Shingles are made from 3 primary layers which work together to protect you and your home. They are a fiberglass, asphalt, and granules.
Fiberglass makes up the base of most modern day asphalt shingles today. This fiberglass matting holds the shingle together and gives it strength. Nearly all asphalt shingle manufacturers purchase their fiberglass matting from Owens-Corning, who also manufactures shingles.
Asphalt is what keeps the water out of your house. When a shingle is first put on your home, it is pliable and, in warm weather, soft. Asphalt is an oil based product, and as such, follows the market volatility of crude oil. There are different grades of asphalt, some being softer than others. For instance, your better contractors will use a specially made ridge cap shingle to go over the top of a roof, or where two facets meet. These caps are made from an asphalt that is nearly 20% softer and are made to blend.
Granules’ primary purpose is to protect the asphalt. When the asphalt is softer and more pliable, the granules grip, or stick into the asphalt better. As a shingle ages, the asphalt begins to dry out — releasing the granules. As the granules release, the asphalt has nothing to protect it.
Granules today are primarily a stone and ceramic product. Some manufacturers add copper sulfate to their granules in order to retard algae growth — a problem more common on the north side of homes in the northern hemisphere. As the sun traverses the southern sky, very little light is shed onto the north side of a roof and therefore, it takes longer to dry. The longer it takes to dry, the more opportunity that algae has to grow. By creating a core of copper sulfate, think of it as the yolk of an egg, surrounded by the ceramic shell, the copper sulfate leeches out over time, stopping the growth of algae for as long as the copper sulfate continues to leech out in sufficient quantities. This is why some manufacturers are able to offer a 10 or 15 year warranty against algae staining.
So does algae staining damage a roof? The short answer is no. It may be unattractive, but the staining itself is not a sign that your roof has been compromised.
Is it better to have a dark colored roof? Again, the answer is no. A darker colored roof may mask algae growth, but will heat up faster, hastening the drying out of the asphalt. When asphalt drys out, it develops cracks and microfractures — think of it as a dry creek bed. In addition, a dark colored roof will absorb heat faster, hastening the natural breakdown, drying out of the asphalt, and driving up your energy bills all at the same time.