It depends on the type of roofing material. If you have asphalt shingles, you should clean them every 2-3 years. If you have cedar shakes, you should clean them every 4-5 years. If you have a tile roof, you should clean them every 6-8 years. And if you have a metal roof, you should clean it every 8-10 years. If your roof is covered in moss or algae, it's recommended that you clean it as soon as possible to prevent the growth from spreading and damaging the roofing material. Moss and algae can cause roofs to wear out prematurely, so it's important to take care of the problem as soon as possible.

It depends on your roof's material. Check the manufacturer's recommendations. If you have a shingle roof, clean it twice a year - once in the spring and once in the fall. If you have a tile roof, clean it four times a year - twice in the spring and twice in the fall. If you have a metal roof, clean it every six months. And if you have a slate roof, clean it every year.