While driving in your car you see other buildings with similar problems, so you know that the situation on your roof is not an isolated case.

What is it? The black stains that you see is a form of black algae, it is a living organism feeding off of your roof. It generally can only survive on the north facing roofs or on heavily shaded sections of your roof that is because the ultra violet rays from direct sunshine will kill the spore and direct sun light dries out your roof not allowing moisture to congregate. The exact opposite happens on the north facing and shaded sections of your roof. Moss, algae, lichen or any fungus needs three things to survive, air, food and water. We discussed the water source being on the north side or under shade, the food source comes from the shingle contents, if you have wood shingles the wood is the obvious food source, if you have asphalt shingles, then the limestone that is used as a thickening agent is the food source.

Can it hurt your roof? It is actually eating away at your roofing material, taking with it, years and years of roof protection. You probably have noticed an abundance of shingle granules in your gutter, this is due to the growth, eating, loosening and disguarding their food. Wood shingles roofs rot out long before expected because of the growth barrier holding moisture. Asphalt roof shingles thin out, crack and often become dislodged because the growth raises the shingles and pushes out nails.

Depending on your skills, time and financial situation, you could clean your roof yourself, replace the damaged roof shingles or look to a specialized roof cleaning company to do the work for you.

Having the roof replaced - this is the first option a home owner considers, mainly because a lot of people are un-aware that their roof can be cleaned, however this is a very expensive choice and may only temporarily solve your problem. "Algae resistant" shingles are new to the market but do your homework, they will only warrantee them for about 10 years.

Hire a roof cleaning company - Good choice but whom? They are around, usually listed in the yellow pages under "roof cleaning" or "power washing". What to look in a roof cleaning company is very important. 1. References 2. Specific insurance coverage, a painters, carpenters or any construction general liability policy does not cover roof cleaning, check it out 3. inquire about their cleaning product, there are a lot of products out there that will clean a roof but if they heavily chemical laden they will dry out the roof shingle to such a point that a few months down the road on a windy day, shingle pieces will be flying. These product will also stain the face of your home, kill plants and grass, you want them to use something "environmentally safe", not just "bio-degradable" that only means that eventually it will disappear, there are bio-degradable plastics available but you wouldn't want them laying on your lawn for the next 20 years, would you? So make sure the product is environmentally safe 4. Portfolio, they should have before and after pictures of jobs that they have done and you should take the time to drive by one of the homes and make sure that they didn't just download pictures off of the internet 5. Do they have a home improvement license? They should. If they cannot provide those 5 things, move on to the next company.

Clean it yourself - Dangerous work! But achievable if you consider yourself the "handyman" type and the most cost efficient solution. Buying the right product is the trick; don't even consider bleach it is a disaster waiting to happen buy a product specially designed for roof cleaning. Don't fall for the "just spray it on and nature will clean it" product sales pitch, that's BS, it might work but it would be years before it would be clean and you would have to keep reapplying it. No, there is only one way, get up there, stage the roof safely along the bottom even if it is walk able the roof will become incredibly slippery, spray the product on, usually through a "garden style" sprayer, take out a medium bristle scrub brush and scrub the infected area keeping the area moist while scrubbing then take a regular garden hose and wash it off, it may only become 80% clean at first but all the loose, dead fungus will wash off with the next rain.

When cleaning is complete, there is only one proven way to keep your roof clean forever, and that is by applying a strip of zinc flashing across the ridge of your roof. Examples of how well this works are everywhere, just look at any dirty roof and you will see clean areas underneath any metal objects that is because when it rains, metal ions flow off of the metal coating the roof below it, the ions in the metal will not allow fungus growth. Boat motors have zinc on them to prevent algae growth, the theory has been proved for years it is highly effective and zinc is cost efficient only costing about one dollar per foot. When buying zinc, you will need a product that is at least 3 1/2 inches wide, a rule of thumb is one inch for every 10 feet of roof below it, the wider the better. Keep safety in mind when cleaning, John Redihan