What causes moss to grow on a roof and what’s the best way to get rid of it? — B.V.
Moss thrives in a damp, shady environment. For this reason, it often occurs on the north side of a roof — since it receives the least amount of sun — or under overhanging trees that provide shade. Over time it can cause roofing to degrade.
You can physically remove moss from your roof with a long-handled scrub brush if you’re careful not to overdo it. While a pressure washer can be used, the powerful jet of water could damage asphalt shingles. With either method, work down the roof to keep from lifting and breaking shingles.
There are also several chemicals on the market specifically made to kill moss. Diluted bleach will work as well, though the runoff can damage plants. Be sure to wear rubber gloves, protective clothing, and eye protection when working with chemicals.
To prevent moss from returning, cut back any limbs that overhang the roof, or install strips of copper or zinc along the ridge. Since the treatment for moss is similar to that for algae stains, refer to our article on How to Remove and Prevent Algae Stains on Asphalt Shingle Roofs for more details.
I have a black asphalt roof and have moss starting to grow on it and I have removed the tree causing the issue. I am concerned about using bleach on a black roof. What are my options or am I over reacting about using bleach?
I was told by our roofing supply co. NOT to use bleach because it would discolor our dark charcoal shingles. They recommended a number of solutions containing copper sulfate (which is plant friendly) and/or zinc (which they do not sell), as well as the ridge strips for prevention. Can you give me any formula or recommendation without bleach?
Using bleach is recommended by most shingle roof manufactures and the ARMA, (Asphalt Roofing Manufactures Association).
“The most effective method of cleaning algae and moss from a roof is with a 50:50 mix of laundry strength liquid chlorine bleach and water. Apply w ith a sprayer and allow the solution to dwell on the roof surface for 15 to 20 minutes, and then rinse thoroughly with low pressure water”.
Hello I have some moss and some black streaks, if the only thing I did is put installed copper strips on both sides of the roof cap, over time would that be enough to remove the existing moss and blacks strikes?
It should, but it would take a while. If you want to see quicker results, consider sprayer an algae and moss killer, like Wet & Forget, on the roof when you install the copper strips; or clean the roof using a TSP and bleach mix. Check out our article on How to Remove Black Algae Stains on Roofs to find out more.
can i use diesel oil sprayed on asphalt shingles
Eric why in the world would you want to use diesel fuel which would be toxic to the environment not to mention flammable? Haven’t you seen what oil spills do? Please do not use any kind of oil or gas.
I have been aware of the copper strip solution for a long while but never dared do it for fear of attracting a lightning strike does the strip be fixed continuous or with breaks
While metal, such as copper or zinc, conducts electricity, it doesn’t attract lightning, and installing a strip of metal near the peak of your roof to kill algae shouldn’t cause a problem if lightning should strike. If it did, metal roofs wouldn’t be allowed.
What is the best way to remove moss of Terracotta Roof Shingles?
I have a flat roof with moss on it amongst the peddles that were there to protect the roof. Can I pick it off or would you recommend treating it with a bleach
Hello. We had a contractor install the zinc strips and it did not prevent the growth of lichen or moss. The cost was well over $500 and we are unhappy with the results.
When should one apply the bleach solution? After a rain, early morning, or evening?
I have killed all the moss on my roof, but it leaves these crusty clumps of dead moss. I am scraping them off with a plastic tent spike. Am I damaging the shingles? They will not sweep off. Any suggestions???
For removing moss clumps, a retired roofer in my church recommended using a garden rake!
Turn the tines UP so you don’t damage shingles, work from the peak down so you don’t lift shingles. The rounded back bar on the rake rides easily down the shingles but knocks the moss loose.
Thanks for the suggestion to use the back side of a lawn rake. Worked great. Followed up with a rounded stick (piece of a cedar shake so soft wood and thin). Then swept with a nylon bristle (softer than straw) house broom. Was easier than I thought it was going to be, but still work of course. Thanks again. B
Great advice all! So where do you get copper/ zinc strips? How large? What size? I’m going to attack my roof next week using bleach solution with fingers crossed…
I mixed a strong solution of ferric sulfate crystals (moss out for lawns) and hot water and a few drops of liquid soap. I let it cool so it precipitated out, then mixing the remaining solution half and half with water and sprayed it on my composite roof/moss. Seems to work for small patches- but will it damage composite??
Hi, I have moss on the roof of the house. We have been in the house for 23 years and nothing like this had happened before. I haven’t seen any changes, there is no trees branches. That part of the house where the moss is, there is no sun. Can you please tell me how we can fix the problem? We had the shingles put on 5 years ago.
I bought shingles that were supposedly moss resistant and a good quality. I put the zinc strip along the top ridge from end to end, and I still have moss in areas. I think bleach is going to take care of it, but the shingles are brown. Hope they don’t streak and i’m gonna try the rake, too. Let u know how it works.
Baking soda and warm water solution will kill roof moss.
Is October to late to apply a moss removal solution in a frost free climate?
Can I use weed & feed or sharp sand to get rid of moss on
my roof. Ithink it would be easy to throw one or the other over my
I used Tide – white powdered laundry detergent after trying metal strips, Moss Killer , etc . A hand cranking spreader worked well but apply lots . After 1 month all the moss was dead . Then I scraped the dead moss off .
Thanks for whom ever said Tide is best !! Colin in BC ‘s Okanagan .
Re: chlorine bleach and plant life
It’s not so much that the chlorine kills the plant, chlorine has an incredible need for electrons to be stabilize its outer ring of electrons. And it easily gets the electrons it needs from oxygen.
Unfortunately, the microbes that live in the soil have a need for oxygen too. They have a symbiotic relationship with plants (think of sharks and those wee hanger-on fish the shark never eats). The microbes kinda pre-digest minerals like Nitrogen, Phosporus and Potassium (N-P-K, the 3 numbers you consider to decide which box of fertilizer has filler and which is more worth the money).
The microbes have to be in the soil (so that’s why you add manure and Mykorhiza) and the baby roots and the microbes come to hang on to each other. The microbes give the nutrients. The plant gives them the sugar it makes.
So … No oxygen, no happy microbes … No happy plant.
I think the idea of super watering the plants beforehand is to dilute the impact the chlorine has on your soil. Up on your roof or sidewalk you need it strong to kill the moss/weeds … but so the trickle-down doesn’t kill the gazillion microbey pals you so, so want in your soil.
Apologize to your microbes by putting some manure about (say 2-3 times the amount you think is enough). Cow, chicken, sheep … It’s all like kefir or yogurt for your plants, with different microbes in their different guts. And water that in well so it trickles down and counters the plant-killing nature of chlorine. (The funny thing about adding manure … The soil level always seems to stay the same. …, not like adding a pile of pebbles which don’t break down.
There. That’s my bit, my pay-it-forward for the day. Get the moss … Save the plants.
Oh … I used a hose… And blasted it. Used my fertilizer sprayer ($20 at the big box). Having now learned about the bleach, I will do it again a few times more with some bleach-y-poo for the roof moss. And catch the gutter run-off.
. . . Got an office plant or such. … Throw your cold coffee on it … The milk will contain nutrients (vitamins, minerals and sugar). And … Feed the microbes!
I keep having to clean my gutters due to moss from the roof tiles , as I live on an estate with all houses built the same and of the same age my house seems to be the only one that suffers from excessive moss on the roof . The only difference is that I haven’t bothered to install additional loft insulation as recommended by energy companies . Is it possible that the lack of loft insulation is allowing heat to warm the roof tiles and encourage the moss growth ?
I’m 56 years old and i’ve never seen moss on roofs and mold on houses before. In the last 5 to 10 years it seems like everyone is having these problems. I’m thinking its a sign of poor installation or material that we believed to be name brands. Never seen this growing up. Even on 100 year old houses.
I would not use bleach on a roof – unless you get the mix right, you could be doing major damage. Also, power-washing is a no-no, you are removing the ‘grit’ from the shingles and again lower your roof life.
I am trying Baking Soda, as it seems to make the most sense. I’m trying a smaller section on a porch roof, that has started to show moss – not too much, but want to get a handle on it. The roof is 7 years old, asphalt shingles, no tree’s. I have applied the Baking Soda (Arm and Hammer) dry, basically giving it a good, liberally applied ‘dusting’. I did this today.
Going to wait and see what the result is after a few days. (moss should start to turn brown and die). But from what I’ve read online, it should work. The added bonus is that it is environmentally safe – does not kill plants or hurt birds. It’s definitely worth a try for that reason alone.
I converted a quite large telephone exchange into a two bed house, with extensions.
One of the things I noticed about the old building was a wide strip of roof that looked like new, after studding this for a time I realised that one of the telephone copper lines was about 3 M above the roof, and was the cause.
I would have to guess but I think it was there from day 1, we tried to establish how old the original building is but all records are archived in London, and we have yet to explore that avenue, at a guess 1950 ish.
I use rain water recovery so don’t want to jeopardise the porcelain with copper colours, a friend in the US has a lot of trouble with iron in the water, it destroys all the sinks, washing machines and loos by making everything below the water line bright RED, he lives in a conservation area and it has it’s own well, no mains.
I use washing up liquid spread it along the ridge and let the rain wash it
Down the roof. Job done
I have lived in this house for 15 years and until the last 18 months there was moss on the house and garage roofs, it is now turned black and coming off the roof. I have not treated it in and way. Why has it died ?
The easiest and cheapest way to kill and prevent moss/algae is by using a copper sulfate solution. You can find copper sulfate at stores like Lowes and Tru-Value Hardware being sold as root killer (dries out the roots so they break away from the sides of the pipe). You dissolve the crystals by suspending them in water (1 gal per 16 oz.) Then add that to 15 gal, of water with 1/4 cup of regular Ivory Liquid dish washing detergent . MIX WELL! I use an drill motor with a paint mixer set on slow and rigged up so I don’t have to hold it for 20 minutes. Do some math and mix 5 gal. at a time. It’s applied with a pump-up garden sprayer using 1 gal. per 100 sq. ft. so your basically wetting the roofing (enough to look wet and not just dampened). Do the entire roof. Existing moss will turn brown, go to rot and eventually get washed or blown off. Once it’s doing that then you can use a broom to sweep off what’s loose then leave the rest alone. Algae and black stains will eventually get washed away by the rain. The copper solution is absorbed like stain then is slowly leached out by moisture to eliminate any remaining growth and spores. By treating the entire roof the released copper can run down from the ridge to the eaves. the dark algae feeds on calcium carbonate that’s leached out of the granules so you can’t do anything about that. Moss and green algae require dead organic matter for nutrients so you can prevent their growth by blowing off the shingles to remove junk from trees that tend to accumulate between the tabs. You can apply the copper solution to new roofs to prevent any growth for a number of years. I just wait until some black stains reappear then fail to disappear after a few rains. The crud only needs humidity levels of 75% or more (dew) to grow so can develop during dry spells. Bird dropping will often contain their spores plus calcium carbonate and will create the black spots that’ll have dark streaks below them (cause by their released spores running down the roof). The new stains will disappear if there’s sufficient amount of copper being leached out from above. If not, then that’s your cue to retreat the roof. The same black crud on the rood also grows on your flat concrete so might as well get rid of that, too. I use 10% sodium hypochlorite (pool shock) mixed with 2 gal, of water and TSP substitute (8 oz. per gal.). Sweep off the dirt & debris then wet the surface @ 100 s.f. per gal, then let it dry. The bleach solution reverts back to brine (salt water) within 15 minutes and the TSP substitute (usually sodium metasilicate) will bond to the cement. The both will kill off any remaining growth and spores when dampened again and the TSP sub will provide a residual effect to deter regrowth until eventually being leached out. If you have a pressure washer then wet the surface using a bleach/liquid laundry detergent solution, let it set for 15 minutes before spraying off. Once dry then apply the TSP sub to deter regrowth for awhile. You can use any of the above on funky masonry and stone.
I have moss on my roof maybe from an oak tree that was removed last year so I am guessing once I have it removed the moss won’t return. Who can I hire to remove the moss-a roofer, carpenter-I won’t do it myself. I am reading how to prevent roof leaks-it isn’t as thick as the pictures show. Any advice is greatly appreciated,
Use Sodium Percarbonate its a granule which produces oxygen when mixed with water. This breaks down the rhizoids (moss roots) and kills the moss. It also kills the spores which enables the moss to spread. It doesnt harm plants or grass so it doesnt matter if there is run off from the roof.
In the UK we get lots of moss on roofs! Either sprinkle the sodium percarbonate on the roof when its raining or wet the tiles down with a hose pipe and sprinkle it on by hand. It cleans the roof too.
I am a home inspector in Salem Oregon and I see a lot of asphalt roofs and moss in the course of my day! I have two things that I want to warn people about…using detergent (Tide or Dawn) and using power washers to clean an asphalt roof. Both work really well at cleaning a roof and shortening the life of the roof. I have seen too many 10 year old roofs which are ready for replacement and whenever possible, I ask what was used to treat the moss, and in most cases, Tide is the leading culprit. It is a degreaser, as is Dawn, and your asphalt roof structure is just hardened grease! In these cases, the granular surface is largely gone and half the roof life with it. Power washing is also too aggressive for an asphalt roof and I have seen the most amazing “flight of the bumblebee” patterns cut into a roof surface by a 0 degree nozzle and a few beers! Again, many years of roof life are lost to power washing. In my experience, kill the moss, let it die, and in a few weeks manually remove the dead moss with a soft cedar shingle, It’s not easy, but it works. Letting the moss slowly roll down your roof and into the gutters just clogs up the gutters, downspouts and underground drains. Dead moss also acts like a sponge and soaks up more moisture…the dead moss must go! Remember, for an asphalt roof, it’s all about the granular material protecting the asphalt shingle, and when the granular material starts to leave, it’s time for a new roof!
When is the best time to apply a moss killing product, the Fall or int he Spring?
Late winter or early spring is an ideal time to kill moss. You don’t want that moss to make it to the spring growing season and, worse, to spread before summertime.
Hi … any suggestions about removing moss from a flat roof at our local cricket club .
The moss is on top of a covering of stones which in turn cover ashfelt on plywood.
Rock salt was suggested to me but someone says it may damage the ashfelt …!!… any suggestions?
Please do not use bleach on any roof.My neighbour did..sprayed it on his cedar roof,and I guess there was some wind?He killed my 2 apple trees,several Maple trees,and many plants.I breathed it in and so did my cat..cat got sick and I ended up with permanent lung problems..think about the environment.
Moss on roofs is a common problem here in the UK. The other thing to be aware of is that it actually fills cracks & when you remove it, tiles can settle out of position and/or expose cracks/breakages.
I was told to use zinc strips when I got a new roof.
Hi, Dee. Zinc strips work for us, but results do vary with each application.
Need help removing moss, mold, mildew and algae? Try Wet and Forget Outdoor.
Happy home improving! 🙂