Green Algae on House Siding

Signs You Have Algae on Your House Siding

Algae growth follows predictable patterns that are easy to identify:

• Green or green-black film on siding, especially on north-facing walls
• Growth concentrated in shaded areas — under eaves, near trees, on walls that receive little direct sun
• Siding feels slimy or slippery when touched
• Growth that expands noticeably from spring through fall
• Streaking pattern where rainwater runs down the siding
• Musty smell near affected walls, especially after rain

In the Madison area, algae season runs from April through October. Homes in wooded neighborhoods like Nakoma, Shorewood Hills, and areas near the Arboretum are especially prone due to tree canopy and higher ambient humidity.

Why Algae Grows on Wisconsin Homes

Climate and Humidity

Dane County averages 60-80% relative humidity during summer months. Combined with warm temperatures, this creates a perfect environment for algae colonization. Our proximity to Lakes Mendota and Monona adds additional ambient moisture.

Shade and Orientation

North-facing walls receive minimal direct UV light, which would otherwise inhibit algae growth. Mature trees that are common in established Madison neighborhoods create additional shade zones.

Organic Surface Deposits

Pollen (heavy in Wisconsin springs), dust, and airborne organic matter accumulate on siding and serve as nutrients for algae colonies. The more organic material present, the faster algae establishes itself.

DIY vs. Professional Algae Removal

What You Can Do Yourself

For small areas (under 20 square feet), a solution of one part white vinegar to four parts water, applied with a soft brush, can remove surface algae. However, this does not kill the root system embedded in siding pores, so regrowth occurs within 2-4 weeks.

Why Pressure Washing Is Dangerous for Siding

Consumer pressure washers produce 2,000-3,000 PSI — far too much for vinyl, wood, or fiber cement siding. At these pressures, water is forced behind siding panels, beneath the weather-resistant barrier, and into wall cavities. This hidden moisture causes mold, rot, and insulation damage that is invisible from outside but can cost thousands to remediate.

The Professional Soft Wash Advantage

Professional soft washing uses cleaning chemistry rather than damaging pressure to eliminate algae. The solution penetrates the algae's root structure, killing it completely rather than just removing the visible surface layer. This means 6-12 months of protection versus 2-4 weeks with DIY scrubbing.

How The Total Wash Co. Can Help

Our soft wash house cleaning service is specifically designed for Wisconsin homes and siding types:

• Low-pressure soft wash system — safe for vinyl, wood, fiber cement, stucco, and brick
• Biodegradable cleaning solutions that kill algae at the root without harming your landscaping
• Plant protection protocol — we pre-wet and cover sensitive plants before treatment
• Residual inhibitor that slows algae regrowth for 6-12 months
• Full-house treatment — we do not just spot-treat, ensuring a uniform clean appearance
• Serving Madison, Middleton, Fitchburg, Sun Prairie, Verona, Waunakee and surrounding Dane County communities

Most homes are completed in 2-4 hours. Call (608) 360-5818 for a free estimate — we will assess the severity and give you an honest price before starting.

How long does it take for algae to come back after professional cleaning?

With our soft wash treatment and residual inhibitor, most homes stay algae-free for 6-12 months. Heavily shaded areas may see regrowth sooner. Annual soft washing is the most cost-effective maintenance schedule for Wisconsin homes with recurring algae issues.

Is the green stuff on my siding mold or algae?

Most green growth on siding is algae, not mold. True mold is typically black or dark gray and grows in persistently damp areas. However, algae creates conditions favorable for mold growth by trapping moisture against your siding. Removing algae promptly helps prevent mold from establishing. Our treatment addresses both organisms.

Will house washing damage my landscaping?

Not with our process. We use biodegradable cleaning solutions and pre-wet all landscaping before treatment. We also rinse plants thoroughly after completing the wash. Our solutions break down into harmless components within hours. In years of service across the Madison area, we have never damaged a customer's landscaping.