full season or two before an identical house in full sun. Roofs are their own case — the black streaks most people blame on dirt are actually a specific type of algae, and it behaves differently than the mildew growing on your siding or stucco.

How to Remove Mildew From House Exterior Surfaces (Soft Wash vs. Pressure Wash)

This is the part most homeowners get wrong before they ever call a pro, and it's an expensive mistake to make yourself.

Soft washing uses low water pressure (think garden-hose pressure, not a power washer) combined with a cleaning solution — typically a diluted sodium hypochlorite mix with a surfactant — that kills the mildew, algae, and mold at the root and lets it rinse away over the following day or two. It doesn't just blast away the visible stain; it treats the organism causing it, which is why the results last a full season or longer instead of a few weeks.

Pressure washing uses high-pressure water alone, with no biocide, to physically strip the stain off the surface. On the right material — sealed concrete, pavers, some hardscape — that's fine. On vinyl siding, stucco, painted wood, or roof shingles, high pressure can:

• Force water behind siding panels and into wall cavities, leading to hidden moisture damage
• Strip paint and etch stucco finishes
• Drive granules off asphalt shingles, shortening roof life and voiding some manufacturer warranties
• Leave the mildew's root structure intact, so it grows back within a month or two, often worse than before

The rule of thumb we give every customer: soft wash anything painted, stuccoed, sided, or shingled. Pressure wash only hard, sealed, non-porous surfaces like concrete driveways and pavers. If a company shows up and only owns a pressure washer, that's your sign to call someone else — a proper soft-wash setup requires different equipment, a metered chemical injection system, and someone who knows dilution ratios for your specific surface.

What Causes Black Streaks on Roofs in Florida

Those dark streaks running down a shingle roof aren't soot, dirt, or shade — they're Gloeocapsa magma, a blue-green algae that feeds on the limestone filler in asphalt shingles. It travels by airborne spores, which is why you'll often see it start on the north-facing slope and spread from there, and why neighborhoods tend to develop it roof-by-roof over a couple of years as spores move from house to house.

It's cosmetic more than structural in the early stages, but left alone it holds moisture against the shingle surface, which shortens shingle life and can void some roofing warranties if a manufacturer determines it wasn't maintained. Roof-specific soft washing uses a lower-pressure, longer-dwell chemical application than a wall or stucco wash, since shingles are more fragile and granule loss is a real risk if it's rushed. This is one job worth hiring out — even a soft wash on a roof means someone standing on it, and most homeowners shouldn't be doing that themselves regardless of the cleaning method.

Mildew on Stucco: What Makes It Different From Siding or Roofing

Stucco is porous. That's the whole story. Where vinyl siding or a painted roof shingle sheds water off the surface, stucco absorbs it, which means mildew doesn't just sit on top — it gets a foothold slightly below the surface, in the texture and hairline cracks that almost every stucco home develops over time.

That has two practical effects. First, stucco mildew tends to come back faster than siding mildew if the underlying moisture problem (a sprinkler head hitting the wall, poor drainage at the foundation, gutters dumping water down a corner) isn't fixed alongside the cleaning. Second, stucco needs a gentler chemical concentration and more rinse time, since aggressive treatment can discolor or degrade the finish coat, especially on older or hand-troweled stucco common in Ponte Vedra's older neighborhoods.

If you're dealing with mildew on stucco specifically, ask whoever you hire whether they're adjusting their mix for stucco versus siding. If they give you a flat answer without asking about your surface, that's a red flag.

Mildew Removal Cost in Jacksonville, Ponte Vedra, and St. Johns

Pricing depends on the size of the house, the surface type, and how long the staining has been allowed to build up. Here's what homeowners in our service area are typically paying in 2026:

Heavier, long-neglected staining, hard-to-reach second-story sections, or homes shaded by trees on multiple sides tend to land at the higher end of each range. Most companies price the whole-house job as a flat rate rather than hourly, so get a firm quote based on square footage rather than a time estimate.

DIY vs. Hiring a Pro — and When Indoor Mold Means Calling a Licensed Remediator

A small, isolated patch of mildew on a shaded corner of siding is a reasonable DIY job: a pump sprayer, a diluted bleach-and-water or dedicated mildew-cleaner solution, low-pressure rinse, and basic safety gear (eye protection, gloves, and care around landscaping that bleach will kill). Where DIY gets risky is scale and height — a full two-story exterior or any roof work involves ladders, chemical handling in volume, and protecting landscaping and pool equipment from runoff, which is exactly what a pro's setup is built to manage.

Here's the line that matters most, and it's not optional: this article is about exterior surfaces only. If you're seeing mold or a musty smell inside the home — in a bathroom, around a window, in an attic, or after water intrusion — that is a different problem with a different legal category. Under Florida law, indoor mold assessment and remediation over a certain size threshold requires a licensed mold assessor and a licensed mold remediator, and it is not a job a general handyman is licensed to perform. Exterior mildew and algae removal doesn't fall under that licensing requirement, but if you're unsure which side of that line your situation is on, treat it as indoor and call a licensed remediation specialist. Getting that wrong isn't just a bad paint job — it can mean a health and legal issue you didn't need to create.

How Often You Should Wash Your Home's Exterior in Florida

Most homes in Ponte Vedra, Jacksonville Beach, and St. Johns need a soft wash once every 12 to 18 months to stay ahead of visible staining. Shaded homes, homes near mature landscaping, or homes closer to the water may need it closer to annually. Roofs typically need treatment less often — every 2 to 3 years — unless streaking is already visible, in which case it's worth doing sooner rather than letting it set deeper into the shingles.

Staying on a schedule is cheaper than waiting. A house that's had a year of buildup takes a stronger treatment and more time to fully clean than one that's washed on schedule, and it protects your paint, stucco finish, and roofing investment in the process.

FAQ

Is it safe to pressure wash my house myself to remove mildew? Not on siding, stucco, painted surfaces, or roofing. High pressure can force water behind panels, strip paint, and etch stucco, and it doesn't kill the mildew at the root, so it typically grows back within weeks. Pressure washing is fine for concrete driveways and sealed pavers.

What kills mildew on the outside of a house? A diluted sodium hypochlorite (bleach-based) solution with a surfactant, applied at low pressure and given time to dwell before rinsing, is the standard professional treatment. It kills the organism at the surface and slightly below it, rather than just physically removing the visible stain.

Will mildew removal damage my landscaping? It can, if it's done carelessly. A professional soft wash includes pre-wetting and protecting nearby plants, and rinsing runoff away from root zones. If you're doing it yourself, cover sensitive plants and rinse the area well afterward.

How much does it cost to remove black streaks from a roof in Florida? Roof-specific soft washing to remove algae streaking typically runs $400 to $800 depending on roof size and how established the staining is. It's cheaper and safer than a pressure wash, and it won't void a shingle warranty the way high-pressure cleaning can.

Can mildew removal be combined with other exterior work? Yes — it's common to pair a soft wash with gutter cleaning, driveway pressure washing, or exterior caulking touch-ups on the same visit, since a crew is already on site with equipment set up.

When should I call a licensed mold remediator instead of a handyman? Any time the mold or mildew is inside the home — behind walls, in an attic, around a leak, or causing a musty indoor smell. Florida requires licensed mold assessment and remediation for indoor mold above a certain size, and that's a different job from exterior mildew cleaning.

If your siding, stucco, or roof is showing streaking or green-black staining, Ponte Vedra Handyman can take care of it the right way — soft wash, not a pressure washer that just moves the problem around. We serve Ponte Vedra, St. Johns, Jacksonville Beach, Neptune Beach, and Atlantic Beach, and we'll tell you honestly if what you're dealing with needs a specialist instead. Call (904) 780-4116 to get a straight quote, or check out our outdoor and yard services in Ponte Vedra and St. Johns pages for related work. More home maintenance guides are on our blog.