Mildew, Sun and Heat: Keeping Siding Looking Right

Alabama's damp climate

Warm, moist air flows north off the Gulf of Mexico through the warmer half of the year, and statewide precipitation averages 55.4 inches a year, spread fairly evenly across the months except for a drier stretch from August to October, according to NOAA's Alabama climate summary.¹ Wet walls that stay shaded are exactly where growth starts, so the north side and anything behind shrubs needs the most attention.

Green or black mildew

Iowa State University Extension explains that mold and mildew grow where it's damp and shaded with little air movement, often on the north side of a house or behind plants that sit close to the wall.² Most outdoor mold on siding isn't a health issue, but it looks bad, and the Extension says regular cleaning and removing mold early can extend the life of siding.²

Cleaning it safely

• Wash the siding about once a year with a soft brush on a hose; that's often enough.²
• For stubborn growth, the Extension suggests a mild cleaner solution, with household bleach added only if the cleaner has no ammonia. Cover nearby plants and rinse well.²
• If you pressure wash vinyl, HomeGuide advises starting on low pressure so panels don't crack.³
• Trim shrubs back from the walls to let air through.²

Fading

Fading in direct sun is one of the drawbacks HomeGuide lists for vinyl, and it notes that thicker premium panels are less prone to it.³ Vinyl can be painted for about $1 to $3 per square foot, but that may void the maker's warranty.³

Warped or "melted" panels near windows

The Polymeric Exterior Products Association says distortion like this comes from sunlight concentrated by energy-efficient low-e windows, sometimes on a neighbor's house, not from a defect in the siding.⁴ It's uncommon and needs a particular angle. The fixes it suggests are blocking that path of light, for example with landscaping, sunshades above the window or window screening.⁴

How long it lasts

HomeGuide puts vinyl at 30 to 40 years on average and more than 60 with regular cleaning, depending on climate and sun exposure; cracks, holes, warping or heavy fading are the usual signs it's time to replace.³ Fiber cement is listed at 50 to 100 years when it's installed and maintained properly.⁵