- Q.How can I kill moss growing
on cedar shake roofs? And after I've killed the moss,
what can I put on the roof to keep it from growing
responds: Scrub the surface with a mixture of
1/3 cup household detergent, 1 to 2 quarts of
household bleach, and 2 to 3 quarts of warm water.
That should kill the moss. The detergent helps wet
the surface, and the bleach kills the growth.
To prevent the moss from returning, you have to
create conditions that won't support its growth.
It's not possible to keep all dampness off the
roof, but you can enable it to dry out faster by
cutting back overhanging trees. You can also poison
the food source of the moss by applying finishes
that contain zinc, or a solution of copper
naphthenate with 3% to 4% metal content.
Unfortunately, those finishes don't last more than
two years, so they require maintenance.
Another method is to install a ridge cap made of
zinc or copper. "Bleed" water running down the roof
surface as a result of the normal corrosion from
those metals will help reduce moss growth. Tucking
strips of copper under the butt end of the shingles
every 4 to 6 feet down the roof, leaving 1 inch
exposed, may also help.
Paul Fisette is director of Building Materials
and Wood Technology at the University of
Massachusetts at Amherst and a contributing editor
to the Journal of Light Construction