How to Install Zinc Strips to Slow Moss Growth on a Shingle Roof
Zinc slows regrowth below the strip. It does not clean moss that is already there, and it does not work everywhere on a roof.
- Advanced
- 2 to 5 hours
- Updated
The short answer
Zinc strips are narrow metal strips installed under the ridge cap or a shingle course near the top of a roof slope. Rain washes trace zinc ions down the roof, which slows moss and algae growth on the shingles below. They do not remove existing moss, so clean the roof first. Expect protection for only a limited distance below each strip, and confirm the spacing with the manufacturer.
Moss is the most common complaint on Fraser Valley roofs. Long wet winters, shade from cedars and firs, and needles and debris that hold moisture create ideal conditions for moss and algae on the north and shaded slopes. Moss lifts shingle edges, holds water against the surface and shortens roof life. If you want to see what causes it and how to handle it, read the moss and algae removal guide.
Zinc strips are a preventive measure. When rain hits the zinc, a small amount of zinc dissolves and runs down the shingles, where it makes the surface hostile to moss and algae. The effect is gradual, and it only works on the area the water reaches. Zinc does not clean moss that is already growing. Existing moss must be removed first, and roofs should never be pressure washed, since that strips the granules from the shingles and shortens their life.
This guide covers how the strips are installed on asphalt shingle roofs and sets realistic expectations. They help, especially combined with clearing debris from the roof, but they are not a cure on a roof that stays in deep shade.
Tools
- Roofing hammer
- Tin snips
- Flat bar
- Caulking gun
- Tape measure
- Extension ladder with stabilizer
- Roofing harness, rope and anchor
Materials
- Zinc strips, commonly about 2 to 3 inches wide and 50 feet per roll or in short lengths
- Galvanized or zinc-compatible roofing nails
- Asphalt roofing cement or sealant for nail heads
- Pieces of matching shingle where needed
Safety first
- Moss and algae make a roof extremely slippery, even in dry weather. Do not walk a mossy roof without fall protection, and clean or treat the moss from a safe position first.
- WorkSafeBC requires fall protection where a fall could be 3 metres (about 10 feet) or more, and this work is on the upper part of the slope near the ridge.
- Zinc strips are sharp at the cut edges. Wear gloves, and keep cut scraps out of the gutter and lawn.
Step by Step
Step 1: Clean the moss off first
Zinc slows regrowth and does not kill established moss. Brush dead moss off gently from the top down with a soft brush, or use a treatment made for roofs, following its label. Avoid pressure washing, which blasts granules off the shingles and opens them to UV and water.
Clear needles and debris too. They hold water against the roof and feed moss, see how to clean debris off a roof.
Watch out: Do this work from a safe position. A mossy roof is as slippery as ice.
Step 2: Decide where the strips go
Zinc protects only a limited distance below the strip, commonly a few feet, because the ions dilute as they run down. Short slopes can be protected from a strip at the top. Longer slopes need another row partway down, spaced as the manufacturer recommends. Check the product instructions for the distance.
Shaded slopes, such as the north side under trees, benefit most. Also plan around vents and skylights, which split the flow of water.
Step 3: Choose strips and check metal compatibility
Zinc is often used on roofs with aluminum or steel flashings and gutters without problems, but runoff from copper can harm the shingles and corrode other metals. Do not mix copper and zinc on the same roof section unless the manufacturer says it is fine. Follow the instructions for the product.
Step 4: Lift the shingle course at the installation line
Near the ridge, you can install the strip under the ridge cap, with about 1 inch of zinc showing below the cap's edge. For strips lower on the roof, choose a line in the shingle courses and lift the course above to slide the strip in.
Work in mild, dry weather. Cold shingles crack and the hand sealing later will not bond. Lift only as much as needed.
Step 5: Slide the strip in and set the exposure
The strip has to be exposed to rain, or it does nothing. About 1 inch showing is the usual guide, but follow the manufacturer's instructions. Run the strip the full width of the roof plane, lapping lengths by a couple of inches. Cut with tin snips, and bend the last inch over if needed.
Step 6: Fasten the strip at the top edge only
Fasten along the upper edge of the strip, where the course above covers the heads. Nails through the exposed part create leak paths. Use galvanized roofing nails, placed about every 12 to 16 inches, or as the product instructions say.
If any nail head ends up exposed, cover it with a small dab of roofing sealant.
Step 7: Reseal the shingles you lifted
The seal you broke will not reactivate immediately. Follow the technique in how to reseal lifted or unsealed shingles. Check that the strip does not stop shingles from lying flat.
Step 8: Keep up with debris and check each year
Zinc works on a clean roof. Needles and leaves that hold moisture create moss in the spaces the water does not wash. Expect the zinc to lose its bright finish and oxidize to a dull grey. That is normal, and it still works. Replace strips that have corroded away or shifted.
What to Expect in the Fraser Valley
In wet, shaded conditions, zinc can slow moss noticeably on the area below the strip, but it is not a guarantee. Slopes under cedars and firs that are never reached by sun, or roofs with heavy needle accumulation, will still grow moss in the gaps that zinc runoff does not reach. Trim overhanging branches to get sun and air to the roof, which works alongside the zinc.
Zinc Strips or Treated Shingles
Some shingles are made with algae-resistant granules, and they help against the black streaks that algae cause, but less against moss. Zinc strips can be added to any roof, old or new. On a roof near the end of its life, it is usually better to put money toward replacement than toward strips.
Common Mistakes
- Expecting strips to clean existing moss. They only slow regrowth below them. Remove the moss first.
- Pressure washing first. It strips shingle granules and shortens the roof's life.
- Strips too far apart. The zinc effect fades with distance. Follow the manufacturer's spacing on long slopes.
- Covering the exposed edge. If the strip is buried under shingles, rain does not run over it and it does nothing.
- Nailing through the exposed part. It creates leak points. Nail only at the top edge under the course above.
- Using zinc with copper. It can cause corrosion and staining. Keep them separate.
When to Call a Professional
Call a roofer for any installation on a steep or high roof, on a roof that is already heavily covered with moss, or where shingles are brittle and crack when lifted. Moss that has lifted shingles or rotted the edges needs more than zinc, and sometimes replacement.
A roofer can also assess whether a roof is worth protecting. If the shingles are close to the end of their life, strips will not add much.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Emergency Roof Repair service or the towns we cover.
How to Install Zinc Strips to Prevent Moss: Questions
Do zinc strips really work to prevent moss on roofs?
They slow moss and algae growth on the shingles below the strip, because rain washes small amounts of zinc down the roof. They work best on a clean roof and on short slopes, and less on heavily shaded areas or under debris. They do not remove moss that already exists, so clean the roof first.
How far down the roof do zinc strips protect?
It varies by product and conditions, but protection is limited to a few feet below each strip, because the zinc dilutes as it runs down. Long slopes usually need a second row partway down. Confirm the spacing with the manufacturer's instructions for the strip you are using.
Can I install zinc strips myself?
It is possible, but the work is near the top of the roof slope where falls are most dangerous, and the roof is often mossy and slippery. You also need to lift shingles without cracking them and reseal them. On anything steep or high, a roofer with proper fall protection is the safer way.
Should I pressure wash moss off my roof?
No. Pressure washing strips the protective granules off asphalt shingles, which shortens their life and can void warranties, and it can force water under the shingles. Remove moss with a soft brush or a treatment made for roofs, used according to its label, and then use zinc strips to slow regrowth.
How long do zinc strips last?
Zinc is a long-lasting metal, and strips commonly keep working for many years, but they gradually dissolve as they release zinc, and they may need replacing when thin. They turn dull grey as they weather, which is normal. The life depends on rainfall and strip thickness, so check the product information.
Related Guides
All Roof Repair guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
Want someone to look at your roof?
Kory & Johnny have roofed homes across the Fraser Valley since 2016. Free inspections, honest estimates, no pressure.
604-728-0146Text UsEmailServing Hope, Agassiz, Chilliwack, Rosedale, Abbotsford & the entire Fraser Valley