Western red cedar shingles, untreated and treated with three waterborne preservatives, have been exposed since 1980 at two locations in the lower mainland of British Columbia. An inspection performed after twenty years in test revealed some decay in untreated samples, while all treated samples with the exception of one CCA-C-treated and one ACA-treated shingle were free from decay. Moderate physical deterioration of the shingles had occurred in the form of erosion and splitting.