The Hidden Dangers of Roof Moss

by Crown Roofing

Posted on December 10, 2017 at 9:00 AM

A roof with moss overgrowth can cause problems on the roof.

Now that winter rains are here in full now is the time roof moss gets going on the roof. Roof moss can certainly cause problems. Did you know about the hidden dangers of roof moss?

Crown Roofing recommends removing and preventing moss growth because of what it can do to a roof. As the moss thickens and grows on an asphalt shingle roof it can raise the shingles up allowing water to go under the shingles, causing the underlying plywood decking to rot and causing the roof to leak. 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 torn/blown off the roof.

It may seem that only wood shake roofing is vulnerable to roof moss growth, but this is not so. All types of roofing can harbor moss growth including composition and concrete tile roofing. Furthermore, the damage caused by moss growth is equally problematic for all kinds of roofing where roof moss has taken hold. You may see roof moss if it visible to you, but it may also grow in inconspicuous locations out of ordinary sight, especially in high shade locations areas where moisture is able to remain on the roof for extended periods.

Moisture feeds the moss and as long as there is moisture it will grow. There are various things you can do to prevent moss from growing on top of the roof. We at Crown roofing recommend:

• Keep the roof out of the shade by trimming up trees.
• Install zinc or copper strips at the top of the roof ridges.
• String copper wire across the roof at intervals.
• Keep the roof clean of debris on a regular basis.
• Roof Moss Removal
• Algae/moss resistant shingle installation.

(NOTE: Do not hammer the nails or place the screws through the asphalt shingle, always attach anything to the roof edge!)

If moss is a problem on your roof, you may want to take the time and effort to clean it up. For the DIY Homeowner, though, we strongly recommend a safety first approach with careful advance planning. Roof tops are steep and slippery, and falling is invoking a potentially unwanted life-altering event, so it is a good idea to develop a plan of action which includes safety protocols and advance purchase the products you are going to use before getting started. That will mean some advance research of the cleaning options available.

There are many products which can kill roof moss. These solutions may work for one person but not so well for another. We know of many products that actually do kill roof moss and are readily available from hardware, grocery stores or nursery supply stores. Bleach, salt, baking soda, copper sulphate solution and sodium hypochlorite (which is a powdered form of bleach used in the pool cleaning industry), for example, are inexpensive products that homeowners have used on their roofs. We would like to share a word of caution, though, to the DIY homeowner if any of these products are used. Care must be taken that these chemicals do not harm nearby plants and soil. Either consider laying down tarps or have someone assist you by actively spraying the affected ground areas with water while these products are rinsed from the roof.

Salt applied to the roof will kill moss. Bleach applied to the roof will kill moss. Baking Soda applied to the roof will kill moss. Copper applied to the roof will kill moss. Sodium Hypochlorite applied to the roof will kill moss.

One product we find valuable and recommend called Wet & Forget, is a proven product available from our your local Home Depot. It is quite easy to use and simply does the job it's supposed to do. The product comes with instructions and there are plenty of on-line instructions as well.

Wet & Forget applied to the roof will kill roof moss.

Wet and Forget

One customer wrote:

“I only ordered a half gallon of this product because I was skeptical that it would work as advertised. After applying it according to the directions I am now convinced that it actually does what it claims – i.e. removes moss, mold, mildew and stains from outdoor surfaces."

Wet & Forget is easy to use and there is plenty of information available to help get you started.

How To Use Wet & forget.

Regardless of the method you may use to kill roof moss, one thing is certain. Once the moss over growth has been killed it is going to end up in your gutter and will have to be removed so that the drains will not become clogged. Therefore, part of your moss removal strategy must include clearing and cleaning the roof drains and down spouts.

Moss Removal - What Not To Do

Your roof is an investment that must be safe guarded. Now that we have provided some advise on what to do about moss, we now would like to give you some “what not to do” tips when trying to remove moss from your roof.

First, do not pressure wash the moss off by using a high powered pressure washer to remove the moss. This will dramatically reduce the life of your roof from erosion of the asphalt shingle granules which help protect the shingles and ensure a long life of the roof.

Second, exercise caution with using strong acids, alkalies or salts to remove moss. If your mixture is too strong or stays on the roof too long, it can eat away at the shingles. Chemicals may also harm vegetation around the house. 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.

Third, do not scrape the moss off of the roof. This can rip, crack, and break the asphalt shingles themselves.

Fourth and final, If 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.

Thank you for taking the time to explore the issue of roof moss with Crown Roofing. We're here to help. Please do not hesitate to contact us for all your roofing needs!

Leave a Comment:


Roofing Talk December 10, 2017 at 9:00 AM

When I first started cleaning roofs from moss I used a mixture with sodium hydroxide and water. The water that would come off was a dark brown color. Now after having more experience in cleaning roofs I realize that this brown color was from the chemicals eating away at the asphalt shingles. I no longer use a sodium hydroxide chemical solution, but instead use chlorine to clean roofs from mold, moss, and mildew

Roofing Talk December 10, 2017 at 9:00 AM

I always rinse the roof after applying a bleach solutions. If it gets on the plants make sure you have a guy rinsing the plants with 100% water while a guy is rinsing the roof

More Roofing Talk December 10, 2017 at 9:00 AM

I use washing up liquid spread it along the ridge and let the rain wash it Down the roof. Job done.

Blog Search


Winter rains are upon us and now is the time roof moss will get going on the roof. Roof moss can cause roof leaks if you have an older roof and are not paying attention to what is growing up there.

Blog Main Menu