Don’t Zinc Strip

Zinc Strip Moss Control on roofs

Zinc Strips kill moss. The moss dies and the roof stays moss free for 10 feet under a zinc strip for five years or so if it stays in place and stays flat. Homeowners can install strips of zinc, purchased at a hardware store. Many people seek zinc strips because they have been well marketed and often recommended.  But let’s look at some disadvantages, then we’ll explain the very real principles by which they work. We’ll also explain the modern alternative.

1. Zinc Strip Installation Goes Against the Principles of Good Roofing
2. Strips of Zinc Oxidize and Loose Effectiveness
3. The Zinc Warps, Causing Uneven Treatment of the Roof
4. The Soft Metal Cracks and Breaks
5. A Lot of 50 foot Rolls of Zinc Strip are Needed
6. Installing Zinc Strips Requires Significant Safety Equipment
7. Environmental Problems
8. How Zinc Strips Work
9. Practical Experience
10. What To Do?

1. Zinc Strip Installation Goes Against the Principles of Good Roofing

If the zinc has been installed after roofing, the nails are exposed.  This is against good roofing principles, but it works for a while, because the nail head dints in the soft metal.  The truth that inevitably wins out in all exposed nail head situations is that expansion and contraction – a huge consideration in all roofing – works the nails out.  The nail hole gets looser and looser around the nail as this happens, and rainwater inevitably seeps in.  That’s erosion, and the beginning of the end of a roof’s viability.

2. Strips of Zinc Oxidize and Loose Effectiveness

When minor rust begins on the exposed zinc, it forms a new chemical composition on the surface.  The longer the rust grows, the less effective the zinc will be.

(Photo 2014 Asphalt Oxidizing)

3. The Zinc Warps, Causing Uneven Treatment of the Roof.

Within a year or two, the flat zinc material cups irregularly.  After all the effort of installation, we see that the water isn’t flowing over the strip evenly.  It’s rolling along the strip until it finds the least cupped points and then there is a good coverage of zinc particles only under the least cupped points. The warps and curls are creating uneven flow, as water runs along the strip to find the lower points. This is streaky coverage The uneven flow of metal saturated water creates uneven effectiveness which is clearly visible.

(Photo 2014 Cedar Ineffective)  (Photo 2014 Asphalt Ineffective)

4. The Soft Metal Cracks and Breaks.

Within five years, the thin zinc strips weaken and break at irregular places.  The material flops around the roof, looking bad and also hitting the surface of the roofing, causing a tiny amount of damage with each hit.

5. A Lot of 50 foot Rolls of Zinc Strip are Needed.

Properly, all angular caps must have zinc strip installed under them.  Running down each field of roof, there should also be a new horizontal line every 10-12 feet.  In the diagram, you see the zebra effect this gives to a roof.  The strips shine in the sun, so that’s not pleasing to the eye.  It’s not just an eyesore though, as you see in the other points we’re presenting here.

(diagram – Zinc Strip Install)

6. Installing Zinc Strips Requires Significant Safety Equipment

Today’s beautiful home designs often have complex architecture, and this is very evident in the roof structure.  Steepness is common.  Hips and valleys, dormers, etc. make a pleasing appearance, but create many hazards.  Worksafe BC has a lot to say about safety on roofs.  Heights over 10 feet require full safety gear, with certified anchors, ropes, rope grabs, lanyards and body harnesses.  Many homeowners have been seriously injured or killed simply doing things like cleaning gutters and installing Christmas lights.  Safety is a serious consideration when considering roof care and maintenance.

7. Environmental Problems

Zinc is a pollutant that, in enough quantity, kills fish.  Copper and other metals are also harmful in this way.

8. How zinc strips work

Since simple plant life forms are the main culprit in deterioration, their reduction is the logical approach to preservation.  Metals like zinc, copper, and some kinds of galvanized steel are poisonous to simple plant life.  On a sloped roof, these can be used to control moss.  The idea is to place them near the top of the field of roof on which you want to control the moss.  Rain water runs over the metal and down the roof field.  As it rolls over the metal, the water picks up molecules of metal, and carries them down the roof.  The wetness triggers the moss to feed and drink, but the metals damage the moss.  This happens repeatedly until the moss is killed.  Moss won’t start in this environment, so this is very effective as far as it goes.

9. Practical experience

Those of us who have worked on roofs and observed them carefully agree that zinc strips are detrimental to long term roof health.  That’s too bad, because zinc strips are supposed to help roof health.  But here is what we run into, day by day, in roof maintenance.  The strips are rarely placed close enough together.  Since they only work for ten feet downward or so, they should be placed regularly down the field, horizontally.

So, roof maintenance people are often removing cupped, warped, broken zinc strips and repairing the nail holes.  We do not like zinc strips.

10. What to do?

ROTban – Cleaning Treatment That Lasts – has been developed through years of research testing to be a method of moss control that doesn’t use metals or other fish harming substances.  As a method that doesn’t require nailing and that isn’t visible to the eye, except for the cleaning effect it has.  Without using nails or building products to fail and cause problems later, it’s safer.  It’s applied in such a way as to bond into the cells of the roofing material, and stay bonded, activating with each rainfall and working on the spot and for a distance below the spot. The result is continuous, completely even performance throughout the roof field, and thus a beautiful appearance.  By creating an environment on the building material that will not allow microbes to feed there, working with each rainfall in a way similar to the zinc strip concept, it passes every test that zinc strips fail.  Everywhere it is applied, which should be on the entire roof, it’s working with each rainfall. When applied by trained technicians, it is the answer to the problem of moss on roofs.

So use of zinc strip has limited value. On the other hand, ROTban has great value and economy.