How to get rid of the moss on your roof
Contractor Rob Robillard answers reader questions about what damage plants and debris can do to shingles.
Q. I have a section of roof that faces north and has a lot of moss on it. Should I be concerned about this, and, if so, what can I do about it? Thank you.
LOU
A. I love moss in the woods, but not on a roof. Your situation is common; moss tends to grow on north-facing roofs, which receive less direct sunlight and stay damp longer than south-facing ones.
As a nonvascular plant, moss obtains water through its leaves, not a root system, and needs a moist environment to survive. Overhanging tree branches provide additional shade and drop debris on the roof that further holds in moisture and acts as a food source for the moss. Moss beats up your shingles, reducing their performance. It can cause the leading edges of the shingles to lift or curl, which increases the risk of blowoff in a windstorm.
There are a bunch of products you can buy to spray and forget. The most effective method I’ve seen for cleaning algae and moss from a roof, however, is a 50-50 mix of laundry-strength liquid chlorine bleach and water. This applies to all roof types. Try this:
1. Protect landscaping below the roof from runoff and wear personal protective equipment when working with chlorine bleach.
2. Apply the solution with a sprayer and allow it to soak in for 15 to 20 minutes.
3. Rinse thoroughly with low-pressure water.
4. You may need to reapply and leave it on longer, but avoid letting the solution dry completely.
5. Never use a pressure washer to clean an asphalt-shingle roof; this will cause granule loss and very likely premature failure of the roof system.
The moss will loosen over time and may be removed with a leaf blower.
If you want to be proactive, there are things you can do to discourage moss growth, such as:
■ Trimming tree branches back to allow more sunlight to reach the roof.
■ Reducing debris accumulation on your roof. I see this a lot on low-pitch roofs; leaves and branches tend not to blow off these. Use a leaf blower to clean the roof, directing the airflow down the slope to avoid driving debris under the shingle edges.
■ Keeping your gutters clean for good drainage.
■ Ensuring that gutters from an upper roof do not drain on a lower roof by extending the higher downspout into the lower gutter.
■ Adding zinc or copper strips to prevent both algae and moss buildup or applying asphalt shingles that incorporate algae-resistant copper granules.
Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to [email protected] or tweet them to @robertrobillard.
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