How to Clean Moss and Algae from your Asphalt Roof Shingles
By John M. Wickline, President
Algae and moss on roof surfaces are just plain ugly and detract from the curb appeal of a home. Some stains are simply just cosmetic concerns, but some stains, if left unattended, can lead to serious damages. No matter, you will likely want to eliminate these unsightly visitors on your roof. As a Home Inspector in Hilton Head, Bluffton, Sun City, and Okatie, SC, I see quite a few roofs with these ugly attachments.
What could be causing the stains?
Often discoloration is nothing more than shingle erosion on the roof shingles. Roof shingles that are older (approximately 12 to 15 years old) may start to lose surface granules from the shingles, resulting in a dark or black appearance on the shingles. It may be time for a new roof. Hopefully your are not going to have to deal with this problem. Now let’s move on to less expensive conditions that may be the culprit.
As a Home Inspector in the Hilton Head and Bluffton South Carolina areas, algae is the most common cause of discolorations that I observe. Algae, (sometimes mistakenly referred to as mold or mildew), often starts off as small black stains and spreads out over time. It is a cosmetic concern and not harmful to anything other than the appearance (that all important curb appeal). See Figure 1 for example:
|Figure 1 Algae on shingles JW Home Inspections, Inc.|
Inspecting homes in the Hilton Head and surrounding areas, I also find moss and lichens growing on roof surfaces. Soft green and velvety patches of moss, and lichens can both cause damages to roof surfacing (shingles and some other types of roof surfacing materials). Such growths often occur on roofs that are shaded by large trees overhanging and shading the roofs (common in Hilton Head). This is an excellent reason for keeping tree branches trimmed back from the roof, as well as blowing off the debris on roof surfaces. Such growths can actually lead to shingle erosion, as well as curling and cracking of shingles. Also some moss or lichen growths may be dense enough that they form water dams, and allow water to wick underneath the shingles, causing damages. See figure 2 for an example of moss, and figure 3 for an example of lichens.
|Figure 2 Moss on shingles JW Home Inspections, Inc.|
|Figure 3 Lichens on roof JW Home Inspections, Inc.|
OK, thanks for that information. Now what do I do about these ugly growths?
Glad you asked. If (and only if) you are comfortable walking a roof and take necessary precautions (ladder safety, harness as necessary, proper shoes, protective clothing and gear, etc.), then you may want to consider cleaning the roof surfaces yourself. If not, please hire a professional. Basically the procedure commonly used is to cover with plastic any plants or objects below the roof line (such as heat pump condensing units, plants, etc.) that may be harmed by a bleach solution. The bleach solution (50/50 solution of bleach and water) is sprayed with a garden sprayer onto the roof surfaces and allowed to set for approximately 20 minutes, and then rinse off with a garden hose (power washers can remove granules from the shingles and cause damage). You may have to get tough with some deposits by using a soft bristle brush on them, without scrubbing too hard. You may also have to spray the solution again and let is set for 30 minutes and rinse. Some staining may remain but will likely wear away with time and exposure to sun and rain.
OK, but how do I prevent these nasty growths from occurring or revisiting?
Please remain calm. There are effective preventive measures you (or a hired professional) can take. Zinc strips, (see figure 4) can be applied at hips and ridges to prevent or minimize these growths. Copper strips can also be applied (they will make your wallet seem lighter though). Both zinc and copper strips work by having rain fall on them, and small particles of the metals run onto the roof surfaces, thus protecting them like magic. OK, so I am not going to explain the physics behind this mystery, but it’s good to have a mystery in life now and again. If performing this magic act yourself, be sure to follow instructions that come with your strips (please note that I can’t help you in your strip search, you are on your own with that one). Also, as I mentioned before, keep the roof clean and remove tree branches (if possible) to allow more sunlight on the roof.
|Figure 4 Zinc strips|
It really is a job for a professional, since they have the experience and specialized equipment to do the job safely. However, if you insist on doing it yourself, keep safety in mind. It is definitely not worth falling of a roof, so only attempt this if you take all safety precautions. All it takes is one inattentive moment or one small slip, and you will be quickly introduced to Mr. Ground. He is a hard one, and very unforgiving, you can be sure. For information on ladder safety, you can visit the following link: InterNACHI’s article on ladder safety.
Once you get the lichen cleaned from your roof, you will be lichen the looks of your roof more and more. Sorry for that one.
Again, thanks for reading.
John M. Wickline, President
Serving the Hilton Head, Sun City, Okatie and Bluffton areas in SC