Do zinc strips work? Are they worth it?

The best evidence for strips in Greater Victoria is visual: on a 1960s Gordon Head or Lake Hill rancher with a long single north slope, the band below a ridge strip stays clean while the eave line greens up, and the line between the two is sharp. That is the 15-foot zone at work. On the steep, cut-up roofs of Rockland and Fernwood the same strip protects a dormer slope and nothing else, because rain never crosses from one plane to the next, and the owner concludes strips do not work. Both are right about their own roofs.

Local roofers are split on them, and the reluctance a homeowner meets is usually practical: lifting ridge caps on a 15-year-old roof can crack them, exposed-fastener strips can leak if badly sealed, and on a complex roof the crew would need six runs to do what one run does on a rancher. A contractor who declines is often saying the roof is the wrong shape for it, or that it is close enough to replacement that the money belongs in the new roof, where strips or an algae-resistant shingle can be built in for almost nothing.

Rain running over the metal dissolves a trace of zinc or copper ions and carries them down the slope; moss and algae are sensitive to those ions and new spores fail to establish in the zone the runoff covers. The effect fades with distance, which is the 15-foot figure, and with time as the metal weathers, faster for zinc than copper. It does nothing above the strip, nothing on a slope rain does not cross, and nothing to a mat that is already rooted in the granules. Remove first, then install; extension guidance from Oregon State says exactly that.

Zinc is cheaper and effective for several years before it weathers dull and loses potency; copper costs more, weathers to brown then green, and a 2026 Victoria guide describes it as active for 20 years or more. On a heavily shaded roof with a long life ahead copper is the better spend; on a moderately shaded roof with ten years left, zinc is fine. Either can be added at a re-roof under the ridge cap for material cost only, which is by far the cheapest way to get them.

• Zinc: lower cost, shorter active life
• Copper: higher cost, 20+ years, matches copper gutters
• Both: remove moss first, one run per 15 ft of slope
• Both: cheapest when added during a re-roof

Strips reduce how often you treat; they do not end it. A 2026 Victoria guide still recommends treatment every 12 to 18 months on high-risk roofs with or without strips, and the lower half of a long slope, the shaded side of a dormer and every valley remain vulnerable. Tree trimming does more than any strip. If a roof is green on the lower eave a year after a clean and a strip, the strip is working exactly as designed, and the answer is a second run midway down or accepting the shorter interval.