Jackson Contracting cleans roofs with black stains on them, which is an algae, including the moos and lichen. However, there are other times that a New Hampshire roof may have rust stains on them. The cause of this can be from a metal chimney on the roof that is rusting or a metal screen on top of a fireplace. There can be other causes like an air conditioner that drains on the roof or old metal drip edge that has oxidized and is rusting. This can create rust stain or even water that is high in iron can also cause a rust stain.