Moss growth on roofs can cause damage to the roof covering. It can block gutters and build up behind chimneys and gullies. Moss acts like a sponge by absorbing rain water and thereby increasing the weight and stress on the roof. When moss freezes it expands and can move the slates or tiles causing them to crack and leak. Roofing materials like concrete tiles, slates, and cement can all become damaged by the growth of moss.

DPR completed a project on a Leeds roof recently due to the build up of moss. The moss had caused damage to the verge tiles and the ridge tiles. After an initial survey was completed the project involved cleaning off of all moss build up to the roof covering, raking out and re-pointing of the defective verge, applying a PVA bonding solution to affected areas and also the re-pointing all of the ridge back to good.