Moss acts like a sponge. It retains water every time it rains or even when there's heavy dew or fog. This moisture doesn’t evaporate quickly, especially when moss spreads under the edges of shingles or tiles. When moss infiltrates these spaces, it lifts the shingles slightly, creating openings that allow water to seep underneath. This compromises the waterproof barrier of your roof and leads to wood rot, mold growth, and potential leaks into your attic or living space.

In colder months, any retained moisture in the moss or under the shingles is vulnerable to freezing. Water expands when it turns to ice, which can cause shingles to crack, warp, or separate from the roofing deck. The more freeze-thaw cycles your roof endures with moss present, the faster the deterioration process happens. Even minor cracks can turn into larger structural issues over time.

When moisture seeps below the roof’s surface, it doesn't just affect the shingles—it begins to compromise the roof decking and structural supports underneath. Prolonged dampness leads to wood rot, which weakens the roof’s ability to bear weight, especially during heavy rains or snowfall. Over time, this kind of damage may require partial or full roof replacement, often far earlier than the roof's intended lifespan.

A moss-covered roof can attract insects, birds, and rodents that see it as a safe habitat. Moss provides nesting material and a hiding place for pests. Once established, they can find ways into your attic or under eaves, causing further damage and posing potential health risks.

While less immediately threatening than structural issues, moss-covered roofs make a home appear poorly maintained. This can decrease curb appeal and property value, which is especially important if you plan to sell your home. Prospective buyers and inspectors often flag moss as a concern that could indicate underlying damage or neglect.