If the siding on your Philadelphia home is turning green on the shaded side or gray and streaked near the downspouts, you're looking at algae, mildew, and grime that builds up over time. Our humid Pennsylvania summers and wet springs give it everything it needs to spread, especially on north-facing walls that never fully dry out.
The buildup is more than an eyesore. Algae and mildew hold moisture against the siding, which can speed up wear on paint and finishes. And once one section turns green, spores spread quickly to neighboring panels, so a small patch rarely stays small.
The wrong fix is blasting it with high pressure. On vinyl siding it can force water behind the panels, and on wood or painted surfaces it can strip the finish and leave marks you'll see for years. The right fix is a proper house siding wash: a cleaning solution applied at gentle pressure that kills the algae and mildew, followed by a careful rinse.
After a professional siding washing, the green and gray are gone and your home looks freshly painted again. Most homes stay clean for a couple of years before needing another wash, depending on how much shade and moisture your siding gets.