Untreated and preservative-treated western woods as roof shingles: 10th year appraisal

Miller, D.J.

Untreated and preservative-treated western woods as roof shingles: 10th year appraisal

1991

Miller, D.J.

Untreated and preservative-treated shingles of western redcedar, sugar pine, western hemlock, and western larch were exposed to two environments--one intermediately favorable to, and one highly favorable to decay of wood above ground. Under the intermediate conditions, untreated shingles of western hemlock and sugar pine seriously decayed in 10 years. Much less decay developed on western larch, and little or none on western redcedar. Treatments consisting of brushing shingles in position or dipping them in solutions of chromated copper arsenate type B (CCA-B, 9% a.i.) or pentachlorophenol (penta; 5% a.i.) provided good protection except on sugar pine with sapwood that was not accessible to brushed-on treatment with penta. Under more severe conditions, untreated shingles of western redcedar remained essentially sound for 9 years, but the other untreated shingles were seriously decayed or destroyed. Preservative treatment greatly reduced the occurrence of decay, except in penta-treated sugar pine and CCA-B-treated hemlock. Surface decay was usually most severe beneath the butt of overlapping shingles, but decay rarely developed on faces exposed to the weather, regardless of whether they were treated or not. Checks and splits in treated shingles were usually not associated with decay pockets. It should be noted that environmental concerns now preclude use of penta and CCA-B on roofs; these preservatives have been replaced by safer ones.

اظهر المزيد [+]