Removing Algae and Moss Off the Roof


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What is the best method to remove blue-green algae or moss from asphalt roof shingles?

Thanks
 
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I very seldom advise people to not do a project themselves but this is one item best left to the pros. Why? Because they have the proper chemicals and pressure equipment to do the job right without damaging the shingles. They will be able to do the job without killing all the plants and grass. Be sure to get references and preferably hire someone with several years experience.
 
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Hi,

Excellent advice Doug and it can even go wrong with highly reputable roofers. 30 years ago Bron and I replaced the entire roofs to our bungalow and two roomed rear extension. The main bungalow we converted to tiles but the extension we covered with Nuralite sheets these being semi rigid mineral fibre bitumen sheet material and thought we could relax. A short while later we returned home to find the Nuralite was now painted silver? A very well respected roofing contractor had got the wrong bungalow; we could have cried after all the work we'd put in; the Nuralite had to be stripped off and replaced; the contractor apologized and offered to do the job but we just accepted the Nuralite and we re-did the work. Typical of our bad luck.

A few years ago I bought a 120 bar Nilfisk pressure washer and this to me was a big boys toy it being my "light sabre" having blasted everything at ground level I thought the roof is looking shabby so I also blasted the roof tiles and what a tremendous difference this made; the amount of dirt removed was incredible but I definitely don't recommend anyone doing this because it could be highly dangerous; our's is a bungalow with a 12.5 degree pitch roof so I was safe to do the work. I didn't even try to pressure wash the Nuralite. Pressure washing shingles though would destroy them; I tried pressure washing the tarmac path to the roadside and it easily damaged the path so in your case Kemper100 I would do as Doug suggests and get the professionals in.

Kind regards, Colin.

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A big Scots Pine tree was overhanging the roof so I felled the tree but was left with this unsightly mess.

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It was backbreaking pressure washing the roof tiles but what a tremendous difference.

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The main bungalow roof tiled and the extension roof in Nuralite; pressure washing brought the tiles up like new; I also built the new chimney stack and added a stone arch above the kitchen window to replace a very rusty metal lintel. I DON'T RECOMMEND PRESSURE WASHING A ROOF BY A NOVICE IT'S MUCH TOO DANGEROUS.
 
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Don't make this harder than it needs to be. You don't need to hire a professional or roofer unless you have a lot of money or afraid to get on a ladder. I've done it on several roofs. Don't let anyone scare you. Your roof will not melt nor will exposed wood or paint. 50/50 bleach will not hurt anything except micro organisms and moss. Wear gloves if you don't like bleach water on your hands and clothes you don't care if get splashed by the bleach solution.

Solution: Get a two gallon garden sprayer ($15). Fill it with one gallon of regular BLEACH (<$2) and one gallon of water. Spray the roof on a warm day top to bottom. In minutes, the green moss turns yellow- brown. Moss is dead. Don't pressure wash or rinse. Let the rains wash the dead moss away. You will never know it was there after a few rains.
 
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I very seldom advise people to not do a project themselves but this is one item best left to the pros. Why? Because they have the proper chemicals and pressure equipment to do the job right without damaging the shingles. They will be able to do the job without killing all the plants and grass. Be sure to get references and preferably hire someone with several years experience.
Proper chemicals?! Just use a 50/50 bleach solution with a garden sprayer.
 
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Billy, that will work but you also run the risk of killing ornamental plants with the overspray and runoff. You can also cause discoloring of paints and stains. There are a number of unintended consequences to consider before beginning any job. You also have to consider that these are shingles and not tiles. Roofers just love do-it-yourselfers that weaken their shingles with harsh chemicals and then get up there and blow the stone layer off the shingles with a pressure washer.
 
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Ive
Billy, that will work but you also run the risk of killing ornamental plants with the overspray and runoff. You can also cause discoloring of paints and stains. There are a number of unintended consequences to consider before beginning any job. You also have to consider that these are shingles and not tiles. Roofers just love do-it-yourselfers that weaken their shingles with harsh chemicals and then get up there and blow the stone layer off the shingles with a pressure washer.
I done this at least 10 times on asphalt shingles, never had an unintended consequence. Actually, I learned this from a professional roof cleaner. If you want to win some, you have to risk some. Ornamental plants?! Get them out of the way.
 
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I'm inclined to go with Billy on this.
Such a solution will do little "damage" elsewhere....If you are concerned about the run-off damaging plants/grass, further dilute the run-off with additional water via a hosepipe in the guttering.
Shingles with a 30-year guarantee are unlikely to be damaged or even discolour with such a weak solution.
Natural sunlight is more aggressive.
 
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