Mostly, all shingle manufacturers make asphalt shingles with an algae-resistance warranty. This warranty can range from 10 to 15 years depending on the shingle you may have chosen. But what about moss build up? In a lot of cases clients will mistake moss for algae and algae for moss. This is only because the clients may not know which is which, and use the terminology improperly.
To make things simple, Algae is a discoloration that may appear on your roof, whereas moss is a build up forming on top of the shingles. Algae discoloration happens over a period of time once the shingle manufacturer’s algae-resistance warranty has passed. Shingles are manufactured with zinc and copper granules infused with the stone granules and adhered to the asphalt. When the weather takes a turn for the worst and it starts to rain, your shingles are actually keeping your roof clean and clear from algae. The chemicals from the zinc and copper granules continuously wash off, cleaning the roof in the process, until the chemicals have completely washed away. Depending on the amount of zinc and copper granules added to the shingle will determine the algae resistance warranty the manufacturer provides. A good example of this can be seen on many roofs right below a chimney. Next time you are driving around your neighborhood, take a look around for some older light-colored roofs. You may notice that on some of those roofs there will be a lot of discoloration of the roof shingles except for the shingles below the chimney. This is due to the chemicals that continuously wash off the lead flashing at the base of the chimney.
There really isn’t any cure or precautions for moss. Moss build up tends to happen on the roof when there is a tree directly above the roof shingles. This tree will constantly drop small amounts of debris onto the roof, such as dirt, leaves, etc. This debris will embed themselves in between the shingle granules. The tree that is dropping the debris also is keeping that area of the roof cool and moist, not allowing that area of the roof to dry as fast and keeping the debris moist, allowing growth. Once this growth has started its important to stay proactive in keeping the roof clean before it can cause damage to the shingles.
For many years contractors and home owners would go up onto the roof and power wash the moss off the roof. This method would work well, but damage the shingles in the process. If you ever try to brush or pick moss from a shingle, you will notice that when you finally get the hunk of moss off the shingle, you also have pulled shingle granules with it. When you pull granules from the shingles, you are in turn, damaging the shingle. So, when someone is on the roof with a power washer, pushing anywhere from 900 to 1600 psi, you could imagine the number of granules that are coming off with the moss.
The granules that are infused with the asphalt, that create your asphalt shingle, are the asphalts protection from the UV-rays from the sun. When your roof shingles are missing granules, the roof shingles will deteriorate quicker. The roof shingles will start to burn, curl, and not last their warranted period.
You can now purchase roof washing products from your local Home Depot, Lowe’s, or hardware supply retailer. These products usually connect right to a garden hose. You simply turn on the water and wash the roof down. These products don’t work as fast as power washing the roof, but it is a safer alternative. Roof wash products can take anywhere from one to four weeks before you see its effects. The chemicals in the roof wash products will slowly eat away at the moss until it falls off on its own. Do use precaution and read the instructions on all roof wash products. If your gutters drain into a garden, it is a good idea to redirect the direction of the water while you are washing the roof. You wouldn’t want to kill all of your beautiful plants.
As always, with any roof work, be extremely cautious while working on your roof. If you have any doubts pertaining to your capability to work on your roof, please call a professional. Paying a few hundred dollars to a licensed and insured professional is a lot cheaper than what your hospital bill may be.