House washing should be done at 500 to 1,200 PSI using a soft wash approach, not at the 3,000 to 4,000 PSI used for concrete. The lower pressure protects siding, painted wood, and mortar joints while the cleaning chemistry does the actual work of removing biological growth. Using high pressure on a house exterior causes damage that ranges from stripped paint to water intrusion behind vinyl panels.
Why lower PSI is correct for siding
Siding materials, whether vinyl, fiber cement, painted wood, or stucco, are not designed to absorb 3,000 PSI water jets. At that pressure, vinyl siding seams separate and water forces into the wall cavity. Painted wood loses paint and the raw wood underneath becomes vulnerable to moisture and UV damage. Stucco, especially older applications, can crack or delaminate under high-pressure impact. Even brick, which is more durable, risks having its mortar joints eroded by aggressive pressure.
The key insight is that house dirt, algae, and mildew do not require force to remove. They require chemistry. Sodium hypochlorite breaks down and kills biological growth at concentrations that allow low-pressure rinsing to clear the surface cleanly.
PSI by surface type
Here is a practical guide to appropriate pressure ranges:
- Vinyl siding: 500 to 800 PSI maximum. Use a wide-angle nozzle and keep the wand moving.
- Fiber cement (HardiePlank): 500 to 1,200 PSI. Durable but still subject to water intrusion if pressure forces behind seams.
- Painted wood siding: 500 to 800 PSI. Lower is safer. Chemistry does the work.
- Brick (good condition): Up to 1,200 PSI. Lower if mortar is soft or deteriorating.
- Stucco: 500 to 800 PSI. Cracked stucco should not be washed at any meaningful pressure without repair first.
- Roofing shingles: 100 to 300 PSI with a dedicated soft wash system. Never use a standard wand on shingles.
What happens when pressure is too high
The damage from excessive pressure on siding is not always immediately obvious. A seam that has been forced open may not show visible water intrusion for weeks. Paint that has been partially stripped peels further over the next rain cycle. Vinyl that has been driven off its mounting channel behind the seam creates a gap that lets in moisture, insects, and debris. These are not hypothetical risks. They are the documented consequences of companies using concrete-cleaning PSI settings on residential siding.
The nozzle makes a difference too
PSI alone does not determine cleaning force. The nozzle angle concentrates or spreads the water stream. A zero-degree nozzle at 1,000 PSI concentrates far more force than a 40-degree nozzle at the same pressure. Professional house washing uses wide-angle nozzles and keeps the wand at a distance that distributes pressure safely. This is why the same machine can clean concrete aggressively and clean siding gently.
What CARE uses on Fort Worth homes
CARE runs house washing at 500 to 1,200 PSI, adjusted for the specific siding material and condition. We use a soft wash approach, applying cleaning chemistry first and rinsing at low pressure after dwell time. Our roof cleaning system operates at 100 to 300 PSI using a dedicated soft wash unit. No standard pressure wand is ever pointed at a roof. Call (945) 275-8031 or visit our house washing page to schedule a quote.