High Performing Buildings - Spring 2009 - (Page 54) Drainage Plane Continuity Draining water away from the enclosure starts at the roof. The rooftop vents were removed, and the roof was stripped down to the original board sheathing. Two layers of foil-faced foam were installed followed by a new layer of plywood sheathing. The roof sheathing was covered entirely with ice and water shield and new shingles were installed. Care was taken to retain the depth of the original overhang which was achieved by furring out the fascia board. The original wall shingles had been covered with aluminum siding. The siding was removed and hauled away by a scrap metal contractor. The shingles were removed to expose the original board sheathing. A corrugated house wrap was installed over the board sheathing and connected to the window wrap as well as the top and the bottom of the wall sheathing (with a continuous bead of caulk for air barrier continuity). Then, the two layers of 2-in. polyisocyanurate were applied with the joints staggered and taped with adhesive construction tape. The insulation board was held in place with 1 by 3 furring strips screwed back to the board sheathing. The pre-primed cedar siding was then attached to the furring strips. This resulted in a ¾-in. space (open at top and bottom) that allows drainage of water and ventilation to dry much of the remaining water. Multiple mechanisms in the new assembly shed water. When rain hits clapboard siding, the majority of the Wood furring strips hold exterior foil faced rigid insulation in place. The windows are recessed inboard of the rigid insulation so that interior window trim geometry was not altered. The interior look remained true to the original design. 54 HigH Performing Buildings spring 2009
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