Work on the Concord, Mass., barn-conversion project includes installing an underground PVC conduit for 200-amp electrical service. Meanwhile, carpenter Norm Abram and contractor Tom Silva push out an old roof section to let light in; carpenter Jason Wood cuts a hole in the roof to accommodate a dormer; and host Kevin O'Connor interviews architect Sarah Susanka, the author of “The Not So Big House.” On “Ask This Old House,” projects include a backyard drywell for rainfall from roof gutters and a bathtub safety grab-bar. Also: O'Connor, Silva, heating-plumbing expert Richard Trethewey and landscaper Roger Cook guess the uses of unfamiliar objects.