Preventing & Removing Roof Moss

photo by: Dave Bleasdale

There are a multitude of methods for killing moss and retarding its growth. Unfortunately there are side effects to all methods. Roofs can be slippery and dangerous work surfaces.  Additionally, many of the chemicals can burn you, as well as kill your plants and yard. Several of these chemicals are dangerous to wildlife and bad for the environment. Listed here are some of the more common and effective options for chemical control of roof moss.  A few options have been omitted due to health and safety concerns or because they are generally ineffective.

Zinc Metal Strips

Environmental effects: Low
Safety: High
Effectiveness: medium
Method of application: nailed or screwed onto roof.
Info: Zinc Metal Strips , Zinc Flashing, and flashing are generally effective at preventing moss growth, primarily due to zinc leaching out of the metal when it rains. Unfortunately it is fairly ineffective at killing moss already on the roof. Some types of moss are resistant. But what zinc metal strips and flashing lack in killing power they make up for in longevity, often zinc strips can retard moss growth for up to 10 or 20 years. The man safety hazard is falling and injury during installation. The runoff from zinc strips increase if exposed to acids (like some roof cleaning chemicals).

Potassium Fatty Acid Salts

Environmental effect: Medium
Safety: High
Effectiveness: Low
Method of application: Chemical application sprayer
Info: Potassium acid salts from fatty acids are naturally occurring, and are harmless to most plants. It is applied with a chemical sprayer. It will not stain your roof, but can have little effect on highly developed moss patches.

Zinc Sulfate

Environmental effects: High
Safety: Medium
Effectiveness: Very High
Method of application: Powder (1 pound per 100 Sqft), or Chemical application sprayer (3/5 dilution)
Info: Zinc Sulfate is highly effective, when properly applied it can inhibit moss growth for 2 to 5 years. It is not environmentally friendly, and will kill fish and invertebrates. Local environmental impact laws my ban its use.

Bleach

Environmental effects: Medium
Safety: Medium
Effectiveness: High
Method of application: Chemical application sprayer.
Info: Bleach can control moss for up to a year. Bleach will kill plants and your yard if you do not properly wash it down. If applied at too high of a concentration if can corrode metals.

Conclusion

There are many other ways to remove moss. Remember that using these methods will involve risk of physical injury and death. A dirty roof is a slippery surface, and you should follow all manufacture directions for applying or installing any of these methods. The physical removal of moss is generally best achieved by roof cleaning with a pressure washer.