Vinyl siding is one of the easiest surfaces to clean and one of the easiest to cause expensive damage to, and the difference is a single habit.
The rule
Never spray upward under the laps.
Vinyl siding is lapped horizontal boards with an air gap behind them. Water driven upward goes behind the siding into the wall cavity and stays there, and the result is a rot and mold problem that costs orders of magnitude more than dirty siding ever would.
Angle slightly downward, or straight on. Everything else on this page is technique; this is the rule.
The cleaner does the cleaning
The black streaking on a shaded wall is mildew and the green film is algae. Both are alive and both are in the surface texture. Pressure removes the visible layer and leaves the organism, which is why a pressure-only wash looks clean for a few weeks.
A house wash, given five to ten minutes of dwell time, kills it and buys you a season or more. This is the whole argument of soft wash vs pressure wash, and it is why professionals clean siding at low pressure.
Bottom-up to apply, top-down to rinse
This confuses people, and the reason is streaking.
Applying bottom-up means cleaner is never running down over dry siding, which is what creates the clean-streak-on-dirty-wall pattern. It also lets you see your coverage as the foam builds.
Rinsing top-down means dirty water always runs over wall you have not yet rinsed, rather than over clean wall.
Reaching the upper story
With an extension wand from the ground. Not a ladder. The gun kicks, your footing is on a rung and both hands are busy — this is the most dangerous thing a homeowner does with one of these machines.
A 21-foot telescoping wand covers a standard two-story wall and reaches the soffits. A brush head on the end does the agitation that pressure should not.
Things to check before you start
Failed caulking around windows and doors. Pressure finds the gap.
Cracked or loose panels. Water goes straight behind them.
Electrical fittings, outlets and the meter. Cover or avoid entirely — see surfaces you should never pressure wash.
Dryer vents and air bricks. Do not spray into them.
Your planting. Run-off concentrates at the base of the wall, which is where the beds are. Pre-wet, keep wetting, rinse generously afterwards.
Which machine
A gentle one. This is a low-pressure job with good detergent delivery and reach, so the expensive gas machine is a liability rather than an advantage — the picks for siding.
For a single-story wall you can skip the pressure washer entirely: a pump sprayer to apply, dwell time, and a garden hose to rinse does the job.
