Performance of Several Western Woods as Roof Shingles with and Without On-Site Preservative Treatments

Untreated and nonpressure-treated shingles of western redcedar, sugar pine, west coast hemlock, and western larch were exposed to outdoor conditions intermediately favorable to decay of wood above the ground. After 3 years, shingles retained 0.21 and 0.80 pcf of chromated copper arsenate near weathered surfaces, depending on species. Low retentions of penta (> 0.02 pcf) still retarded fungal growth. After 5 years, all treated shingles remained sound except for a few cedar shingles that were predisposed to rapid breakdown by collapsed springwood; a few untreated hemlock and pine shingles had begun to decay.

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