Moss, Mildew And Algae: Your Home Exterior's Big Enemies

Fuzzy mounds of moss on your roof, or streaks and patches of mildew or algae on your siding, make your home's exterior look bad. They can also trap moisture, causing problems. Moss, mildew and algae need moisture and they all thrive in shade.

Cleaning Up the Mess

Moss usually grows on the shaded north side of a roof, although it can grow on any side if there is sufficient shade and moisture. You can use a pressure washer to remove it from steel or aluminum siding, but more care is required if it's growing on vinyl, brick or wood siding, or thriving on your asphalt shingles.

Mix up a solution of equal parts bleach and water. Bleach both kills the moss and algae, while removing the stains. Spray the mixture on the roof or home exterior, taking care not to get it on any plants near your home. Scrub siding with a stiff brush until it's clean, and then rinse with clear water. For the roof, pull a handled deck brush's bristles down the roof dislodge the moss, but don't push upward and lift the shingles.

Keep Your Roof Clear

Moss on a roof works its way between and under the shingles, lifting them up so water can get it in. This also weakens the shingles, so they are more likely to break or come loose. You or your roofer can make a few changes that will keep the moss and algae from growing back.

  • Zinc and copper prevent moss and algae growth. Your roofer can install a 6-inch wide strip of one of these materials underneath the topmost row of shingles. When it rains, the zinc or copper leaches down your roof and kills any moss or algae that tries to grow.

  • Ridge caps coated in zinc or copper are another option that works the same way as the moss strips beneath the shingles.

  • Trim back trees so their branches don't overhang and shade the roof. The more sun and heat on your roof, the less moss and algae.

  • Don't let fallen leaves or other debris sit on your roof or in the gutters. Moss, algae and mildew can thrive in the trapped moisture beneath the debris.

Fresh Siding and Walls

If your walls are suffering the most exterior damage, a combination of regular cleaning and moisture management can keep them looking nice.

  • Trim back plants so that air can circulate between the plants and the wall. This helps minimize mildew, mold and algae.

  • Don't let debris, whether it's a mound of soil or a mound of leaves, rest against the walls of your home. Increased moisture isn't good for your siding.

  • Repaint wood siding if the old paint is showing signs of wear. Mold and mildew growth on wood can cause your siding to rot. A fresh coat of latex exterior paint protects the wood, so even if mildew invades, it can't penetrate into the wood.

  • Crumbling mortar can invite moss problems onto your brick exterior. Have the mortar repointed, which provides fresh mortar between the bricks so moisture doesn't get between them.

A clean house begins outside. Keeping your home's exterior free of moss and algae can result in less maintenance when it comes to your roof and siding. For more professional advice, contact a company like Onit Roofing & Exteriors Inc.