There are a wide variety of things that can end up leaving nasty stains on your roof. Two of the main culprits are algae and lichens. They feed off of organic matter that is trapped in the shingles and end up eating the roof. Left to their own devices, they can be capable of causing considerable damage. If you are worried that this may be happening to your roof, below are some roof cleaning methods you can use to get rid of those unsightly stains.
The Eco-friendly Approach
This method does not use any bleach and uses low pressure to get rid of algae and lichens. Companies that use this method will employ eco-friendly products that don't contain any toxic chemicals like phosphates and and the aforementioned bleach, which are capable of harming and killing vegetation and polluting waterways. This method also uses a low-pressure rinsing system, which avoids the damage done by high pressure washing and brushing.
The advantage of this method is that the effect is immediate and the algae and lichens are gone once the company leaves. The disadvantage is the products that they use cost extra, which you will end up paying for.
In this method, contractors will apply a mixture of chlorine bleach and phosphates to your roof and then wait for it to dry. It may need to be reapplied several times as needed. Any stains, algae or lichens that don't come off during the first application may end up being shed off once your roof receives a good rain, or potentially several bouts of rain. The bleach method is less expensive than the eco-friendly approach because the chemicals are cheaper, but the runoff and spray is capable of causing damage to surrounding plants and waterways.
High-pressure Power Washing
This method is generally the least effective way to get rid of stains caused by algae and lichens. The high pressure can be incredibly damaging to shingles and the root structures of these organisms are usually left intact, meaning that the results are usually superficial and temporary. Algae and lichen, given enough time, will return in full force and the problem will be just as it was.
Stains on your roof are not just a cosmetic problem; left untreated, the algae and lichen can actually do structural damage to your roof. If you want to get rid of algae and lichens and the stains they leave on your roof, consider either the eco-friendly or the bleach method, but keep in mind your impact on the environment.