Why is it important to keep moss off of your roof? Moss grows tendrils that reach up underneath shingles and other roofing materials which exposes them to excess moisture such as driving rain. With the shingles uplifted it is harder for the roof to shed water which can result in leaks. Finally, the moss itself acts as a sponge which can cause conducive conditions for rot in the wood structure underneath. A simple application of a zinc or iron based fungicide in the fall is a proven method of keeping this stuff at bay.