In the Pacific Northwest moss growing on your roof can affect the water tight integrity of your roof and if it gets too bad your insurance company may cancel your insurance policy or refuse to renew your homeowner's insurance until the moss is properly removed and the roof is inspected (FYI - Insurance companies will periodically check homes that they have insured).
As in any home maintenance or repair project, if you have any questions consult a professional. For your information, I have provided some roof maintenance tips below.
An ounce of prevention ... The best prevention for roof moss is copper ridge and hip caps. They are expensive but they work.
If you ask around about a roof moss problem some people will tell you that a mild laundry detergent will kill the moss. However, it would be more accurate to say that the zinc phosphate in the detergent kills the moss and there are better chemical solutions than laundry detergent. For example, a soap-based treatment called Moss Aside (see gardensalive.com) and I have also heard people recommend Lilly Miller Moss Out, or Worry-Free Moss.
If you have moss growing on your roof you should follow a 3 step procedure:
- Kill it;
- Remove it; and
- Prevent it.
Professionals advise that you proceed cautiously when applying chemicals to your roof. They recommend that you try the least toxic product available before taking more drastic measures and they suggest that you try it in the least visible part of your roof first.
Moss Aside should be applied in the spring or fall using a garden sprayer, mop, or brush.
When the moss is dead flush it off the roof with a pressure washer making sure to point the pressure washer down the roof to avoid driving water under the shingles.
After the roof is cleaned and clear of moss, you can discourage future re-growth by installing zinc strips at the peak and at down-roof intervals (see z-stop.com). After installation rainwater washing over these strips releases zinc carbonate into the storm water that washes over the roof which treats the shingle granules and prevents or significantly reduces moss growth.