Chuck Kramer’s home in Enumclaw, Washington, was built in the 1980s with unvented cathedral ceilings, insulated with cut-and-cobble rigid foam insulation and roofed with cedar shakes. A small section of the roof is showing signs of water damage, and now Kramer is trying to find a way of repairing the problem area without tearing into the rest of the roof.
As Kramer explains in a Q&A post at Green Building Advisor, the trouble seems to be in an area measuring about 150 square feet. This part of the roof, with a slope of 4-in-12, is surrounded by two other roof areas with a 12-in-12 pitch.
From inside to outside, the roof assembly consists of 2×6 tongue-and-groove boards, 15-pound asphalt felt, 2×6 rafters, 1×4 skip sheathing, and cedar shakes interwoven with strips of 15-pound asphalt felt. The rafter cavities are insulated with two 2-inch-thick layers of foil-faced polyisocyanurate foam insulation and 1 inch of Styrofoam beadboard.
“Most of the roof is 12/12 pitch,” he writes. “A small section above two bathrooms is 4/12, with two 12/12 pitches joining two sides with valleys. In that section, a skylight was cut in after initial construction, maybe in the late ’80s… The 1x4s [the skip sheathing] and a small part of the tops of the rafters are damaged by rot, particularly badly around the skylight.”
Kramer doesn’t see how he can increase the thickness of the low-slope portion of the roof without affecting the steeper parts of the roof. His proposed fix is to pull off the 1×4 skip sheathing, add a 1/2-inch layer of OSB with a peel-and-stick membrane, then a layer of 30-pound felt, and metal roofing. The 5,000 square feet of 12-in-12 roofing will not be affected.
Inside, he’s improved the bathroom fan capacity and covered the tongue-and-groove ceiling with drywall.
“In the long run,…