Case Study: Saanich Peninsula Cedar Shake Treatment — Restoring Historic Wood Roofing
Professional Treatment Protocol for Lichen and Moss on Wooden Shake Roofing
Quick Answer
A 1980s Saanich Peninsula waterfront property featured 1,800 sqft of cedar shake roofing with mixed north and south-facing exposure. The north-facing sections showed Stage 2 moss (25–50% coverage) with significant lichen colonization — white and orange lichen lichens typical of ocean-exposed cedar.
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A 1980s Saanich Peninsula waterfront property featured 1,800 sqft of cedar shake roofing with mixed north and south-facing exposure. The north-facing sections showed Stage 2 moss (25–50% coverage) with significant lichen colonization — white and orange lichen lichens typical of ocean-exposed cedar. Unlike asphalt treatment, cedar shakes require different biocide formulations and application protocols to avoid wood fiber damage. Professional cedar-specific treatment, applied in spring 2022, achieved moss control while preserving the wood's natural color and oil content.
Cedar Shake Specific Challenges: Porosity, Oil Content, and Lichen Complexity
Cedar shakes present three treatment challenges absent in asphalt roofing: (1) extreme porosity — cedar wood is open-grained, allowing deep biocide penetration into the wood itself; (2) oil content — cedar's natural oils are susceptible to degradation from harsh oxidizing biocides, potentially accelerating wood aging; (3) lichen complexity — lichen is a symbiotic organism (fungus + algae), requiring different kill mechanisms than moss or cyanobacteria alone. Standard 3–4% sodium hypochlorite (effective for asphalt) would damage cedar by oxidizing surface fibers and depleting natural oils. The Saanich property required cedar-specific biocide: 1.5–2% copper-based fungicide combined with a chelated zinc formulation. This formulation targets the algal partner of lichen (zinc is toxic to algae) and the fungal partner (copper is fungistatic). Additionally, the biocide was combined with a cedar-compatible oil treatment to restore depleted wood oils post-treatment.
Pre-Treatment Condition: Lichen Dominance with Secondary Moss
Initial assessment showed: 40% orange/red lichen (Xanthoria species, sun-loving), 30% white lichen (Physcia/Parmelia species, shade-tolerant), 20% green moss (Dicranum scoparium), 10% bare wood visible. The roof was oriented 30% south-facing (higher lichen relative to moss), 70% north-facing (higher moss relative to lichen). No visible wood rot was detected, but wood moisture content was elevated (22–25% vs. ideal 12–15% for cedar), indicating chronic moisture retention from biological growth.
Treatment Approach: Cedar-Specific Biocide Plus Oil Restoration
Treatment sequence: (1) low-pressure (500psi) initial rinse to remove loose lichen and moss debris without damaging wood fibers (unlike pressure washing which would damage cedar); (2) application of 1.8% copper fungicide + zinc chelate biocide with 40-minute dwell; (3) post-treatment low-pressure water removal to rinse residual biocide; (4) application of penetrating cedar oil treatment to restore depleted wood oils. Total timeline: 5 hours for the 1,800 sqft roof; cost $380 (approximately $0.21/sqft for biocide + oil treatment). The extended application time (vs. asphalt treatment) reflects the need for careful low-pressure work and the additional oil restoration step.
Post-Treatment Recovery: 6-Month and 18-Month Results
At 6 months post-treatment (fall 2022): Moss and lichen had turned gray-brown (dead pigmentation) and began shedding. Wood moisture content dropped to 18–19% (still elevated but improving). The cedar color remained warm amber-brown (the oil treatment maintained pigmentation vs. bleaching that would occur from standard hypochlorite). At 18 months (winter 2023): Approximately 85% of dead lichen and moss had naturally shed. Wood moisture content stabilized at 15–17% (within acceptable range). New lichen establishment was minimal (trace amount of Xanthoria on sun-exposed south-facing sections). No moss re-establishment on north-facing sections. The wood appearance was restored — light golden-brown cedar color without gray staining typical of untreated wood roofs.
Long-Term Preservation and Economic Value
Cedar shake roofs typically require replacement at 25–30 year lifespan if exposed to unchecked biological colonization (accelerated decay rates due to moisture retention and rhizoid penetration). The Saanich property's roof was installed in 1982 (38 years old at time of treatment). Without professional treatment, the roof would have been economically at end-of-life. With treatment, the roof lifespan is extended an estimated 5–8 years, avoiding replacement cost of $16,000–20,000. Treatment cost was $380 — representing 2% of replacement cost for 5–8 years of preserved function. The aesthetic improvement (restoration of wood color and patina) also increased property marketability and maintained architectural character of the waterfront cottage.
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Frequently Asked Questions
Why use different biocide for cedar than for asphalt?
Cedar is wood — a living material with natural oils and porosity. Standard hypochlorite oxidizes the wood fibers themselves, accelerating decay. Cedar-specific biocides (copper, zinc) target the biological organisms without damaging the wood structure.
How long does cedar oil treatment last?
Penetrating cedar oils last 12–18 months depending on UV exposure and rain intensity. Reapplication every 18–24 months maintains oil content and color.
Will the moss return faster on cedar than on asphalt?
Cedar shows faster biological re-establishment if untreated because the wood provides better nutrient substrate than asphalt. However, with professional treatment and oil maintenance, cedar can remain clean longer than untreated asphalt.
What's the difference between lichen and moss on roofs?
Lichen is a symbiotic organism (fungus + algae); moss is a multicellular plant. Lichen is more resistant to standard bleach treatment because the fungal partner is less susceptible to oxidative biocides. Both require treatment, but lichen requires copper/zinc formulations for optimal kill.
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About Roof Labs Canada
Roof Labs Canada is Vancouver Island's roof preservation and surface intelligence company — providing biocide treatment, biological growth elimination, and surface protection for asphalt and cedar roofing systems. As Roof Labs Canada — Cedar shake treatment specialists, we bring marine-engineered formulas, 9+ years of island experience, and a written 2-year guarantee to every project.
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