A roofing experiment: zinc strips on a roof

Reblogger Maureen McCabe
Real Estate Agent with HER Realtors

I love experiments.   Reuben Saltzman, a Minneapolis MN home inspector is doing "A semi-long term experiment: zinc strips on a moss covered roof"

Have you run into moss on your roof?  I would think it would be more common in MN and cooler northern states in the Great Lakes area  than in Ohio but I have seen it here on homes with a lot of tree cover.  We certainly get enough rain...    Visit home inspectors in the Pacific Northwest's websites if you want to see moss covered roofs.  

I remember moss on an Old Worthington roof, and I have seen moss on the northside of a ColOld Worthington sign with treesonial Hill's roof, so I guess moss happens in Worthington and other Central Ohio communities. 

We do have lots of ugly black algea stained roofs in Central Ohio, a cosmetic issue, according to Reuben.  Reuben's first photo of the black algae stains caught my eye.  I just noticed on a roof in Columbus that the area under metal vent caps did not have the algae stains.

Reuben did a wild and crazy experiment a few years back with ice.... using pantyhose on the roof / gutters.   I think Reuben had another roofing experiment where he ran wires along the gutters... I doubt I Re-Blogged that experiment... too scary, even with "Don't try this at home!" warning.  Thanks to Reuben for allowing this home maintenance experiment post to be Re-Blogged. 

Makes me wonder do roofers use zinc strips on roofs for the ugly black algae in our area?  

Original content by Reuben Saltzman

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


Mossy roof 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 couple years.

Stay tuned  ;-)


Reuben Saltzman, Structure Tech Home Inspections - Email - Minneapolis Home Inspector



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Gary L. Waters, Broker Owner, Waters Realty of Brevard, LLC
Waters Realty of Brevard, LLC - Melbourne, FL
... a small office, delivering big service!

This is an interesting post. I have never heard of the zinc use for algae. Amazing what you learn on AR!

Nov 08, 2011 02:40 PM #1
Maureen McCabe
HER Realtors - Columbus, OH
Columbus Ohio Real Estate

I never heard of it until Reuben's post. Great discussions on the original post with people from all over the country including home inspectors from the PNW... 

I asked someone from the roofing supply industry about whether zinc strips are used in our market.  He said newer shingles there can be zinc granules among the shingle granules.

Nov 08, 2011 02:51 PM #2
Christine Bohn
RE/MAX Professionals - Gainesville, FL
Realtor, Gainesville FL

Maureen - This is very cool. I love "science stuff", and that's just what this is.   We have those same stains here on roofs because of oak & pine canopy over homes.  I wonder why this isn't used more??   I just might have to ask one of my roofing contractors.  

Nov 08, 2011 07:59 PM #3
Maureen McCabe
HER Realtors - Columbus, OH
Columbus Ohio Real Estate

Thanks Christine Great discussion on his original post among the home inspectors.  It is so odd my real estate Paper.li (not necessarily real estate news)  picked you you Re-Blogging Reuben.  I had never heard of zinc strips before his post. 

Nov 09, 2011 08:33 AM #4
Rob Ernst
Certified Structure Inspector - Reno, NV
Reno, NV-775-342-4767- Inspector & Energy Auditor

I knew of the powers of zinc but I have never seen anyone do a before and after test like this. You should be able to sell it to the zinc manufacture for marketing.

Nov 17, 2011 10:06 PM #5
hi james if your still knoking around i think this is there web address and details,check out there great prices , mention myself-netsimsy told you to ring
Jul 24, 2012 03:14 PM #6
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Maureen McCabe

Columbus Ohio Real Estate

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