We installed 18" western red cedar "perfection" shingles by Watkins Mill treated with Chromated Copper Arsenate for longevity on this historical reproduction residence. The first step was installing continuous CertainTeed WinterGuard® ice and water shield across the roof decking followed by Benjamin Obdyke Cedar Breather matt to assure proper air circulation beneath the shingles. All valleys were flashed with 20 oz red copper.