Walk around almost any house in the DMV in spring and the north side looks different: green film on the siding, black streaks under the eaves, maybe green on the fence and deck too. It's algae and mildew, and our humid summers and mild winters give it everything it needs.
WHY THE NORTH SIDE
- Less sun means surfaces stay damp longer after rain and dew.
- Shade from trees adds more moisture and organic debris.
- Sprinklers hitting the siding keep it wet.
- Nearby woods or creeks add spores and humidity.
IS IT HARMFUL?
It doesn't damage vinyl siding structurally, but it looks neglected, can stain over time, and makes surfaces slippery on walkways and decks. On painted wood it can trap moisture and shorten paint life.
HOW TO CLEAN IT SAFELY
- Soft wash, not blast. Use a siding cleaner or diluted sodium hypochlorite solution applied at low pressure.
- Let it dwell 5 to 10 minutes. The cleaner does the work, not the pressure.
- Rinse gently from the top down.
- Protect plants by pre-wetting and rinsing them.
High-pressure washing can force water behind vinyl siding, into vents and windows, and etch soft surfaces. See soft wash vs. power wash.
SLOWING IT DOWN
- Trim back trees and shrubs to let in light and air.
- Redirect sprinklers away from the house.
- Clean gutters so they don't overflow onto the siding.
- Wash once a year in spring to keep growth from building.
COST
A soft wash of a typical DMV single-family home runs $300 to $650, townhouses $200 to $400. Adding the deck, fence or walkways is usually priced per area.
Spring is the best time to wash in the DMV: growth from the damp winter is visible, and it clears the house before pollen and summer humidity.
RELATED READING
SOFT WASH VS. POWER WASH FOR VINYL SIDING
Why pressure isn't the answer on siding, what actually kills algae, and what each costs.
PRESSURE WASHING COST GUIDE FOR THE DMV (2026)
What you'll pay to pressure wash driveways, decks, siding, and patios — plus soft wash vs. pressure wash and what's actually worth doing.
HOW OFTEN SHOULD YOU WASH YOUR HOUSE?
Siding, decks, driveways and walkways: how often each needs it and the best months.
Planning a project? See our Pressure Washing service page for scope, process and recent work.
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