We then turned our attention to the gable-end wall of the main house. At the bottom, the cladding extended down into the space that would be occupied by the slab, so we decided to complete all of the demo first. After laying tarps on the slab fill to catch the debris, we stripped the wall down to the studs, removing the three-coat stucco, metal lath, building paper, plywood sheathing, and fiberglass batt insulation. We then poured the slab used 4,000-psi concrete with welded wire mat reinforcing. After it was poured, it needed to cure for at least 28 days before we could begin installing the radiant tile floor.
To complete the window openings, we built short, 17-inch-high walls between posts, then sheathed them and the posts with Zip System panels. Next, we waterproofed the walls by taping both the sheathing seams and the rough sills with Zip tape.
Next, we mulled the French casements and fixed transoms on site using Marvin’s mull kit. We had never used this mull kit before, but it was surprisingly easy to figure out. Once mulled together, each window assembly weighed about 150 pounds, and we needed two men to lift each one into position. After checking for plumb and level, we tacked the windows in place. We wanted to be able to adjust them after they were all installed to ensure that they were properly aligned, which would make the interior trim work go smoothly. Once all of the windows were permanently fastened in position, we applied a strip of Zip tape at each jamb, running a few inches above and below the window frame, then ran a strip at the head flashing. After finishing each window, we rolled all of the tape with a J-roller to set the adhesive.
After the rough wiring was completed in the sunroom, we insulated the knee walls, the open space in the posts, and the stud bays of the gable-end wall of the existing house with “Thermoseal” open-cell spray foam (hitting the gaps at the windows with low-expanding foam). We sprayed the whole roof assembly as well, leaving the sunroom’s ceiling uninsulated. After hanging ½-inch drywall on the posts and all of the walls, we converted the two exterior doors in the existing gable-end wall into interior doors. This involved removing existing weatherstripping and the exterior sills
We installed 1x6 finger-jointed pine bead board on the sunroom ceiling, and used poplar for window and door trim. To match the profile of the windows, we milled a decorative bead on the casings. This complicated the window trim at the intersection of the mulled jambs with the trim at the post…
…so we miter-cut the mull jambs—chiseling out the extra material—to receive the 1 1/2-inch-wide horizontal mull trim
Installing the curved molding at the doors was tricky. As it turned out, the radius was not true, so we cut three pieces of wide, poplar stock close with a jigsaw and then installed it and used a flush cutting bit on a router to follow the irregular radius.