How often should you pressure-wash your siding?

Why bother

Grime and algae age the siding early. A thorough-tier job. Skippable when life's busy, worth it when it isn't.

What the job involves

1. Pre-treat first, then let it sit. A mildewcide or a bleach-and-detergent mix sprayed on and left to dwell does the actual work, dissolving the algae and mildew. Brute pressure on its own just smears it around and chews up the siding.
2. Use the least pressure that works. For vinyl that's roughly 1,300 to 1,600 PSI with a wide fan tip, kept a foot or two off the wall. Most pros skip the force entirely and soft-wash with chemicals, which is the safer way to go.
3. Spray top-down at a slight downward angle so the water sheds off the laps. Never aim up, and never straight into seams, soffit vents, or under the laps. That drives water behind the siding, which is the one thing you're trying not to do.
4. Work in sections and rinse before the solution dries, wand always moving so you don't streak or blast one spot. Steer clear of windows, lights, and anything electrical, and don't do it on a hot, dry day when everything flashes off.

Do it yourself, or pay someone?

Yourself on a single-story home, if you respect the pressure limits and spray downward. A rented or owned washer plus cleaner is the main cost. Hire it out for two- and three-story homes (ladders and high reach) or heavy mold: a whole-house wash averages about $311 and usually runs $100 to $705, with two-story homes $400 to $1,400 and three-story $700 to $1,800.

What skipping it costs

$100 to $3,400 is what the hidden repair runs once growth and trapped moisture have done their work, not the wash itself. Algae and mildew hold water against the wall, and on lap-sided homes driven rain works it in behind the panels at the joints and corners. With no sound weather barrier underneath, the sheathing rots: dry-rot repair runs $100 to $2,000, and mold remediation behind the siding $1,150 to $3,400. The wash that would have prevented it runs $150 to $1,400, and a single-story one you can do yourself for the price of some cleaner.

Signs it's overdue

• Green, gray, or black streaks and a chalky, dirty film on the siding, worst on the north and shaded sides where algae and mildew like to settle.
• Spots that feel slimy, or growth you can wipe off by hand. That's mildew taken hold, not just a layer of dust.
• It's been more than a year since the last wash, or more than six to twelve months if the house is humid, coastal, or sits in heavy shade.

When to start thinking about it

Give yourself about 14 days' notice. That's when Grumpty starts grumbling, so it doesn't land on you the day it's due. Mark it done and Grumpty sets the next one, every 12 months, so you can go back to forgetting it exists.

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