How algae-resistant granules work
Asphalt shingles are surfaced with mineral granules. Algae-resistant shingles replace some of these with copper-coated granules. Rainwater picks up trace copper ions from the granules and carries them down the slope, inhibiting algae growth. The effect is similar to a zinc strip but distributed across the roof surface and built into the shingle from the factory.
Algae warranties by manufacturer
GAF StainGuard Plus (Timberline HDZ): 10-year algae warranty on listed colors. GAF StainGuard Plus PRO: 25-year algae warranty available with credentialed installer registration. OC StreakGuard (Duration): 10-year algae warranty. CertainTeed StreakFighter (Landmark): 10-year algae warranty. IKO AR coating: 10-year limited algae warranty. Malarkey 3M Scotchgard Protector: 30-year algae warranty (industry-leading). The warranty length is a useful proxy for the granule concentration; longer warranties indicate more copper-coated granules.
What algae-resistant shingles don't address
Heavy moss. Moss is a different organism than the cyanobacteria the copper granules target. Moss develops in wet, shaded conditions, holds moisture against the shingle surface, and can lift tabs over time. Algae-resistant granules slow the cosmetic black streaking but do not prevent moss growth. For Portland moss management, you need zinc strip preventive maintenance (which works by similar chemistry but applies more concentrated dosing across the roof surface) plus periodic soft-wash cleaning.
Should you pay extra for algae resistance?
On modern architectural shingles, algae resistance is typically included in the base price (it's a manufacturing standard, not an upgrade). The only situation where you'd be choosing between AR and non-AR is on lower-end product lines or 3-tab shingles. For any architectural install in 2026 Portland, AR-rated shingles should be the default. The extended algae warranty (GAF StainGuard Plus PRO, Malarkey 3M Scotchgard) typically requires a credentialed installer.
Color matters for visible algae streaking
Black streaking is most visible on light-colored shingles. Light-gray, Driftwood, or Heather Blend shingles show streaking earliest and most obviously. Charcoal, Onyx Black, and dark Slate colors hide minor streaking. If your roof is north-facing and likely to develop streaking, darker colors will look better longer between cleanings.