While contractor Tom Silva installs sidewall shingles on the Concord, Mass., barn, carpenter Norm Abram cuts holes in the old barn door to prepare it for the installation of new windows. Meanwhile, plumbing-heating expert Richard Trethewey shows host Kevin O'Connor the wall-mounted condensing boiler, and landscaper Roger Cook examines landscaping plans with homeowner Jeff Bernard and landscape architect Stephanie Hubbard. And in Spring Green, Wis., O'Connor meets with insulating-glass expert Tom Kaiser. On “Ask This Old House,” projects include removing backyard poison ivy without herbicides and weaving new cedar shingles onto the corner of a house.