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How to Clean and Prevent a Mossy Roof | Ask This Old House

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By Quentin Peters
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Ask This Old House general contractor Tom Silva helps a homeowner remove moss from his roof and prevent it from growing back.

#ThisOldHouse #AskTOH
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Time: 2-3 hours

Cost: $100

Skill Level: Difficult

Tools:
Safety harness system [https://amzn.to/2H2hhEC]
Push broom [https://amzn.to/384lpQh]
Hammer [https://amzn.to/31Dzi5S]
Caulking gun [https://amzn.to/2OyLLlN]
Garden hose [https://amzn.to/2usm27I]
Rubber gloves [https://amzn.to/3baakiG]

Shopping List:
Zinc strip [https://amzn.to/2Sk9asm]
Roofing nails [https://amzn.to/39hNdRp]
Roofing cement [https://amzn.to/2Hcyonz]
Pump sprayer [https://amzn.to/2OyBIgA]
Bleach [https://amzn.to/3bffNEY]

Steps:
1. Start by securing the harness system to the roof, following the manufacturer’s instructions to ensure they’re installed properly.
2. Using the push broom, lightly sweep the roof to get off as much of the loose moss as possible.
3. Install a zinc strip near the ridge of the roof. When it rains, water will pick up the particulates in the zinc and deposit them along the roof, preventing more moss from growing.
a. Roll out the zinc strip underneath a course of shingles, allowing roughly half of it to be exposed and the other half underneath the shingles.
b. Nail roofing nails about halfway through the zinc strip, just to get it held in place.
c. Apply a bead of roofing cement around each nail before nailing them all the way through. This will help seal up the hole made by driving the nail.
d. Once the nail is all the way through, add another bead of roofing cement on top of the nail.
e. Repeat this process for all the nails.
4. Below the roof, spray any plants or grass with water to protect them from any runoff bleach that may fall off the roof during the next steps.
5. In the pump sprayer, pour a mixture of roughly 1/3 a gallon of bleach to 1½ gallons of water.
6. Spray the bleach mixture on the roof. The bleach will kill off any leftover moss over the next couple of days.
7. Remove the harness system from the roof.
8. Spray any plants and grass underneath the roof with water again once the process is completed.

Resources:
When working on a roof, safety is very important. Tom added a roof anchor [https://amzn.to/2S3D991] to the rafters, wore a harness, and used a safety line [https://amzn.to/2OzVZCx]. These can be purchased at home centers or hardware stores.

Tom used a push broom to gently remove the loose pieces of moss.

He then installed a roll of zinc strip moss preventer, which can be purchased online or at specialty retailers.

Finally, he sprayed down the roof using a solution of water and bleach. He started at the bottom of the roof and worked up so that he wouldn’t step on wet areas and slip.

About Ask This Old House TV:
Homeowners have a virtual truckload of questions for us on smaller projects, and we’re ready to answer. Ask This Old House solves the steady stream of home improvement problems faced by our viewers—and we make house calls! Ask This Old House features some familiar faces from This Old House, including Kevin O’Connor, general contractor Tom Silva, plumbing and heating expert Richard Trethewey, and landscape contractor Roger Cook.

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Keywords:
This Old House, Ask This Old House, DIY, Home Improvement, DIY Ideas, Renovation, Renovation Ideas, How To Fix, How To Install, How To Build, Tom Silva, roof, moss, cleaning, prevention

Watch the full episode:
https://www.thisoldhouse.com/season-18-ask-toh-episodes

How to Clean and Prevent a Mossy Roof | Ask This Old House
https://www.youtube.com/user/thisoldhouse/

(Visited 1 times, 1 visits today)
7-10 minutesAsk This Old HouseAsk This Old House general contractorCleaningcontractor Tom SilvadiyDIY Ideashome improvementHow To BuildHow To CleanHow to Clean and PreventHow to Clean and prevent mossy roofHow to Clean mossy roofHow To FixHow To InstallmossMossy Roofmossy roof cleaningpreventionrenovationrenovation homeRenovation IdeasroofThis Old HouseTom Silvatom silva framingtom silva interviewtom silva this old house

About The Author

Quentin Peters

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Comment (0)

  1. I spend the money and get a tube of Through the Roof. You can put a shingle down permanently even on a wet roof. On a new roof, the face nails, I seal then grab some loose roof grit and drop in the sealant to help hide it.

  10. How about Roundup?
    "I noticed green algae on my small shed's roof, and while it looks very nice, I figured I could quickly remove it from the ground."

  12. I have being a fighter from the beginning and it has being a very rough journey for me having herpes virus, cold sore and shingles and I am so grateful to God Almighty for helping me find Dr Madida on YouTube whom by his herbal treatment cured me in 21 days

  14. On my house, due to a walk out basement, the back of the house is 3 stories up. When I work back there, I put on a harness and I run the rope over the peak to the hitch of my truck parked on the front side of the house. It takes pretty careful measuring to make sure that, with the length of the rope, the truck is positioned correctly to not allow me to hit the ground. Better than putting nails through the shingles.

  18. I also add Dawn dish soap to my chlorox/water mix to help the water be a better surfactant. I use a container with my solution that attaches to the end of my garden hose, not too harsh, to blow off moss instead of the aggressive scrubbing action they did. PS, I've worked on roofs for years and I've never installed a safety harness. Proper shoes and care, and you'll be fine.

  22. I have A LOT of moss on the roof of my shed/shop here in CT. I put in a wood burning stove a little while back and used galvanized pipe to secure the stove pipe to the roof. There are two perfectly clean strips running down the roof starting where the galv pipe is secured. Now, the moss free strips don't run down all the way to the gutter, but maybe 6' down. And the galv pipe is an old soccer goal post and it's, what I'd say, heavily galvanized. I think if I'm going to do this zinc strip thing I'd want to find galvanized strips that are more heavily coated than the stuff they're doing in the video. The concept DOES work though, and that's cool.

  27. helpful video. I've been a climbing instructor for over 25 years. it might be helpful to mention that bleach on your rope and harness will degrade the material and shorten the usable life span and weaken the rope. If you do get bleach on your rope, rinsing the rope will help. the worst case would be repeated exposure to bleach without any cleaning. I hope this info helps somebody out there stay safe on their roof

  33. I'm watching everything you all put out about roofing because some shingles blew off during a storm and this video answered all my questions about the safety harness! Could you make a video about all that outside of the moss removal video? Love your show!

  36. The only problem with zinc and copper is that they are toxic to fish and other aquatic life. When it rains, the metal leaches into the rainwater in very small amounts, and the polluted rain water ends up in our streams and rivers. In the Pacific Northwest we have a lot of moss, a lot of rain, and a lot of very endangered salmon that live and reproduce in our urban streams. But luckily there are alternatives to metal strips: a sprinkle of baking soda kills moss very effectively, and is not harmful to the environment. Just re-apply when you get your gutters cleaned; works like a charm. Thanks for doing your part. 🙂

  37. I too am familiar with the "supermoss" in the Pacific Northwest. I use Wet and Forget 10587 1 Gallon Moss, Mold and Mildew Stain Remover once a year and it keeps my roof clear of moss. It is just as effective as bleach and it lasts longer. It's also environmentally safer and won't harm your landscaping flora. I buy it from Hardware Sales because "Amazon….."

  41. I've been using Laundry detergent on my roof to rid the roof of moss…simply spread the detergent on the roof on a dry roof & let the weather do the rest…once last for a few years!

  45. I have no reason to watch this video other than listening to Tommy’s New England accent. Number one preventive step for a homesick Rhode Islander.

  47. I use a pillow lol . Im not nailing or screwing into the roof of a million dollar home for a repair . An install i will..
    Cougar Paws and a pillow.

  48. Bleach does not kill plants I've poured pure bleach on weeds and grass in the cracks of my driveway and it did nothing and that was purely without being diluted

  52. The home owners plants are up on the siding and he has to spray the house to water them. That's going to cause so serious damage long term to the siding. 🙁

  58. My brother just moved (in January) to the Eugene, OR, area. He said that many roofs there (at least, in his neighborhood) have moss growing on them.

  59. I installed a zinc strip on my brand new shingle roof 3 years ago, moss is now starting to grow again and I live in vancouver, washington where it rains a lot so i will go back up and spray bleach on it again however i will use a stronger mix than you mentioned.

  63. So what happens when you need to go up on the roof again, which most do at times. You have to keep making all those holes in the roof to support the bracket or can you keep using the same holes you made and keep filling in with roof cement? I would think re-opening the holes all the time would weaken the shingle. Any comment on this. thanks.

  70. I'd give anything to have Tommy "the legend" Silva come to my home and help me with a project. I'd even film it for posterity sake. These guys are the GOAT of HI. Grew up watching them and I always will – in reruns!

  72. such as all wooden houses from the states , they are not going to last long, also I can see that the roof is not made for lasting more then a couple of years , so maintenance is very important here, I like very well the expert who is explaining how to fix everything , the way he explain is is really great , nice to see that he is a real expert .

  81. BEWARN! I took the Fall and Protection certification for my work, there are many safety protocol is not listed here: The weight of the individual to use the proper body harness, how the harness attach to the lower body which is VERY important! Any fall with even short distance needing to see emergency asap as it is no joke, people die when they thought it is no issue with a short distance fall. The improper harness will cause shock to the body and to the heart! The more you know the height safety, the more you learn not to mess with it unless you have taken the course of safety!

  82. Zinc doesn’t work except for the immediate area just below the inc strip. Moss will continue to grow. No offense to This old house. Still a good show.

  86. Laundry powdered detergent works great .Apply with a couple sunny days in the forecast . I would never put holes in the roof even after using silicone

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