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The cape-style post-and-beam house was five years old when I first saw it. The builder who had originally built the shell had opened up one wall to build an addition. What he found under the rigid foam insulation on the exterior was severe rot in the pine board sheathing. The pattern of rot closely followed the post-and-beam framing. The frame was built with 8x8 hemlock timbers, and the spaces between the timbers were filled in with 2x4 framing. The 2x4 infill walls were insulated with R-11 fiberglass and covered with 4-mil poly and drywall on the inside (see illustration). The exterior was sheathed with 1x8 diagonal pine boards, covered by 1 inch Styrofoam rigid insulation. The siding was backprimed pine clapboards. The