A green, moss-covered roof may look charming, but moss can create real problems when it is allowed to grow unchecked. Moss retains moisture against the roofing material and can work underneath the edges of shingles, eventually lifting them or contributing to leaks.
Before treating a roof, however, make sure the growth is actually moss. Dark streaks or stains may be algae, while thicker green growth with a soft or matted appearance is more likely to be moss. The correct treatment can depend on the type of roofing material and the type of organic growth present.
Do Not Climb Onto the Roof
The safest way for a homeowner to inspect for moss is from the ground, using binoculars or a camera with a zoom lens. Look for green growth, lifted or displaced shingles, damaged flashing, clogged gutters, and areas where tree branches overhang the roof.
We strongly recommend that homeowners do not climb onto the roof to remove moss themselves. Moss, water, and cleaning solutions can make the surface extremely slippery. A ladder, rope, gloves, and nonslip shoes do not eliminate the risk of a serious fall. Older shingles may also be brittle, and walking on them can cause damage even when no immediate problem is visible.
If moss is present on a steep roof, a tall roof, an older roof, or a roof with damaged shingles, contact a qualified roofing professional.
Never Use Bleach on a Roof
Do not use household bleach to remove moss from a roof.
Bleach and bleach-based mixtures can damage or kill vegetation below the roof. Runoff may also discolor siding, decks, walkways, and other exterior surfaces. Even when plants are covered, runoff can still reach the soil, lawn, foundation plantings, or storm drains.
Do not substitute vinegar, dish soap, laundry products, or other household chemicals without knowing whether they are compatible with the roofing material and surrounding property. Never mix cleaning products together.
Use a Product Made Specifically for Roof Moss
There are commercial products specifically formulated to treat moss and algae on roofs. If treatment is appropriate, choose a product whose label specifically permits use on the type of roof involved, whether asphalt shingles, tile, metal, or another material.
Follow the product’s instructions carefully. Some treatments are intended to remain on the roof and work gradually, while others may call for limited rinsing. Do not assume that a product is safe for nearby vegetation simply because it is marketed as natural or environmentally friendly.
Before applying any roof-cleaning product, determine where the runoff will go. Keep the solution away from:
- Plants, shrubs, grass, and garden beds
- Ponds, pools, rain barrels, and drainage areas
- Siding, decks, patios, and walkways
- Gutters and downspouts that discharge near landscaping
If runoff cannot be controlled, the treatment should not be applied. Covering plants with plastic alone is not a complete solution. The product label should provide any required precautions for vegetation, surfaces, protective equipment, application, and cleanup.
Because treating a roof involves both fall and chemical exposure risks, professional application is usually the safer option.
Avoid Pressure Washing and Aggressive Scrubbing
Pressure washing is generally not appropriate for asphalt shingle roofs. The force of the water can remove protective granules, lift shingles, damage flashing, and shorten the life of the roofing system.
Aggressive scraping or scrubbing can cause similar problems. Shingles are not designed to be pounded, scoured, or scrubbed forcefully. If physical removal is necessary, a roofing professional may use low-pressure methods and soft-bristled tools appropriate for the roofing material.
Water should never be sprayed upward beneath the edges of shingles. That can force water into areas designed only to shed water from above.
What Helps Prevent Moss From Returning?
Moss grows most easily in areas that stay damp and shaded. Several maintenance steps can reduce the likelihood of recurring growth:
- Trim tree branches that shade the roof or hang directly over it.
- Keep gutters and downspouts clear so water can drain properly.
- Remove leaves and organic debris before they accumulate.
- Correct drainage problems that keep portions of the roof wet.
- Have the roof inspected periodically, especially if moss has previously lifted shingles.
- When replacing the roof, ask about shingles designed with algae-resistant features.
Some homeowners also consider installing copper or zinc strips near the roof ridge. These are not a universal do-it-yourself solution. Installing them on an existing roof may require disturbing shingles, sealant bonds, or fasteners. A roofing professional should determine whether that approach is appropriate for the roof.
Moss May Indicate More Than a Cleaning Problem
Removing visible moss does not necessarily correct the underlying roof condition. Moss may have already lifted shingles, damaged the seal between courses, affected flashing, or contributed to moisture beneath the roofing material.
After moss is removed, the roof should be checked for:
- Lifted, cracked, or missing shingles
- Damaged flashing
- Soft or deteriorated decking
- Leaks or water stains in the attic
- Clogged gutters and downspouts
- Areas where moisture remains trapped
Moss Is Less Common in Dallas, but Roof Algae Is Not
Moss is less common in Dallas than in wetter regions such as the Pacific Northwest. However, roofs in this area can develop a dark organic growth that looks almost like black soot or powdery staining. This is often algae, sometimes referred to as blue-green algae, rather than moss. Like moss, it grows more readily in shaded or damp areas and should not simply be ignored. Roof algae is generally treated with the same basic precautions: avoid climbing onto the roof, never use household bleach, avoid pressure washing, and use only a product specifically labeled for the roofing material.
A roof that is near the end of its service life may not be a good candidate for repeated chemical treatments. In that situation, cleaning may only delay the need to address the larger roofing problem.
If you have moss on your roof or are unsure whether the growth is moss, algae, or something else, Bert Roofing can inspect the roof and explain the practical options. We provide professional roof maintenance, repairs, and replacements throughout Dallas and the surrounding area. Visit our roof maintenance service page or contact Bert Roofing to schedule an inspection.
