Mold, Mildew and Algae on Louisiana Homes: Why It Grows and How to Clean It

If your siding has green streaks, your roof has dark stripes or your shady walls look dingy, you’re not alone. Louisiana’s heat, humidity and rain make it easy for mold, mildew and algae to grow on the outside of a house.

Why it shows up

These growths need moisture and shade. The north-facing side of a house, walls under deep eaves, spots near trees and areas hit by sprinklers stay damp the longest, so that’s where you’ll usually see it first. Dark streaks running down a roof are often algae.

Why it’s worth cleaning

• It makes a house look older and less cared for.
• It holds moisture against siding, trim and wood, which can speed up wear and rot.
• On decks, walkways and stairs, it can make surfaces slippery.

Pressure washing vs. soft washing

High pressure works well on hard surfaces like concrete driveways and walkways. On siding, shingles, wood and painted surfaces, too much pressure can cause damage or force water behind the siding. Soft washing uses low pressure with a cleaning solution, then a rinse, so it cleans without blasting the surface.

If you do it yourself

• Never aim a pressure washer up under siding laps, at windows or into vents.
• Wet down and protect plants before and after cleaning.
• Leave roofs to a pro. Ladders and wet roofs are dangerous.

Keeping it from coming back

• Trim back branches to let in sun and air.
• Keep gutters clean so water doesn’t spill down the walls.
• Point sprinklers away from the house.
• Plan on washing again when you see it returning.

Signs it’s more than a surface stain

Sometimes streaks are only cosmetic. Other times they point to a moisture problem behind them. Call a pro to take a closer look if you notice:

• Soft or crumbling wood on trim, fascia or soffits.
• Paint that keeps peeling in the same spot.
• Musty smells inside near an exterior wall.
• Streaks that come back within weeks of cleaning.

Those can mean water is getting in from a gutter, roof edge or gap in the siding. Fixing the source first keeps you from paying to clean the same spot again and again.

If your house needs a wash, we can take a look at a free onsite estimate and tell you what each surface needs.