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Ask a Pro: Is Moss on My Roof Harmful?

Posted January 16, 2020 by Patrick Morin
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As a Portland homeowner, it’s likely you’ve found yourself wondering, “is moss on my roof harmful?” The short answer is yes. Moss on your roof is harmful. If left untreated, moss can decay, shift or disintegrate your roof over the course of time. With the right professional help and guidance, you can make sure that moss maintenance and roof care becomes hassle-free.

Why Do I Get Moss On My Roof?

Chances are if you have moss on your roof, where you live is a big facilitator. There are four determining variables that create ideal living conditions for moss growth. This growth can be seen in a series of steps.

Dirt on the Roof 

It begins with layers of dirt that have settled atop your roof. Dirt’s texture also makes it easy for it to build up small pockets of itself in the nooks and crannies of your shingles.

Leaves & Dead Plants = Fertilizer

Just when you thought a dirty roof was bad enough, in comes the catalyst of moss growth: dead plants. Chances are, if you have moss growing on your roof, you live in an area populated with trees or lush vegetation. Should dead leaves/plants settle on your roof over a layer of fresh dirt, it creates the perfect breeding ground for growth to occur. 

Moisture (Humidity/Rain)

So now you have a layer of dirt and natural fertilizer on your roof. Now in comes the rain/humidity. Most times, without realizing it, many roofs become 3/4ths of a garden in these conditions. You’re probably thinking, “Now all it needs is sunlight.” Unfortunately, that’s not the case.

“No Sunlight, No Problem” – Moss Growth

While it is photosynthetic, moss only needs moisture to germinate and mature. Often times, their ideal environments are shaded areas. This is because moss use filaments to draw out their nutrients. Their roots act more like an anchor. (i.e the spaces in between your roof shingling.) 

Three Types of Roof Moss

While there are many different species of moss, there are three prevailing types of moss that often slowly encroach on homes. Over the course of thirty-four years, the professionals here at Roof Life of Oregon have been able to distinguish these three types of green troublemakers.

Roly-Poly Moss

A type of moss that grows underneath the shingles and begins to lift them off their mastic strip. They tend to grow at the ends of asphalt, shakes and tile shingle roofs. It is bright green in color and can appear to glow at times.

Spindly Moss

A moss that is harder to spot. Tends to become rooted in the shingle and eat away at it. This type of moss can disintegrate a shingle if left untreated. 

Furry Moss

Mostly seen on wood roofs and occasionally on a tile roof. A distinct characteristic is that it usually grows leaves along with it. This moss is different as it is growing on rotting wood, meaning your roof has wet rot. 

Does Moss On A Roof Cause Problems? (What kind?)

Different types of moss can cause different problems. At the end of the day, moss on your roof is something that requires professional attention and help. Aside from the different types of moss, there are other symptoms that come with such growth.

  • Moisture
    • Moss is quite literally nature’s sponge. It’s absorbent nature often leads to rot and moss growth. Taking preventative measures to ensure the growth stops before it begins will save your roof and you from a headache.
  • Growth
    • Under the right conditions, moss can grow substantially over the course of six weeks. Given that mosses draw their nutrients from filaments, and not their roots, they do not need the sun. Wet and shaded areas are ideal for moss growth.
  • Leaks
    • Untreated moss will cause leaks around your home. In this case, moss can shift your shingles, absorb moisture and then ruin the integrity of a roof. Such damage can come in the form of thin spots, holes and eventual leaks
  • Pests
    • Moss is a pollinating plant that can only reproduce in wet conditions. In these conditions, mosses produce scents that can entice microscopic insects. This, along with its lush vegetation promotes insect habitats for worms, spiders, and mites
  • Weight
    • Given its fast-paced growth coupled with its absorbent, the combined weight can over-encumber your home roof. This can lead to hundreds of additional pounds and cause ceiling damage/leakage.
  • Curb Appeal/HOA
    • Having moss adorn your roof is not exactly pleasing to look at. By having professionals from Roof Life treat and temper your moss growth, you will see your home in its true form!

Roof moss comes with a number of problems. However, taking the proper steps to ensure the health of your roof will save you on eventual time, stress and money. With that being said, treating your roof moss as a Do-It-Yourself project is dangerous and poses serious health risks. Many resources refer to using “home solutions” to combat moss growth. However, without the help of a professional and the right equipment, there is a chance that you can do serious damage to yourself and your roof.

Why It’s Best to Have Moss Professionally Removed (DIY vs Professional)?

As mentioned before, moss removal is incredibly dangerous. The conditions that surround rooftop maintenance should not be attempted by anyone without sufficient knowledge in roofing and experience in removing moss. Moss is very slippery given its high-water retention. This poses a great concern to those who are not properly equipped and experienced. Having the right chemicals and tools is an essential part of effectively removing moss.

Don’t Do It Yourself!


Some DIY solutions included bleach, vinegar, dish soap, and pressure washers. However, most, if not all of these ingredients pose more harm than good. Certain materials contain corrosive/degreasing properties that begin to loosen the asphalt coating built beneath the actual roofing granules. 

To further illustrate why DIY solutions are not advised, here is a list of popular solutions accompanied by their effects on your roof.


Chemical combination can cease moss growth. However, this comes at the cost of the bleach drying out a shingle roof. This causes what’s known as “curling” effectively shortening the roof’s lifespan and uneven shingles.


While vinegar has shown promising results in killing and eliminating moss, it tends to degrade the overall integrity of the shingles. This is due to the face that vinegar holds a pH level no greater than 4.5. White distilled vinegar usually measures around 2.4 pH. To put it into context, human stomach acid average pH levels range from 1.5-3.5 pH. 

Dish Soap

Dish soap is a degreaser. This is the direct enemy of any rooftops. As mentioned previously, your roof and its shingles are layered on a foundation of asphalt. Asphalt in its crude form is tar. Should the soap come into contact with the asphalt, you risk ruining the foundation of the roof itself and causing the shingles to slide in and out of place.

Pressure Washer

The usual pressure washers/attachments sold at your local Home Improvement store are not often suited for rooftop maintenance, especially against stubborn moss. Pressure washers often spray water in the range of 1,300-2,800 psi (dependent on gas or electric models). These psi levels along with its limited area of spray can puncture your roof, saturate the roof base and cause extensive damage to your home.

How Roof Life Removes Moss

The damage to both DIYers and rooftops cannot be understated. Making sure that you have qualified professionals with more than thirty years of experience and proven results will not only preserve the look and feel of your home but also save you from stress in the long-run.

After years of experimentation, tinkering and figuring out what works best, Roof Life uses a variety of different tools and strategies to combat the moss that plagues your roof. A few instruments used include a proprietary water hosing unit which produces enough total volume to sweep a vastly infected area, while simultaneously using enough pressure to wash off the moss build up. This in combination with other services such as “Self-Cleaning” and “A Gentler Method” has stood the test of time to ensure customers get the highest quality clean. To top it all off, Roof Life holds an exclusive license in the use of Dennco Chemical Co.’s patented shake, composition, and tile preservatives. Ecologically-friendly, non-toxic and highly-effective at extending the life of your roof!

Moss Prevention Tips

With all this information in mind, it is worth noting that homeowners can take necessary precautions to ensure that moss/debris build-up is kept to a minimum. Although we advise against DIY treatment, there are a few preventative tasks you can do to maintain roof health and appearance. A few things you can do to prevent moss/debris growth include the following.

Pruning trees

A preventative measure that goes a long way in ensuring that any residual dirt on your roof gets no fertilization. Pruning surrounding trees and clearing its dead branches/leaves/twigs will give the option for the moss to begin its growth

Clean Gutters

A lot of excess debris can create clogs in your gutter, creating an overflow. This may very well carry water and nutrient-rich plants to fertilize and facilitate plant growth. Regularly cleaning your gutters ensures proper drainage and peace of mind from the build-up.

Regular Roof Inspection (from the ground)

Treading a house roof is dangerous and potentially fatal. Walking around your home and assessing any apparent damage from the ground is advisable. If you suspect any problems with your roof, call Roof Life! We offer free roof inspections. 

In summary, there is so much more that goes into roof inspection/cleaning than one would suspect. Thankfully, we here at Roof Life are happy to take the guesswork out of your hands and are prepared to help you in any way that we can. With over thirty years of industry experience, we know a thing or two about moss/debris types, roof life, proper maintenance, and customer satisfaction. To learn more, please call us today or request your FREE well-care roof inspection!

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