How Often Should You Pressure Wash Your House?
How often should you pressure wash your house? The honest answer is: when it needs it, not on a fixed calendar. A house that faces south with full sun and no tree cover can go a long time looking fine. A house with a shaded north wall next to a tree line can start showing green or black staining within a year. Same street, same builder, different exposure — different answer.
What determines how often you should pressure wash your house
A calendar date is a convenient guess. What actually drives how often a house needs washing is exposure — how much sun, shade, and moisture each wall gets.
- Sun versus shade. North-facing and heavily shaded walls stay damp longer after rain or dew. That extra moisture is exactly what algae and mildew need to establish, so shaded siding typically needs attention sooner than sun-baked siding on the same house.
- Tree cover and overhanging limbs. Trees close to the house drop pollen, sap, and leaf debris, and they block airflow and sun that would otherwise dry the siding out between rains.
- Proximity to fields, gravel, or a busy road. Homes near open farmland, gravel drives, or higher-traffic roads pick up more airborne dust and grime, which builds a film on siding and concrete faster than a house set back on a quiet, paved street.
- Gutter overflow. Clogged or undersized gutters that overflow during heavy rain leave streaking down the siding directly below them — a localized problem that shows up faster than general dirt buildup across the rest of the house.
- A humid Midwest summer. Warm, humid stretches through the growing season are close to ideal conditions for the green-black film that forms on siding, which is why homes in this region often need washing more often than the same house would in a drier climate.
Different surfaces age at different rates
"The house" is really several different surfaces, and they don't get dirty at the same pace or for the same reasons.
- Siding — vinyl, wood, stucco, or brick — collects the algae, mildew, pollen, and dust described above. This is usually the most visible sign that a wash is due.
- Concrete driveways and walkways pick up oil, tire marks, and general grime, and they also grow their own dark algae staining, especially in shaded or low-drainage spots.
- Wood decks gray and roughen as UV and moisture break down the wood surface, and they can develop the same algae film as siding if they don't get much sun.
- Fences follow a similar pattern to decks, with the added factor of ground-level splashback and grass or mulch contact along the bottom rail.
- Roofs develop a different problem entirely — see below.
Those black streaks on the roof aren't dirt
The dark streaks that show up on asphalt shingle roofs, usually starting on the north-facing slope, are a cyanobacteria called gloeocapsa magma. It isn't shingle damage by itself, and it isn't ordinary dirt — it's a living growth that spreads across the granule surface over time. Because it's biological rather than a surface stain, it needs to be treated differently than siding grime, with a wash approach suited to shingles rather than the same method used on a driveway or a wall. A roof on the same house as freshly washed siding can still be well overdue if nobody has looked at it separately.
Timing it around a Metro East calendar
In O'Fallon and the surrounding Metro East, spring and early fall are the practical windows for most exterior washing. Freezing temperatures rule out winter work — water and cleaning solution don't perform the way they need to on frozen or near-frozen surfaces, and ice on a driveway or walkway during the job is its own hazard. Late fall, once most leaves are down but before winter salt gets tracked around, is a reasonable time to handle concrete specifically, since it clears summer buildup before salt and freeze-thaw cycles start working on the surface over winter.
Wash before you paint, seal, or stain — not after
If a paint, stain, or sealing project is coming up for siding, a deck, or a fence, the wash needs to happen before that work starts, not after. Paint and sealant applied over algae, mildew, or a dirt film won't bond properly to the surface underneath, and whatever was trapped under the new coating tends to show through or cause early failure. Washing after the fact doesn't fix that — the surface needs to be clean before anything goes on top of it.
So, how often should you pressure wash your house, really?
For most homes in this area, once a year to once every two years is a reasonable range, with the shaded, tree-covered, high-moisture side of that range needing the more frequent visits and the sun-exposed, well-drained side needing less. But the range is a starting point, not the rule. The real trigger is what you can actually see on the wall, the driveway, or the roofline — streaking, a green or black tint, a dull gray film that wasn't there last year. If you're not sure whether what you're looking at is worth addressing yet, the difference between soft washing and pressure washing also matters for how it gets handled — see soft washing vs. pressure washing for how that split works by surface. Otherwise, tell us what you're seeing and where, and we'll take a look — request a quote.