Mold, algae, and stains on house siding aren't just ugly -- they eat into the material over time and can cause rot behind the surface if ignored. The good news: removing mold and stains from house siding is usually a straightforward job. Here's what it costs, which methods work, and when to call a professional.

The Quick Answer

Professional house siding cleaning runs $200-$600 for most homes. Two-story homes with heavy mold run $400-$700. The cost depends on home size, siding type, and how bad the growth is.

Soft wash (1,500-2,500 sq ft home): $250-$500
Two-story home: $400-$700
Per square foot rate: $0.20-$0.50/sq ft
Mold removal from siding (isolated sections): $500-$700 average
DIY cost (chemicals + equipment rental): $50-$150

Most exterior siding cleaning uses soft washing -- a low-pressure chemical rinse -- not a high-pressure spray. The chemicals do the heavy lifting so you don't risk damaging the siding.

Mold vs Algae vs Mildew: What's on Your Siding

These three get mixed up a lot, but they respond to slightly different treatments. Knowing which one you're dealing with saves time and chemicals.

Algae: Green or black streaks, usually on north-facing or shaded walls. Most common on vinyl and fiber cement siding. Pressure washing or soft wash both work well.
Mildew: White or gray powdery spots. Shows up in humid climates. A diluted bleach solution kills it effectively.
Mold: Fuzzy black, green, or white patches. More stubborn and can penetrate porous materials. Needs chemical treatment and sometimes professional remediation if it's spread behind the surface.

For a deeper look at telling these apart and choosing the right removal technique, see our guide on algae vs mold removal for pressure washers.

DIY Methods That Work

For light mold and stains, you can tackle siding yourself before calling a pro. Here are three approaches that actually work:

Option 1: Bleach solution

Mix one part bleach to 10 parts water in a pump sprayer. Apply to the affected area, let it dwell 10-15 minutes, scrub with a soft-bristle brush, and rinse with a garden hose. This handles most algae and mildew on vinyl.

Important: Never mix bleach with ammonia-based cleaners. Pre-wet nearby plants and rinse them after treatment to prevent chemical burn.

Option 2: White vinegar

Mix 30% white vinegar with 70% water in a spray bottle. Spray on the stain, let it sit 15 minutes, scrub, and rinse. Less effective on heavy mold than bleach but safe for painted surfaces and plants.

Option 3: Oxygen bleach (OxiClean)

Mix per manufacturer instructions and apply with a garden sprayer. Oxygen bleach is color-safe, biodegradable, and works well on wood, fiber cement, and painted siding where sodium hypochlorite might cause bleaching.

Professional Soft Wash: How It Works

Professional house washing uses soft wash equipment -- low pressure (under 500 PSI) combined with a sodium hypochlorite and surfactant solution. The chemical kills mold and algae at the root, not just at the surface. Results last 12-24 months compared to 6-12 months from pressure washing alone.

The process takes 2-4 hours for a typical single-story home:

Pre-wet plants and cover exterior outlets and lights
Apply cleaning solution from bottom to top (prevents streaking)
Let dwell 5-10 minutes while the chemicals break down growth
Rinse from top to bottom with low-pressure water
Spot-treat any stubborn areas with a second application

Soft wash costs more per square foot than a basic pressure wash -- $0.20-$0.50 vs $0.15-$0.25 -- but the results last longer and there's zero risk of forcing water behind panels or damaging the surface.

When to Call a Professional

DIY works fine for light surface mold and algae on vinyl or fiber cement. Call a professional when:

Mold covers more than 10 square feet or is spreading rapidly
Stains reappear within a few weeks after cleaning (sign of moisture behind the wall)
You're dealing with wood siding that shows soft spots, swelling, or discoloration -- these are signs of rot
The home is two stories or higher and requires ladder work
The siding is older stucco, EIFS, or painted wood that's sensitive to pressure

If mold has penetrated behind the siding into the sheathing or insulation, that's no longer a cleaning job -- it's a remediation job. That's where costs jump significantly ($1,500-$5,000+ depending on scope).

Siding Type Matters

Not every siding material handles the same cleaning method. Here's a quick breakdown:

Vinyl: 1,300-1,600 PSI max, 25-40 degree nozzle, spray downward only. Soft wash preferred.
Wood siding: 500-1,200 PSI max, spray with the grain, no bleach on unpainted wood.
Fiber cement (Hardie board): 1,500-2,000 PSI, avoid direct impact on painted edges.
Brick and stucco: 600-800 PSI max, no high-pressure in mortar joints or textured stucco.
Aluminum siding: Low pressure only (under 1,200 PSI), gentle detergent, never use a zero-degree tip.

For more on cleaning different siding types, see our guide on house exterior cleaning methods.

Bottom Line

Light mold and stains on siding are a regular maintenance problem -- not an emergency. A bleach solution or oxygen bleach handles most DIY jobs. For anything heavier, a professional soft wash at $200-$600 is worth every dollar to avoid the damage that DIY pressure washing can cause. Clean siding every 1-2 years to keep mold from taking hold in the first place.

If you want homeowners to get an instant price for siding cleaning before they call you, try QuoteSnap for free. It's a calculator you embed on your website so customers can get a real number in 30 seconds -- and come to you ready to book.

Removing Mold and Stains from House Siding: Cost, Methods and Professional Cleaning 2026