Soft washing or pressure washing: what siding actually needs

The green or grey film that builds up on siding, most of all on the shaded north side of a house, is usually algae and mildew rather than dirt. It grows back from whatever is left behind, which is why hosing it off only works for a while.

Why not a pressure washer

High pressure can drive water up behind the overlapping panels of vinyl siding, where it soaks the sheathing and stays. It can also strip paint, gouge softer materials and force water past the seals around windows, doors and vents.

Soft washing works the other way round. A cleaning solution is applied at low pressure, left long enough to kill the growth, and rinsed off. The solution does the cleaning, and the water pressure is not much more than a garden hose gives.

What gets protected first

Plants along the foundation are soaked with plain water before the solution goes on and rinsed again afterwards. Outlets, light fittings and vent openings are covered. The rinse runs from the top of the wall down, so nothing drips across a section that is already clean.

While you are looking at the wall

Check the gutters, the downspouts and the vent caps. An overflowing gutter streaks the siding below it, and a downspout that empties against the foundation puts water where the house least wants it.

A dryer vent cap clogged with lint shows up as grey fuzz on the wall around it. That one is worth a closer look, and Why the dryer takes two cycles to dry one load explains what it means for the dryer inside.

Those are the parts of the outside wall that exterior cleaning takes in: the siding washed, the gutters cleared and the vent caps checked while the ladder is up.