Moss creeps along areas of your lawn and garden and is difficult to control. The moss prefers areas with a lack of sunlight and can live on nearly any type of surface, including a roof with concrete tiles. Remove or kill the moss once, and it will simply keep coming back. The most effective way to kill moss on concrete is by removing both the moss and the conditions it needs to grow.
Brush the moss from your roof, using a scrub brush with a pole or long handle. Push the brush down the roof, knocking the moss into your yard. Avoid standing at the bottom of the roof and pushing up, as you can loosen the tiles.
Mix oxygen bleach with water, following the directions on the container; typically 1/2 cup oxygen bleach with 1 gallon water. Oxygen bleach is a powdered cleaner that won't harm the concrete tiles on your roof and doesn't have the harsh scent of full-strength liquid bleach.
Pour the mixture directly onto the moss-affected areas of the concrete tile roof. Use a scrub brush to gently work the mixture around the moss. Let the mixture sit for at least an hour. Rinse the mixture away with a garden hose or power washer.
Wash away any stains from the roof and concrete tiles with an additional application of oxygen bleach and water. Aim a power washer directly at any green or dark areas left behind by the moss. Rinse with fresh water.
Remove any trees, plants or shrubs that cover your roof. On larger trees and those with low-lying branches, trim the branches back until the pieces aren't hanging over the concrete. When you remove the plants that cover your roof tiles, you reduce the chances of the moss coming back.
Don't use liquid bleach or washing powder on the roof. Bleach that falls onto the ground kills grass and other vegetation. Bleach can discolour the roof tiles and also weaken the structure of your roof.