Mold can be potentially very harmful to your roof. Once accompanied by fungi, lichen is produced. Lichen is not good for your roof because it has roots which feed on the limestone that is mixed in with the sand granules that are in your shingles. If the lichen problem is not addressed, it will grow and spread, along with its roots. If left untreated, these roots will eat holes through your shingles, causing major roof issues.