The picture in this post represents a common problem, especially prevalent in the southeastern US, that effects many areas of the world and North America. Algae builds up over time causing deterioration of roofing materials. Lighter colored roofs save energy by reflecting the suns ray back into the atmosphere, once algae takes hold, the roof is darker and can result in higher energy costs by absorbing the suns energy which can heat the interior.
The good news is, that, caught early, the problem can be solved without major repairs or replacement costs. There are several ways to alleviate the problem. One way is to spray down the roof with diluted bleach or chlorine. This is very effective at cleaning the algae but does have it’s side effects such as killing surrounding vegetation and not being so great for the environment, not to mention the smell, but if it’s caught early and one is on a tight budget, this can be done.
Another way to get rid of algae is to hire someone to pressure wash the roof, however if choosing this method be aware that there are strict guidelines to follow in accordance with manufacturers specifications and is generally not recommended, but can be an option if done properly. Make sure, if you go this route, you know the manufacturers recommendations and that the person you hire is qualified.
Of course you can just replace the shingles with algae-resistant shingles and have zinc strips installed both sides of the ridge, but sometimes, just because the roof looks bad, doesn’t meant it needs to be replaced. In any case, if you notice algae on your roof it is important to take care of it as soon as possible, in the long run, the short term costs of proper maintenance could save you thousands.