Lichen on a roof is more than just an eyesore; it is a living organism that actively works to break down the surface of your shingles. This composite organism, made of fungus and algae, holds moisture against the roofing material, which can lead to granule loss, moss growth, and premature deterioration. If left unchecked, it can significantly shorten the lifespan of your roof. Understanding how to remove lichen safely and effectively is a critical part of home maintenance.
Why Lichen is a Serious Roofing Issue
Before diving into the removal process, it is essential to understand why lichen poses such a threat. Unlike dirt or pollen, lichen roots into the shingle substrate to access moisture. As it grows, it lifts the protective granules off the asphalt mat beneath. Once these granules are gone, the underlying material is exposed to the sun’s UV rays, leading to cracking and blistering. Furthermore, the trapped moisture creates the perfect environment for wood rot in the deck and provides a pathway for winter ice dams.
Assessing the Situation
Identifying Lichen vs. Moss
Many homeowners confuse lichen with moss, but the removal strategies for each are different. Moss is a non-vascular plant that grows in damp, shaded areas; it feels soft and can be brushed away relatively easily. Lichen, however, feels crusty or scaly and is firmly attached to the shingle. It usually appears in shades of gray, green, or black. If you can scrape it off easily with your fingernail, it is likely moss. If it resists scraping and looks painted on, it is lichen.
Inspecting the Damage
Before you begin cleaning, inspect the roof for soft spots or spongy areas. These indicate that the lichen has already caused significant damage to the decking beneath. If the roof feels soft or you see exposed tar, it is a sign that the structure may be compromised. In these cases, cleaning the surface will not solve the problem, and you may need to consult a professional roofer to assess the structural integrity before proceeding.
The Optimal Cleaning Window
Timing plays a crucial role in the effectiveness of your cleaning efforts. The ideal time to clean a roof is during the cooler parts of the day, such as early morning or late evening. Cleaning a hot roof with chemicals can cause the solution to evaporate too quickly, reducing its effectiveness. Additionally, you want to ensure the surface is dry enough to walk on safely but cool enough that the cleaning agents can dwell on the lichen to break it down.
Mechanical Removal: The Eco-Friendly Approach
For those who prefer non-chemical methods or have concerns about runoff into landscaping, mechanical removal is an option. This process involves physically dislodging the lichen using low-pressure methods. It is labor-intensive but effective for smaller areas or maintenance after chemical treatment.
Step-by-Step Manual Cleaning
- Start by setting up a stable ladder and wearing non-slip shoes to ensure safety.
- Use a long-handled, soft-bristle brush. Stiff plastic brushes are ideal, while metal brushes should be avoided as they can scar the shingles.
- Gently scrub the affected areas in an upward motion, following the grain of the shingles. Avoid vigorous scrubbing or "sawing" motions, as this can damage the asphalt surface.
- Rinse the area thoroughly with a low-pressure garden hose to wash away the dead lichen matter.
Chemical Treatment: The Most Effective Solution
For widespread lichen growth, a chemical solution is often the most efficient and thorough method. The most common and effective ingredient is sodium hypochlorite, commonly known as liquid bleach. When diluted correctly, it kills the lichen at its roots without harming the asphalt shingles. Oxygen bleach (sodium percarbonate) is a viable alternative for those concerned about the environmental impact of chlorine.
Preparing the Solution
Mixing the solution correctly is vital. For sodium hypochlorite, a standard mixture is one part bleach to three parts water. For oxygen bleach, the ratio is typically one cup of powder to one gallon of warm water. Stir the solution gently until fully dissolved. You will need a garden sprayer or a pump-up sprayer to apply the mixture evenly across the roof surface.
Application Process
Apply the solution to the roof, starting from the bottom and working your way up. This ensures that the runoff cleans the lower sections as it drips down. Saturate the lichen patches thoroughly so the solution runs down the sides of the house. Allow the solution to dwell on the roof for 15 to 20 minutes. Do not let it dry on the surface; you may need to mist it lightly if the weather is particularly dry. After the dwell time, rinse the roof thoroughly with a garden hose, starting again from the bottom.
Preventative Measures and Maintenance
Once the roof is clean, you can take steps to prevent regrowth. Zinc or copper strips are a highly effective preventative measure. When installed along the ridge of the roof, rainwater washes microscopic amounts of zinc or copper ions down the roof surface. These ions are toxic to lichen and moss spores, preventing them from establishing a foothold. Trimming overhanging tree branches to allow more sunlight onto the roof also helps, as UV rays naturally inhibit lichen growth.
Safety Considerations
Roof cleaning can be dangerous. If your roof is steep, high, or difficult to access safely, it is always better to hire a professional. If you choose to do it yourself, ensure you use a sturdy extension ladder, wear a harness if possible, and work with a spotter. Never walk on a wet or algae-covered roof, as the surface becomes extremely slick. Protect your skin and eyes with gloves and goggles, and cover any delicate plants near the foundation, as the runoff can kill grass and shrubs.