That green-black film creeping up the shady side of your house isn't dirt. It's algae — and it's alive.

It feeds on the limestone filler in your siding and the moisture that sits on the north and east walls. Rinsing it off with a hose or a pressure washer knocks the color down for a few weeks, then it comes back darker, because the root structure was never touched.

The part most homeowners get wrong

A pressure washer at 2,500+ PSI aimed at vinyl siding does three things: it drives water up behind the panels, it strips the UV layer so the siding chalks and fades, and it blows out the caulk around windows. On stucco it opens hairline cracks. On painted wood it takes the paint. Once water is behind the siding, you're looking at sheathing and insulation problems that cost thousands, not hundreds.

Siding is a soft wash job — low pressure, roughly garden-hose force, with a detergent that kills the organism and lets it rinse away. Pressure belongs on horizontal concrete, not on your walls.

What actually needs pressure

• Concrete driveways, walkways, patios — yes, with a surface cleaner, not a wand. A wand leaves zebra stripes you'll stare at for years.

• Siding, soffits, stucco, brick, painted wood — no. Soft wash.

• Roofs — never pressure. Ever. You're rinsing granules off your shingles and shortening the roof's life.

The one thing people skip that actually costs them money

Gutters. A clogged gutter overflows behind the fascia board, and rotted fascia plus a soaked soffit is a four-figure carpentry bill. A clean-out is a fraction of that. If you do nothing else this season, get the downspouts flushed and confirm water is exiting at the bottom, not the seam.

Timing

Spring and early fall are ideal — the algae is active and the temperatures let detergent dwell properly. Washing in freezing weather is mostly theater.

If you want it handled instead of handling it yourself, our packages are on this page. Ask me anything about your specific siding type or staining below — happy to tell you whether it's a DIY afternoon or a real job.