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

The short answer, siding by siding

Soft wash everything. Correct pressure at the wall for a house wash is roughly 100 to 500 PSI, about what a strong garden hose delivers, and the cleaning is done by a dilute sodium hypochlorite and surfactant mix with dwell time, not by force. The ceilings, when pressure is used at all: vinyl, up to about 1,500 PSI with a 40-degree tip aimed straight at the wall and never angled up under the laps. James Hardie fiber cement, no more than 1,500 PSI with a wide fan held six feet back, and hose-and-brush only on ColorPlus prefinished board. LP SmartSide, under roughly 1,000 PSI and never into a cut edge. Traditional three-coat stucco, under 1,000. EIFS, no pressure washer at all. Brick is mechanically the toughest surface on this list and is limited entirely by its mortar joints. Cedar and bare wood, under 500 PSI and a completely different chemistry.

Vinyl and aluminum: the angle matters more than the PSI

Vinyl is a lap system. Each course hangs over the one below with an open channel behind it, designed to shed water running down, not water driven up. The Vinyl Siding Institute's own cleaning guidance is to keep the stream pointed straight at the wall, never upward. A 15-degree tip angled under a lap at 2,500 PSI will push water behind the housewrap in seconds, and you will not see the consequence for two years. The other issue is chalking. On vinyl past roughly 20 years, and on nearly all painted aluminum siding, the surface pigment has oxidized into a chalky film. Washing takes it off, and it does not come off evenly, so a clean wall can read blotchier than the dirty one did. That is a paint problem, not a dirt problem. No wash fixes it, and we say so before we quote rather than after.

Fiber cement and LP SmartSide: the manufacturer limits and the edges that fail

James Hardie's care literature points owners at a garden hose and a soft brush first and caps pressure washing at 1,500 PSI with a wide fan tip held at least six feet from the wall. On ColorPlus prefinished board, treat the coating like paint and skip the pressure washer entirely. Check the current care sheet for your specific product, because warranty language changes. LP SmartSide is engineered wood strand under a resin overlay: the face is tough, the cut edges are not. Field cuts at windows, corners, and the bottom course are supposed to be sealed with primer at install, and on plenty of valley builds they were not. Water parked on an unsealed 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; a wash day is a good time to find out you do not have it.

Stucco, EIFS, and brick: harder-looking than they are

First, find out which stucco you own. Knock on it. Traditional three-coat over lath rings solid; EIFS, which is acrylic finish over foam board, sounds hollow and gives slightly under a knuckle. EIFS gets no pressure washer, period. Barrier-type EIFS installed before the mid-1990s has no drainage plane behind it, so water you force in stays in and rots sheathing. Soft wash, low volume, rinse from the top down. Traditional stucco handles a wide fan under 1,000 PSI, but seal any crack wider than about 1/16 inch first; hairline shrinkage cracks are normal and fine. Brick survives almost anything the brick itself sees, and then the mortar gives up. Blasting joints at 3,000 PSI erodes them, and repointing runs $8 to $15 per square foot. Skip acid on brick unless a mason says otherwise, since acid cleaners can pull manganese out of the units and leave brown stains that are worse than the dirt.

Cedar and bare wood: the one siding where the standard mix is wrong

A normal house wash mix is sodium hypochlorite. On cedar shakes, bevel siding, or T1-11 that is bare or stained rather than painted, hypochlorite bleaches lignin, lifts the grain, and can turn a warm cedar wall a dull gray-white that only sanding reverses. Wood restoration uses a different chemical: sodium percarbonate, which is oxygen bleach, at roughly 4 to 8 ounces per gallon, kept wet for 10 to 15 minutes, rinsed under 500 PSI, then neutralized with an oxalic acid brightener that also pulls tannin and rusted-fastener staining back out. Above about 800 PSI you fur the surface, and furred cedar drinks stain unevenly forever after. This is a restoration job, not a house wash, and it is only worth doing if you are re-staining within a couple of weeks. If you are not, we will tell you to wait and book it with the stain.

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

The black organic streaking that drives house washing in the Southeast is uncommon here. At roughly 11 inches of annual rain, valley siding carries farm-field silt, road dust, pollen, cottonwood fluff from the late-May drop, and hard-water calcium from sprinklers. Green algae shows up on north walls and under deep eaves, almost nowhere else. That means most of the work is surfactant and rinse, not heavy chemical. Temperature window: below 40 degrees we do not wash, below 50 dwell times roughly double, and above 90 on a sun-facing wall the mix flashes dry and streaks, so we work the shaded elevations first. Reflekt quotes house washing at $0.18 per square foot of measured wall area, soft wash. Two jobs we will talk you out of: washing chalked aluminum or 25-year-old vinyl, which comes back blotchy and needs paint instead, and buying a wash to lift sprinkler scale, which is mineral and stays. Order matters: wash siding before the glass, never after, since a house wash sheets solution across every window.