Lofty goals: RavenMini deLuxe build - day 4
This will be a short session, I’ve got to cut class early. Today I’ll be installing the two rim beams, hanging the loft floor joists and installing the loft floor plywood.
Let’s get to it
The first task is to measure and cut to length a 2x6 that will run across the top of the back wall, on its edge, against the plywood wall sheathing. I use 4” screws spaced every 2 feet through the underside of the wall top plate to pull that 2x6 tight to the plate.
Then measure and cut the 2x6 planks I’ll be making into rim beams: the overall front-to-back dimension of the loft needs to be 12 feet, so I need to remove 3 inches from my 12 foot long boards (to account for the two 1-1/2” boards capping each end of the rim beam; the plans show you how everything is arranged).
I build the two rim beams by laminating pairs of 141” long 2x6 together with rows of 3” nails (or screws) every 16 inches.
The two rim beams go up on top of each side wall, and are secured in place with pairs of 4” screws every 24 inches, up through the wall top plates.
You’ll notice that I left the plywood wall sheathing extending up past the top of the wall, in order to tie everything together into one strong assembly; I use 2” screws to attach that plywood to the sides of the rim beams.
I then cap the front ends of the rim beams with a 12’ 2x6 that has been trimmed down to 143” (remember, the side walls - and therefore the two rim beams - are 143” apart, so that the 1/2” plywood on each wall finishes the walls off to 144” (12 feet).
Next is laying out the position of each of the loft floor joists. Measure from the back of the building along each rim beam, hooking the tape on the back end of the beam (not the plywood), marking a line every 24 inches, with an ‘X’ toward the front of the building, to remind you which side of the line the joists will be positioned.
If you’ve been careful to make your side walls perfectly parallel to each other and perfectly plumb, the measurement between the rim beams should be the same all the way along their length (give or take an 1/8”).
Measure and cut all the joists and start lifting them into place, aligned with your layout marks
The plans call for joist hangers supporting the ends of each joist, and for a beginning builder I strongly recommend the added security that they provide. I chose not to use hangers here because there’s a 1/2” supporting ledge at the wall top plate, and using three 4” long structural screws to attach each end of the joists to the rim beams. I feel quite confident that everything will be sound without hangers in this low-load situation
Once all the joists are in place, I check the diagonal measurements across the rim beams (just like I did with the walls a couple of lessons ago), to be sure everything is still perfectly square. I had a small discrepancy because the front end of the side walls were leaning slightly off plumb, so I used a ratchet strap to pull them straight until all the plywood on the front wall and loft floor is installed.
Last step is installing the 5/8 tongue & groove plywood for the loft floor. I used 2-1/2” screws but no subfloor adhesive, since the underside of the floor will remain exposed, and I want to keep it all clean and pretty. The floor may develop a squeak or two, but I can live with that.
Voila! Now you can stand way up high, and get a feel for what your view will be out the loft windows. Pretty sweet.
Next lesson: cutting and installing roof rafters. Get ready to learn some simple geometry, care of our old friend Pythagorus (don’t sweat, if I can do the math, anyone can. I’ll show you how).