My goal was a level floor supported by 2×4 joists. But the concrete floor’s compound slope steepens even more toward the highest (northwest) corner. If I started the joist frame in that corner, the finish floor would start 4.25” off the concrete at the highest point (3.5” joist + 0.75” ply). That would cut into my desired minimum 8’-0” headroom—and I’d pay that 3.5” penalty over the entire 12’ x 28’ shop area, with a step-down of 15”-16” at the far edges.
To avoid this I decided to special-case the high corner, and start the main joist frame one 2×4 height (3.5”) down the slope in each axis. As it turns out, the initial down-slope was about equal for the first 8’ or so along each wall, and by 8’ out there was 4.25” available. A 45-degree band joist, supported just off the concrete, would define a right-triangle corner within which I’d custom-frame the floor support, possibly with short tapered PT sleepers.
Simpson makes 45-degree left and right joist hangers—for 2×4’s they’re the SUL-24 and SUR-24. About $5 each (vs. $0.75 for the 90-degree type), but I’d only need a few in this corner and one other.
With various shorter 2×4s on hand in addition to the 20 12-foot joists-to-be, I decided to do a quick mockup. This would also let me (and my partner/”client”) visualize the two-steps-up edge and the car-door clearance. Nothing like a visual to help with client buy-off :)
Framing mockup showing “high corner” diagonal joist, and cross-beam joint supports at the 4’ and 8’ points. NOTE: Some joists stick out into the foreground because I didn’t want to cut them for the mockup.
View across the workshop’s short dimension, with mocked-up step:
Car clearance to step. Just enough to comfortably walk past with a bicycle or one of the City’s big recycle/compost bins:
Now to start framing the perimeter…
-- Accomplish the great task by a series of small acts. (Tao Te Ching / Lao Tzu)