If you own a home in Beaverton, Hillsboro, Tigard, or anywhere on the west side of the Portland metro, moss on the roof is likely a recurring issue. The combination of wet winters, mild temperatures, and significant tree canopy in established neighborhoods creates ideal conditions for moss to establish and spread on asphalt shingles.
Zinc strips are one of the options homeowners encounter when looking for ways to slow or prevent moss growth. This post explains how zinc strips work, what they can and cannot do, and how they fit into a broader approach to moss control on west side roofs.
Why the West Side of Portland Has a Persistent Moss Problem
Beaverton sits in the Tualatin Valley in Washington County, on the west side of the Portland metro. According to Best Places climate data, Beaverton averages around 41 inches of rain per year and approximately 155 days of precipitation annually. Only 141 days per year are considered sunny, compared to a US average of 205.
Those numbers reflect a climate where roofing materials spend a significant portion of the year wet, particularly from October through April. West side neighborhoods in Beaverton, Hillsboro, Tigard, Aloha, and Sherwood share similar conditions. Homes under heavy tree canopy from Douglas firs and big-leaf maples lose additional drying time because the canopy blocks what limited winter sunlight is available.
The result is roofing surfaces that stay consistently damp for months at a time, which is exactly the environment moss needs to establish and spread. North and east-facing slopes are most affected because they receive the least direct sun even on clear days.
For more on why organic growth is such a consistent issue in this part of Oregon and what the different types of growth do to a roof, see our post on moss, mold, and algae on Portland roofs.
What Zinc Strips Are and How They Work
Zinc strips are thin metal strips installed along the ridgeline of a roof and sometimes at intervals down the roof slope. When rain falls on the roof, it flows over the zinc strips and picks up zinc ions. That zinc-infused water then runs down the slope, creating an environment where moss, algae, and other organic growth have difficulty establishing.
The mechanism is straightforward. Zinc is toxic to simple plant life including moss, algae, lichen, and mold. As rainwater carries zinc ions across the shingle surface below the strip, it inhibits those organisms from forming colonies. According to GAF’s installation instructions for zinc moss prevention strips, the strips are installed along both sides of the ridge with most of the strip left exposed to rainfall.
One important constraint: zinc strips only protect the area of the roof directly below them. According to installation guidance from multiple manufacturers and roofing sources, the effective range is roughly 10 to 15 feet downslope from the strip. On a longer roof slope, a single ridgeline installation does not protect the entire surface. Additional strips installed at intervals down the slope are needed for full coverage.
What Zinc Strips Can and Cannot Do
Understanding the realistic limits of zinc strips helps homeowners set accurate expectations before committing to them as a solution.
What they can do. When installed correctly on a clean roof with no existing moss growth, zinc strips can meaningfully slow the rate at which moss and algae re-establish. They work continuously as long as rain is flowing over them, which in Beaverton’s climate means they are active for most of the wet season. For homeowners who have had a roof cleaned and treated and want to extend the time before the next cleaning is needed, zinc strips are a reasonable addition.
What they cannot do. Zinc strips do not kill or remove existing moss. They are a preventive measure, not a treatment. Installing zinc strips on a roof that already has active moss growth does not address the existing colonies. The existing growth needs to be treated and cleared first.
Zinc strips also lose effectiveness over time. Studies cited by roofing sources suggest zinc strips can provide meaningful protection for approximately five years before their output declines enough to require replacement or supplementation. They are not a permanent solution.
Coverage limitations on larger roofs. A single ridge installation on a roof with a long slope provides incomplete protection. The lower portion of the slope receives little to no zinc runoff from a ridgeline strip alone. On homes in Beaverton’s established neighborhoods where tree canopy shades the lower portions of the roof most heavily, that gap in coverage is exactly where moss tends to be most aggressive.
Installation carries risk on existing roofs. This is worth knowing before pursuing zinc strip installation on an existing roof. The Asphalt Roofing Manufacturers Association has noted that installing zinc strips on an existing roof is a leak liability. Doing so requires either nailing directly through shingles or lifting shingle edges to slide the strip underneath, both of which compromise the seal of the roofing system. On an aging roof, this risk is amplified. A qualified contractor should assess whether the current condition of the roof makes zinc strip installation advisable.
Zinc vs. Copper Strips
Copper strips work on the same principle as zinc, releasing ions into rainwater that inhibit organic growth. The key differences are longevity and performance.
Copper is more durable than zinc. Where zinc strips typically maintain effectiveness for around five years, copper strips last significantly longer and are less prone to warping. Copper is also a more potent inhibitor of moss and algae at equivalent concentrations. The tradeoff is that copper strips are more visible and can cause discoloration on shingles over time as the copper runoff stains the surface below.
Both zinc and copper are preventive rather than corrective. Both require the roof surface to be clean before installation to be effective. And both have the same coverage limitation: they only protect the area below the strip.
The Role of Algae-Resistant Shingles
For Beaverton homeowners who are replacing a roof rather than treating an existing one, algae-resistant shingles are the most integrated form of moss and algae prevention available. Both Owens Corning and Malarkey Roofing Products offer shingles with copper-infused granules that inhibit algae growth across the entire shingle surface rather than just in the runoff path below a strip.
The copper is embedded in the granules themselves, so the protection extends across the full roof surface and does not rely on rainfall carrying ions from a single point. This approach does not eliminate moss in a climate as wet as Beaverton’s, but it meaningfully reduces the rate at which algae establishes and slows the conditions that lead to moss growth. For an overview of manufacturer options and what sets them apart in the Pacific Northwest climate, see our post on top roofing manufacturers for your home.
A Practical Moss Management Approach for West Side Homeowners
Zinc strips are one tool in a broader set of practices. In Beaverton’s climate, no single measure eliminates moss risk entirely. A combination of approaches is what makes a practical difference over time.
Keep gutters clean and flowing. Clogged gutters cause water to back up at the eave line, keeping the base of the roof saturated for extended periods. That persistent moisture at the lower edge is a consistent source of moss establishment on west side homes. Our gutter guide for Oregon homeowners covers cleaning frequency and what to look for. For guidance on when gutters themselves need replacing, see how long do gutters last.
Trim overhanging branches. Branches that overhang the roof deposit organic debris directly onto the shingle surface and block sunlight. Both create the conditions that accelerate moss growth. Keeping branches back from the roofline reduces debris accumulation and allows more drying between rain events.
Treat existing moss before it deepens. Moss caught early, before the rhizoids have anchored deeply into the shingle surface, can be treated with chemical solutions without lasting structural damage to the shingles. The longer it is left, the more damage occurs beneath the surface. Our post on Oregon winter roof damage explains how sustained moisture contact degrades roofing materials over a full wet season.
Consider zinc or copper strips on a clean roof. If you have had a professional treatment done and want to extend the interval before the next one is needed, zinc or copper strips installed correctly on a clean roof are a reasonable addition. Have a qualified contractor assess the condition of the roof before installation to confirm the shingles are in good enough condition to support it without risk of creating new leak points.
Consider metal roofing at replacement time. Metal roofing surfaces do not support the organic growth that asphalt shingles do. In Beaverton’s climate, where moss maintenance on composition shingles is a recurring and ongoing requirement, metal largely removes that concern for the life of the roof. For a full comparison, see our post on metal roof vs. asphalt shingles in Portland.
When Moss Growth Points to Replacement
Zinc strips and moss treatments are appropriate when the underlying roof system is structurally sound. When the roof has been significantly damaged by sustained moss growth, preventive measures address the surface without resolving what is underneath.
Signs that replacement is the more appropriate conversation include shingle edges that have been physically lifted across a significant area of the roof, widespread granule loss in areas where moss has been dense, a roof approaching or past the end of its expected service life, and interior signs of moisture intrusion such as ceiling stains or damp insulation in the attic.
For more on how to assess where a roof stands and when repair or replacement makes more sense than continued treatment, see our posts on roof repair vs. replacement in Portland and our full roof lifespan guide by material.
About Peak Performance Roofing
Peak Performance Roofing is a family-owned company serving Beaverton and the west side of the Portland metro, along with the broader surrounding area. We specialize in roof replacements and install composition, metal, and tile roofing systems. We are a preferred contractor with both Owens Corning and Malarkey Roofing Products and are recognized as a top 1% roofing contractor in Oregon.
We serve Beaverton, Hillsboro, Tigard, Sherwood, Tualatin, Lake Oswego, Wilsonville, Oregon City, and Portland.
You can read what past customers have said on our reviews page and find answers to common questions on our FAQ page.
Schedule Your Free Roofing Quote
If your west side home has moss growth and you are not sure what condition the roof underneath is in, or if you are due for a replacement and want to discuss material options that reduce ongoing maintenance, the next step is a free roofing quote from our team. We will walk through what we find, explain your options clearly, and give you a detailed quote with no pressure and no obligation.
Schedule your free roofing quote today or call us at 971-436-1738.
Peak Performance Roofing serves Beaverton, OR and the surrounding west side communities. CCB: 231484 | WA: PEAKPPR788NS
