by KCStudly » Wed Nov 22, 2017 3:42 pm
You don't need 3/4 or even 1/2 inch thk splice ribs. The thickness of the plywood dosen't add any strength to speak of in that direction, it is the thickness of the wall, the "width" of the plywood splice pieces that determines how good they will be at adding stiffness (flatness) to the wall panel. Sure a 5mm (3/16 thk) slat of plywood is pretty floppy when you wave it around by itself in free air, but when you constrain it between two pieces of foam that prevent it from bending in the y-axis (thin way) and only apply side load on the wall in the x-axis (wind, a tree branch or somebody standing a ladder up against it), then that 2 inch width of ply acts the same as a 2 inch stick of lumber, stiff as a board.
Truth, you don't even need the slats at all. Leave the foam in larger sheets so that there are a lot less butt joints to cut, align, clamp, glue, scrape, sand, and repair after you sand into the foam too far (the foam sands so much easier than the wood, or even the glue, that it is very difficult not to over sand the foam).
Make sure you leave a fair amount of depth in the header over your rear door, as that will be your only "shear" panel there. I would look for at least 4 inches, 6 would be better. If you don't want the roof that high you could use a "slouchie" height door. You can also help gusset the wall to roof joint by building over head cabinets in along your side wall seating/bedding/kitchenette areas.
I'm not sure I understand your section diagrams. What is 4 inches thk? I'm very pleased with how rigid my walls are with 1-1/2 inch thk foam and 5 mm interior ply skins (even before adding the outside skin). I would think that 4 inches of foam would be excessive, unless you plan to do a whole bunch of sub-zero camping. If you are worried about the width and height of your front wall and being able to withstand wind pressure during travel, you could use a standard thickness wall and consider stepping up to a thin ply veneer, or just add a couple of foam ribs, like pilasters, covered with PMF.
The YJ looks like fun. Are you going LS or old school SBC?
Last edited by
KCStudly on Mon Nov 27, 2017 7:03 am, edited 1 time in total.
KC
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