I began constructing the perimeter by setting up the laser just high enough that the beam—representing the top of the joists / bottom plane of the flooring—just nicked the high (NW) corner. I Sharpie-d a blue line where the laser’s red sweep met the walls and studs. The results were in line with my earlier mockup.
To accommodate the wide range of vertical offsets from concrete to joists, I used several approaches around the perimeter. At the southwest corner is a short framed wall of 2×6 studs and drywall, full-height from the floor to the underside of the glu-lam beam that forms the front-back spine of the house. Using a box cutter and small brush saw I cut out the low end of the drywall and pried out the drywall nails. I lag-bolted a 2×6 as a band joist to support the south ends of the first 3 floor joists, first augering a through-hole to accommodate one of the bolts that anchors the glu-lam’s front column to its spread footing.
The west (front) end is a tall concrete foundation wall to hold back the front yard—the driveway actually slopes down toward the house, and the street beyond slopes up and to the right. This wall has an angled face. Here and on the north wall I freehand-cut PT 2×8 and 2×10 planks with a circular saw, and mounted them on end. The west edge is a nailer surface to support the first 16” of flooring. The north edge will support 16 full length joists (the remaining 6 will hang from the 45-degree angled joist that defines the high corner).
At first I thought of simply Tapcon-screwing the plank to the front wall’s angled face and beveling its top edge level as a nailing surface for the flooring—and chose the Tapcon length to match. But when I got into it I realized that the wall face had substantial variation—a straightedge laid horizontally near its base showed several significant hills and valleys. I decided to mount the plank vertical, blocked out from the wall with PT strips, and Tapcon it an inch or so up from the floor. Now the Tapcons were too short, so I counterbored and added washers.
Along the 28’ long north wall there are 3 separate conditions:
- Westernmost segment (near the NW high point): tall concrete wall similar to the west (front) wall, buttressing the west (front) wall.
- Middle segment: conventional mudsill, with finish floor level lower than the mudsill
- Easternmost segment: mudsill continues, with finish floor level higher
Near the high corner, the floor supports will be thin and custom-fit. On the middle segment I used the same tapered-plank approach as on the west wall, using a tapered off-cut to block it out from the wall because the top edge is below the mudsill.
On the eastern segment the plank’s edge is above the mudsill, so spacer blocks can be screwed to the mudsill. (This is a later picture with several joists installed and a sheet of flooring temporarily placed to move stuff onto the partly-completed platform in order to keep the work area clear.)
Along the east wall the new floor height is way up the studs, and this side only needs to support the last 16” of the flooring—not the weight of loaded joists as do the north and south sides. Conveniently, the east edge of the 28’ long floor will come within 2” of the studs, so I lag-bolted a 2×4 to the studs and screwed a 2×4 to the top, forming an edge nailer.
(The fixture cantilevered from the wall is a wedging table for preparing clay for forming. It’s 3.5” thick cast plaster— super-heavy, so I didn’t want to detach it until absolutely necessary to install joists and flooring beneath it. It normally has 2×4 vertical legs but I thought I’d be clever and get those out of the way so I’d have clear space below when mounting the joists. Later, when actually about to start work under that 150+ pound slab, I had second thoughts and replaced the diagonal strut with a temporary cross-beam mounted to the side wall—see later photos.)
-- Accomplish the great task by a series of small acts. (Tao Te Ching / Lao Tzu)