Most pressure washing companies that begin roof cleaning find that there is a considerable amount of technique and skill when cleaning roofs. Any contractor that performs roof cleaning should be aware of roofs are installed, failure to understand roof installation methods can cause thousands of dollars in damages from a pressure washing contractor.
Its imperative that the pressure washer use extremely low pressure to avoid damaging the shingles and that the roof is inspected prior to the commencement of the job. Remember, most pressure washers used in roof cleaning use a minimum of 4 GPM and as much as 10 GPM!. So it is easy to understand why knowledge of roofing installation and a roof inspection is necessary when you consider the amount of water that could enter the structure during roof cleaning.
Before hiring a roof cleaning company make sure they understand the basics of roof installation. It is also equally important that your roof cleaner know the other structures on the roof and their function to avoid causing leaks around them. For identification purposes, pictures of these parts can be found on our roofing page. Most roofing materials are installed over a layer of felt paper and in some cases a rubber like ice guard material. The first layer of shingles is called the starter course and is installed at the lowest point on the roof, upside down. This allows a solid base for water to run over without leaking down into the rafters and plywood between the shingles key ways. Once this layer is installed another shingle is place directly on top of it, and the rest of the roofing is placed in a similar fashion up the roof line. The reason shingles are installed in this manner is to allow the water to run over one shingle onto the next until it enters the gutter system.
If your roof cleaner can identify the common fixtures on a roof the next step is to identify what they will be cleaning from the surface. The most common reason for cleaning asphalt shingle roofs is to remove a fungus growth called Gloeocapsa Magma. This particular type of algae is air-born and will collect on any type of roof. In most cases the owner of the property won't notice the algae growth until it begins to take over large sections of the roof. This algae usually forms dark brown or black stains on the roofing and it thrives in mostly warm humid areas.
Roof cleaning with the appropriate cleaners can effectively remove this unsightly blemish from roofs fairly easily if you know how. Some manufacturers suggest using a mixture of TSP and Bleach to kill the fungus. Other manufacturers suggest using a sodium hydroxide based cleaner instead.
Regardless of which cleaner you use when cleaning roofs it's important that you check with the manufacturer of the roof to meet their guidelines. Some manufacturers will void the warranty on the shingles for one method but not the other. However, ALL roofing manufacturers agree that the use of high pressure should NEVER be used when cleaning roofs. Some specifications set the safe pressure range at 600 PSI but the best rule of thumb to use is. Use the least amount of pressure and the mildest chemical possible to achieve the desired result!
