North-facing vinyl in Beaverton was growing mildew, not dirt

The call came from a two-story in Beaverton’s Sexton Mountain neighborhood, off Murray Boulevard. Homeowner had lived there eleven years and never washed the siding. The north wall behind the patio cover had turned a dull gray-green. She was getting paint quotes because she figured the color had faded.

Up close it was not fade. It was mildew — powdery black colonies across the lower two-thirds of the north elevation, lighter spotting on the east wall, nothing serious on south or west.

Why north-facing vinyl goes first in Beaverton

Beaverton’s housing stock is heavy on 1980s and 90s two-stories with vinyl lap siding — Sexton Mountain, Cedar Hills, Vose, and the Cooper Mountain builds all have the same pattern. North walls sit in shade from the house itself, the fence, or a covered patio. In July the rest of the house bakes dry while the north face stays cool and damp overnight.

Add overhanging maples from the parking strips and you get a biology layer, not a paint problem. Power-washing that vinyl at driveway PSI would crack aging panels and force water behind the laps. Wrong tool.

What was on the siding

• Black mildew on roughly 280 square feet of north vinyl — uniform, not streaky like roof algae
• Green algae spotting on the east gable under a birch limb
• Spider web debris in the corners near the downspout — cosmetic, but it holds moisture
• No chalking — the vinyl pigment was intact underneath; the growth was surface-level

This was a house wash job using soft-wash technique, not a high-pressure blast. Our house washing vs pressure washing guide breaks down the PSI difference: under 500 PSI with solution on siding, 2,500-plus only on concrete.

What we did

We wet the landscaping, applied a mildew-focused soft-wash solution with a low-pressure downstream injector, let it dwell eight minutes on vinyl, and rinsed top-down with a wide fan. Hand-scrubbed the web corners and behind the downspout bracket where the growth was thickest.

While we were on site we hit the driveway and front walk with a surface cleaner — that is where high PSI belongs. Siding and concrete on the same property, two different methods.

Total time: about three hours for siding plus flatwork. The north wall transformation was obvious from the street — gray-green to original cream in one pass.

How long it lasts

On a north face in Beaverton, a proper soft wash typically buys you two to three years before mildew returns — longer if you trim back the birch and keep gutters from overflowing onto the lower courses. South walls on the same house might not need attention for five years.

We told her to skip the paint quotes. Revisit in 2028 unless the gutters start dumping debris down that wall again.

What we sent the homeowner

North elevation before and after, east gable close-up, and a driveway shot since we did the flatwork same visit. She forwarded the photos to the painter to cancel the estimate.

If your Beaverton siding looks chalky or gray on the shady side but fine everywhere else, it probably is not the paint — it is growth. 503-995-1947 for a written walk-through. We quote one number on site before we start.