House Washing by Siding Type: Vinyl, Hardie, Stucco, Brick, Cedar, and LP

The limits in one place, siding by siding

Soft wash all of it. At the wall, a house wash should land between 100 and 500 PSI, roughly garden-hose force, because the cleaning is done by a dilute sodium hypochlorite and surfactant mix given five to ten minutes of dwell, not by force. Where pressure gets used at all, the ceilings are: vinyl about 1,500 PSI with a 40-degree tip aimed straight in; James Hardie fiber cement 1,500 PSI, wide fan, held six feet back, and hose-and-brush only on ColorPlus prefinished board; LP SmartSide under roughly 1,000 and never into a cut edge; traditional three-coat stucco under 1,000; EIFS none at all; cedar and bare wood under 500 with completely different chemistry. Brick is the toughest material on the list and is limited only by its mortar joints. Every one of those numbers is a ceiling, not a target.

Vinyl and aluminum: the angle matters more than the number

Vinyl is a lap system. Every course hangs over the one below with an open channel behind it, built to shed water running down, not water driven up. Vinyl Siding Institute guidance is to keep the stream pointed straight at the wall. A 15-degree tip angled up under a lap at 2,500 PSI puts water behind the housewrap in about a second, and the consequence shows up two years later as soft sheathing. Heat is the limit nobody mentions: vinyl begins to soften near 160°F, so hot-water rigs stay under roughly 140°F at the tip. Then there is chalking. Swipe a dark rag across a sun-facing wall, and if it comes back gray, the pigment has oxidized. Washing removes chalk unevenly, so a clean wall can read blotchier than the dirty one did. That is a paint problem. No wash fixes it, and we say so before quoting rather than after.

Fiber cement and LP SmartSide: tough faces, vulnerable edges

James Hardie's care literature sends owners to a garden hose and soft brush first, and caps pressure washing at 1,500 PSI with a wide fan tip held at least six feet off the wall. On ColorPlus prefinished board, treat the coating like paint and skip the pressure washer entirely. Care sheets get revised, so pull the current one for your specific product before anyone starts. LP SmartSide is engineered wood strand under a resin overlay, and the face is genuinely tough while the cut edges are not. Field cuts at windows, corners, and the bottom course are supposed to be primed at install, and on plenty of valley builds they were not. Water parked on a raw edge swells the strand and the bottom lip mushrooms. So the wand stays off edges and rinsing runs downward. Both products want six inches of clearance to grade. Wash day is how many homeowners learn they have four.

Stucco, EIFS, and brick: knock before anyone sprays

Find out which stucco you own first. Knock on it. Traditional three-coat over lath rings solid, while EIFS, an acrylic finish over foam board, sounds hollow and gives slightly under a knuckle. EIFS gets no pressure washer, ever. Barrier EIFS installed before the mid-1990s has no drainage plane behind it, so water you force in stays in and rots sheathing from the inside out. Soft wash it, low volume, top down. Traditional stucco takes a wide fan under 1,000 PSI, but patch any crack wider than about 1/16 inch first; hairline shrinkage cracking is normal and fine. Brick outlasts nearly anything, and then the mortar quits. Blasting joints at 3,000 PSI erodes them, and repointing runs $8 to $15 per square foot. Skip acid unless a mason signs off, since acid cleaners can pull manganese out of the units and leave brown staining worse than the dirt.

Cedar and bare wood: chlorine is the wrong chemical here

A standard house wash mix is sodium hypochlorite. On cedar shakes, bevel siding, or T1-11 that is bare or stained rather than painted, hypochlorite attacks lignin, raises the grain, and can leave a warm cedar wall a dull gray-white that only sanding reverses. Wood takes a different chemical: sodium percarbonate, which is oxygen bleach, at roughly 4 to 8 ounces per gallon, kept wet 10 to 15 minutes, rinsed under 500 PSI, then neutralized with an oxalic acid brightener that also pulls tannin bleed and rusted-fastener streaking back out. Past about 800 PSI you fur the surface, and furred cedar takes stain unevenly from then on. This is restoration work, not a house wash, and it only earns its cost if stain or sealer goes on within about two weeks. Bare cedar starts graying again inside a month, so we will tell you to book both together.

What is actually on Treasure Valley walls, and when not to buy this

The black organic streaking that drives house washing in the Southeast barely exists here. On roughly 11 inches of annual rain, valley siding carries farm-field silt, road dust, pollen, late-May cottonwood fluff, and hard-water scale from sprinkler overspray. Green algae shows on north walls and under deep eaves and almost nowhere else, so most of the work is surfactant and rinse rather than heavy chemical. Below 40°F we do not wash. Below 50°F dwell times roughly double. Above 90°F on a sun-facing wall the mix flashes dry and streaks, so shaded elevations go first. Reflekt quotes house washing at $0.18 per square foot of measured wall, and a typical two-story valley home carries 1,600 to 2,000 square feet of wall, so $290 to $360. Two jobs we talk people out of: washing chalked aluminum, and buying a wash to lift sprinkler scale. Wash siding before glass, never after.