If you live in just about any english speaking country then chances are you’re very familiar with seeing moss and other green stuff growing on roofs.
Moss is great where it belongs- in the forest. Not on roofs. This is what one of my businesses does full time is roof and gutter cleaning and quite a bit of moss removal. This is everything I’ve learned from cleaning over 1,000+ roofs!
In this article, we’ll explore the different methods for permanently eliminating moss from roofs and other structures, and keep it off for good.
The Causes of Moss Growth
Moss is a type of plant that is referred to as non-vascular meaning it doesn’t have roots or stems like a normal plant and instead can absorb water and nutrients and nutrients through it’s “leaves”.
This allows it to grow pretty much anywhere and specifically in areas up north like in the Pacific Northwest, the United Kingdom and pretty much anywhere else that gets limited sunlight and lots of rain.
Rain and limited sunlight also are ideal environments for many types of evergreen trees which add the third element to an area that moss can thrive in; debris.
Trees shed leaves, needles, pinecones, branches and also themselves harbor spores of moss which can rain down and fall all over the place.
This is why in many areas you see the same types of moss growing on all of the roofs around because it came from the same trees and paired with debris, limited sunlight, and rain moss can start to grow in full force.
Why Moss Can Damage Roofs
If you’ve ever seen a sidewalk in the city you’ve probable seen it crack and be uplifted by the roots of a nearby tree.
The tree is searching for a better hold on the earth, nutrients and water and it will do anything to get it.
Moss is similar.
While it doesn’t have the same types of roots as a tree it can still grow up and into the shingles of a roof.
Much like a sidewalk this can cause the roof shingles to crack and lose their water resistance and allow your roof and home to be exposed to the elements.
Moss can also clog gutters and this can overflow and cause the sidewall of your home to get wet, moldy and needing to be replaced.
Not to mention moss loves being wet so like a natural sponge it holds water onto your roof for much longer than a clean roof and the whole point of a roof is to keep water away thus making your home safe and dry.
All told, having moss and other green stuff growing on your roof is not a good thing and needs to be addressed.
How to remove moss safely
Moss needs all three of the above mentioned criteria to thrive. If you remove or add any of those then you can start to break the cycle and keep your roof, sidewalk, or driveway free from this pest.
The first thing you should do is make sure there are no trees or branches directly over the roof or touching your home.
This is not only a breeding ground for the moss but it also blocks the sun and allows moss to thrive much better than when it is exposed to harsh sunlight (notice how you never see moss on the southern side of a roof).
Next you need to remove the bulk moss and debris on the roof. This is best done with a gentle nylon brush or broom as most of it should sweep off rather easily.
Some moss can be very stubborn but we will deal with that soon chemically.
Any moss that can be easily swept off should be taken care of first and then leaf blow the whole roof getting the rest of the dirt and stuff off the roof.
Make sure you are careful when you’re on the roof, use a rope anchor and harness if necessary or you can also get an extension pole and brush from the ladder.
The best moss remover for roofs
Moss loves to live in areas of typically a lower ph acidic range of 5.0 to 6.0.
This means if we hit it with anything more acidic than that (less than 5.0 ph) or more basic than that (higher than 6.0) we can give the moss a harder time growing and coming back.
The stronger we go the more we can kill the moss on the spot and prevent moss from coming back for at least 6-12 months.
That being said there are 4 primary moss killing and preventing chemical mixtures.
Soft washing with Bleach (sodium hypochlorite)
If you have the right tools and equipment this is the top way to clean a roof and prevent moss from returning. Basically we are taking a mixture of bleach (around 2% sometimes up to 6% SH) water and soap (surfactant) and washing the roof.
Depending on the mixture this can kill moss almost instantly and within a few months the moss will have dried up, turned to dust and fallen off.
See this roof that I recently revisited and did a yearly cleaning on. You can see that the stubborn moss had completely covered part of the roof but after spraying and some time is all gone.
Soft washing with Oxygen bleach (sodium percarbonate)
Similar to using normal bleach, Oxygen bleach is a bit more eco friendly and less harsh to use. This can be better if you live close to water and don’t want to worry about runoff or if your roof is a bit more sensitive such as a cedar shake roof.
Here you can use two methods. Option 1 is to simply apply the oxygen roof cleaner in its powdered form and wait for it to rain OR you can activate it yourself with a hose.
Option 2 is to mix ½ cup per gallon of water into your tank or sprayer and let it dissolve in 10-15 minutes.
You can then apply this directly to the roof and watch as the oxygen does its job and eats away the moss and other green stuff growing.
You can grab some of this roof cleaner yourself at my other website here.
Powder treatment with Zinc Sulfate
This is one of the more common methods of treating and preventing moss growth is with powdered zinc monosulfate.
This is the cans you typically see at Home Depot and works quite well to kill and prevent moss.
It is a metal and is a bit higher on the toxicity so if you’re concerned about environmental impacts consider the oxygen bleach or the Eco roof powder below but if you want to just treat and be done with it this option is great too.
Simply get your hands on some powdered zinc (also available on my website) and apply directly to the roof and wait for the rain to rinse down and do its work.
This typically works within a couple weeks and you can see the moss start to turn black and die.
I have yet to see the zinc powder completely remove the moss compared to soft washing so you still may have to get up there and manually brush the dead moss away but it will make it alot easier for you to do so.
Definitely more of a preventative measure. You can also brush the moss off while it’s green and then apply the zinc powder to prevent any future moss growth and kill the little bits left over.
Eco Roof Powder treatment
As mentioned moss needs to live in a ph range of around 5-6. Hence if we treat it with any assortment of more alkaline powders such as sodium bicarbonate (baking soda) sodium carbonate (borax) sodium percarbonate (spencers oxygen roof cleaner) or even most laundry detergents then you can stop the moss in its tracks and prevent it from growing.
This treatment isn’t as ideal to kill moss, it’s more of a preventative measure.
If you cleaned the whole roof well with the brush then this could be a solid pairing and we have used these quite a bit over the last few years. Maybe if we happened to run out of the other options and needed to run to the store and buy laundry detergent or baking soda just to add something up there to help chemically prevent.
Not the strongest but still better than nothing and if you are a homeowner you can absolutely use it if you just apply it more often throughout the year maybe every few months and you should be good depending on your area.
To recap
Moss is great where it belongs- in the forest. Not on roofs.