Reuben's Home Inspection Blog

Zinc Strips Prevent Moss Growth on Roofs

November 3rd, 2011 | 19 comments

While black stains on roofs are a cosmetic issue, moss growth is more than just cosmetic.  Not only does moss look terrible on roofs, it will also shorten the life of the roof covering and possibly lead to roof leaks.  Whether you have wood or asphalt shingles, moss can grow on the roof if it doesn’t dry properly.

As with black algae stains, the most common place for moss to grow is on the north side of the roof, but if there are enough overhanging trees or other forms of shade, moss can really grow anywhere.  If you want to kill the moss, follow the link above that explains how to remove black roof stains; the process is the same for killing moss.  The results certainly won’t be as immediate, but it’s effective.  Today, the focus is on what you can do to prevent moss growth on your roof.

Have you ever noticed that moss and black stains don’t appear on roofs underneath the areas with galvanized metal?

Zinc washing off roof vents

The roof stays minty fresh zincy fresh below the vents because every time it rains, a small bit of zinc gets washed off the metal, which runs down the roof and kills whatever is growing on the shingles – whether it’s moss, algae, lichens… whatever.  If this is so effective, doesn’t it stand to reason that you could install strips of zinc along the top of the roof, and have them protect everything?  Of course.  You can actually buy rolls of zinc made just for this purpose.  The 50′ roll of zinc pictured below was about $25 at Home Depot.

Zinc Roll

The zinc is supposed to be installed at the ridges of the roof, or along the hips as needed to make sure that the rainwater washes zinc down the roof.

Zinc Strips Installed

Zinc Strips Installed

I’ve heard many roofers say that these zinc strips are worthless and ineffective, so I decided to conduct my own semi-long term test.  For my experiment, I installed a zinc strip along the ridge of a moss-covered garage roof approximately sixteen months ago.  I didn’t do anything else to this roof – no scrubbing, no chemicals, no nothing.  The before and after photos are shown below, and I think the results are pretty conclusive – zinc strips are effective at killing moss.

Mossy roof before

Before

Mossy roof after

After

That’s a pretty dramatic difference, isn’t it?  I cleaned up the roof a bit before taking the second photo by using a leaf blower, but that was all.  Remember, I applied that zinc strip to a roof covered in moss just to see what would happen; zinc strips aren’t supposed to be used as a moss remover, they’re supposed to be used as a moss preventer.  If you’re not in any hurry, they’ll apparently remove moss too though.

As they say, individual results may vary.  Zinc strips might not work for every application, but they’re not terribly expensive, and they’re not difficult for a roofer to install.  If you have an existing roof with a moss problem, try zinc strips.  Copper strips are supposed to work the same way.

Zinc strips are also supposed to be effective at preventing black stains from showing up on the roof.  I’m starting a long-term experiment on my own house; I’ll report back with the results in a few years.

Stay tuned ;-)

Reuben Saltzman, Structure Tech Home Inspections - EmailMinnesota Home Inspections

        

19 responses to “Zinc Strips Prevent Moss Growth on Roofs”

  1. Bill Thomford
    November 9, 2011, 5:39 am

    Where have you been Reuben? Must have been on Mars because this idea has been around for a long time.

  2. Reuben Saltzman
    November 9, 2011, 6:17 am

    Bill – I’m not saying this is a new idea.

    “I’ve heard many roofers say that these zinc strips are worthless and ineffective, so I decided to conduct my own semi-long term test.”

  3. George
    August 24, 2012, 9:41 am

    Option A: To get the results you are showing in that picture you had to wait sixteen months, purchase the zinc strips, and get on the roof with a leafblower? There is still moss on the roof?

    Option B: Hire a roof cleaning specialist and have a roof that looks brand new in less than a day?

    The ladder in the picture isn’t 3 rungs above the roof. It is an osha rule, for safety. Don’t risk your life goiing on a roof. Hire someone who does it for a living every day.

  4. Reuben Saltzman
    August 25, 2012, 5:55 am

    George – I think you missed the point of this post.

    “Today, the focus is on what you can do to prevent moss growth on your roof.”

    Sure, hiring a roof cleaning specialist to clean your roof will leave you with a clean roof, but this post was about the effectiveness of zinc strips when used to prevent moss growth.

    Also, why bring up OSHA rules when it has nothing to do with a homeowner?

  5. Haywood
    August 25, 2012, 10:56 am

    George is your typical internet troll who love to flame on posts, half cocked while posting from his mom’s basement.

  6. billy
    August 28, 2012, 7:14 pm

    Ha, thanks Reuben for a great example on zinc strips added without cleaning first , no one could give me a straight answer. Settle down George , OSHA. Doesn’t inspect homeowner projects, neither do they inspect your power washing business.

  7. BREN
    September 17, 2012, 5:23 pm

    I have a roof in Maryland that is an extreme case of shade and humidity. part of it has zinc strips installed 15 years ago. where they are is perfectly clean. where they are not is a jungle of mold, moss, and lichens. just had two new roofs put on with zinc strips even though every single roofer told me they weren’t necessary. i would never do another roof without them. the cost of zinc for a $10,000 roof is $75. evidently roofers don’t like them because the roof lasts too long or because they rip people off cleaning roofs. there is even one site that claims that they corrode and end up hanging down from where they were installed and other such b.s.
    i have learned so much in having three roofs put on that i am now consulting for people who need roofs and helping them cut through the b.s.. I guaranty that i will save them more than i charge. my no. is 410 224 4877.

  8. Thomas Delvecchio
    October 22, 2012, 4:59 pm

    Good Post.

    I have heard as well, that zinc strips do not work for moss control, so I created a post effectively countering that argument. The post below and the picture attached to it, show that zinc strips and any metal in general will stop moss growth. Thank you for taking your time in writing this,

    http://seattleroofcleaners.com/2012/06/26/seattle-roof-moss-removal/

  9. Greg
    February 5, 2013, 1:09 am

    Thanks for the info, Reuben! I just spent around 2 hours scrubbing 2 of the north facing areas of my roof in Oregon. I’ve been using Tide w/bleach to kill the moss, then a Nylon brush to knock it off, once it’s dead.
    Do I need to be roofer to install zinc strips? It does not look too technical.

  10. Reuben Saltzman
    February 5, 2013, 4:58 am

    Hi Greg, no, you don’t need to be a roofer to install those zinc strips. You just need to be qualified to work on roofs.

  11. janet robinson
    April 12, 2013, 9:13 am

    have read all the input to black on roofs,,,what would you recommend , 2″ or more of zinc strips….??? and what do you think this will cost to put on? or time to install on a total of 240′, ballpark figure…..it looks simple, but i am to old to climb anymore…i don’t want to be ripped off again, please give me some answers.. thanks, janet robinson

  12. Reuben Saltzman
    April 12, 2013, 3:32 pm

    Hi Janet, I’m guessing it would be about $500.

  13. michael
    April 23, 2013, 10:48 am

    Hi Reuben,

    I just read on another roofing site – where they confirm that zinc strips do work, but it needs to be installed every 3 feet from the roof peak to about 3 feet above the gutter. If I interpret this correctly, the roof will have horizontal stripes down the roof. Is this overkill? Are they making it worse than it really is – hence marketing for their services? Is one strip along the crest of the roof, like you described, sufficient? Thanks for the article and feedback. I live in Seattle and moss is our second state plant!

  14. Reuben Saltzman
    April 23, 2013, 1:59 pm

    Hi Michael,

    I’ve heard that moss is pretty much uncontrollable in Seattle. A good home inspector in Seattle actually sent me a photo of moss growing *on* the zinc strip. I think all bets are off for your area. http://buellinspections.com/some-roofs-have-moss-other-roofs-have-moss/

    - Reuben

  15. tommyb
    June 14, 2013, 3:36 pm

    I am a small hands on remodeler since latter ’70′s. The zinc strip works just like Mr. Saltz said, in Richmond Va- it “dries up” the lichens, mold, etc over time and the roof can be blown, swept clean. I have added this to so many roofs existing when I was doing other remodeling work. I highly recommend on new roofs since the mold no-stain warranties are not effective warranties as to the fine print.

  16. Ugly Shingles
    October 25, 2013, 7:36 am

    Zinc strips might help at first but once the strips patina the mold, moss, algae and lichen prevails and overtakes the zinc. I have a lot of pictures with all forms of bacteria growing on and around zinc strips.

    https://plus.google.com/100178692508580808627/posts/RUoxASPJ2Rv

  17. Bob
    October 27, 2013, 1:12 pm

    How do you remove the patina – so the zinc will continue to work?

  18. Reuben Saltzman
    October 28, 2013, 3:38 am

    @Bob – I’ve never tried.

  19. Brad
    November 1, 2013, 10:15 pm

    I have seen roofs where zinc is very effective, and I’ve seen roofs where it’s not as effective. I think that the correct approach is to analyze why this might be, as opposed to summarily dismissing their efficacy. To me, there are numerous factors that may limit/augment their effectiveness. Let’s identify some of them – 1. Light exposure – degree and duration 2. Wind exposure 3. Pitch of roof 4. Rainfall 6. Humidity/Aridity 5. Average temperature 5. Type of moss, algae that is colonizing 6. Proper/improper roof ventilation/insulation 7. Type of vapor retarder between shingles and roof deck. 8. Material used for roof deck, etc. The list could go on, but you get the gist. When analyzing any problem, you have to utilize a holistic approach; garbage in, garbage out. Personally, I think that the roof pitch has a lot to do with the decline in efficacy the further from the roof ridge that you get. I’ve seen steep roofs, with northern exposures, and pretty dense tree cover with zinc strips that looked great. Similar exposures with half the pitch didn’t fare as well, at least in my experience. For what it’s worth, I advocate their use but caution people to consider other factors that may help to mitigate the problem as well. Think outside the box!

RSS feed for comments on this post.

Comments on posts over 90 days old are disabled, as of 1/7/14.