A moss buildup on the roof causes more debris to get trapped on the roof. This debris traps water which makes the roof at risk of much more rotting and leaking.
For example, as the moss thickens and grows on an asphalt shingle roof it can raise the shingles up and loosen them. When the shingles get raised it allows water to go under the shingles causing the decking to rot and causing the roof to leak. The raised shingles also pose problems when heavy winds are present because they will catch the wind like a sail and this can cause shingles to be blown off the roof.
What Promotes Moss Growth?
• A shady climate.
• Acidic environments.
• Moss grows well on hard surfaces.
• Moss needs a moist/humid environment to grow.
How to Kill Moss
The black mold-like stains and streaks that appear on roofs, particularly light-colored asphalt shingles, is actually a blue-green algae.
You could replace all the roofing with new shingles dark enough to disguise the staining, or with shingles laced with copper granules, which are lethal to algae. But that would only make sense if the shingles were worn out.
The less expensive solution is to spray wash the roof with a mixture of water and bleach to get rid of the algae. Just be sure to wet your foundation plantings first, and rinse everything in clean water when you’re done. Plants don’t like bleach, and wetting them with plain water first protects them.
To keep the algae from coming back, insert 6-inch-wide strips of zinc or copper under the row of shingling closest to the roof peak, leaving an inch or two of the lower edge exposed to the weather. That way whenever it rains, some of the metal molecules will wash down the roof and kill any algae trying to regain a foothold on your shingles.
You can probably see this same principle working on roofs in your neighborhood. Look for chimneys with copper flashing; the areas directly below the flashing will be free of any algae stains.
The strips also work on roofs suffering from moss buildup. Just scrub it off first with a brush, then bleach as above.
Because moss grows well in shaded areas one way to remove it from roofs is to remove its shade. This can be done by removing trees, trimming tree branches to allow more sun to penetrate, or remove bushes and other type of plant life that may be blocking the sun.
This method of moss prevention and removal is highly effective but remember that it may be ineffective if the weather is often overcast and cloudy.
Make its Environment Acidic
There are many common household items that have a pH level at or below 4. These products are highly effective at killing moss. Using these products with a mixture of water or directly to the moss can kill the plant. Be aware that acid products erode certain types of surfaces. By diluting the mixture you can prevent unwanted corrosion.
Make its Environment a Base
Since moss grows in a pH environment of 5.0 – 5.5 or 6.0, by changing the environment to a base level it will effectively kill the moss. Below is a list of some common household items that are bases. By mixing these products with water or by applying them directly they can kill moss in yards, off of roofs, siding, decks, or other unwanted areas.
If your moss problem requires more than just a simple scrub, there are a wide variety of commercial cleaning solutions as that will get the job done. Just wait for the next cloudy day before you head out to the roof with your cleanser of choice—you don’t want the solution to evaporate too quickly. Keep in mind that both commercial and homemade spray cleansers can damage sensitive plants and discolor siding, decks, or pathways, so you may want to spread plastic sheeting below your work area before you get started.
Some popular cleansers include Wet & Forget, a spray-on product for removing moss, mold, and mildew; Bayer 2-in-1 Moss and Algae Killer, a potassium soap of fatty acids and inert ingredients that you mix with water and then spray on; and Moss B Ware, a 99 percent zinc sulfate monohydrate powder that can be applied dry or mixed with water.
Whichever you choose, follow the manufacturer’s directions for application; some cleansers should be rinsed off after use, while others specify to be left on.
How Not To Kill Moss on Roofs
Roofs are expensive and an investment that must be safe guarded. That being said, we want to give you some “what not to do” tips when trying to remove moss off of your roof.
Do Not Pressure Wash The Moss Off. By using a pressure washer to remove the moss you are going to dramatically reduce the life of your roof. The high powered water will remove the asphalt shingle granules which help protect the shingles and weaken the integrity of your roof.
Be careful with using strong acids to remove moss. If your acidic mixture is too strong or stays on the roof too long, it can eat away at the shingles. If your roof cleaning solution has not been tested previously, make sure you test it on some spare shingles before applying it to your roof.
If any water is used to remove the moss, do not spray the water at an upward angle. If you do, this can cause water to go under the shingles and leak into the house or rot the wood decking of the roof.
If you have any questions about moss removal or need someone to come look at your roof please don’t hesitate to give us a call.