Moss is an organism that doesn't have roots and so is free to grow on roofs of commercial and residential buildings.  Typically moss will grow on north facing slopes which have more shade and moisture than other faces of the building. Left unchecked, moss can cause damage to your roof including composition shingles and cedar shingles and shakes. Moss and algae can be removed by pressure washing your roof, but to ensure that it does not return additional treatments are typically required. One such treatment we offer is the application of zinc strips to your roof.  This treatment is a pesticide free alternative to the common zinc-sulphate treatment which is toxic in certain high exposures. Zinc strips, measuring just three inches wide, are attached to the top of your roof, just below the peak.  As rain water runs down your roof and flows over the zinc strips, a tiny amount of the zinc dissolves into the rain water and forms a zinc carbonate which coats the roof and prevents any moss and algae from growing. The Northwest Coalition for Alternatives to Pesticides advocates the use of simple zinc strips as an effective way of controlling moss and algae growth without causing exposure to toxic and harmful chemicals. They also recommend cleaning your roof at least twice a year - in the fall and possibly the spring.  Cleaning your roof will also remove other debris that can cause your roof to retain more moisture and therefore encourage moss growth. If your roof requires moss and algae control, call one of our representatives today to schedule an appointment. Contact details: For more information, please contact a Northwest Window Maintenance representative at (206)-824-2400, or cell (206)-387-5620. Alternatively, you can email us at: info@Northwest-Windows.com