Bracing to create a garage hanging loft?
I tried adding this to an old thread, but don't think anyone is going to find it there so I created a new topic.
I have a similar shelf I need to build. I would appreciate any comments or suggestions about how to properly construct it. I have 2 pictures showing the same design with the rafters going in different directions.
1. This is a hanging loft shelf 10' wide by 4' deep
2. It will hold storage boxes, nothing very heavy
3. It will mount against the wall above the garage door opening
4. There is a wall to the left 2' from the shelf. I could extend the shelf if needed to use that wall, but then I have to deal with a 12' wide shelf
5. The ceiling is supported by a huge I beam and is the floor of the bonus room above
6. Should the shelf rafters go left to right or back to front?
7. Should I double up the front 2x4 or use a 2x6 as shown? I'm wanting the extra space since there is the garage door opener rail below the shelf, so leaning towards the 2x4.
8. Should the top hanger rail be just a 2x4, or should I bolt 2 2x4's together on the 4" face, then bolt them to the ceiling rafters over the sheetrock, and then bolt my hangers to the 2" faces?
9. Am I ok on the 10' span without having to double up or put a middle hanger in there?
10. And what about the back mount? I have a top plate there using a 2x4 for the shelf to sit on and then bolt the back shelf 2x4 to the garage wall. I also have to put 2x4's between the vertical beams because they sit out 1.5" from the wall. So the 2x4 spacers would make a flush mounting surface. I then would have to be careful of where the mounting bolts for the 2x4 spacers go since the shelf back 2x4 has to mount to the spacer. So my idea is to bolt the spacer to a vertical beam and then bold the shelf back to the spacer anywhere in between.
For the front beam a 2x6 will sag less than 2 2x4. A 2x6 supported on the ends as you indicate will take up to 20lbs/sq foot. The math says you will get just over 1/4 inch sag in the middle.
The calculations on bolts/wood tear out is very complex. On the bottom end of each hanger you have plenty of wood to place nails/bolts. On the top you only have 1 1/2 inches. The key failure will be the top of the hanger board splitting vertically and sliding off the nails/bolts. If you put 2 2x4 into the ceiling rafters you would get 3 inches rather than 1 1/2 to nail into.
Going to have to move the 2, 2 X 4's your using for hangers so there on the outside not on the front. That way there's more surface area to bolt to.
Use at least 1/2 carrage bolts.
Agree on the moving the end 2x4 but 1/2 bolts cause a issue. Although you might get by with 1 bolt if you try to use 2 you will not be able to space them properly so smaller bolts may be required.
Looking at the 2x4 hanger on the bottom end. The first bolt must be placed 3.5 inches ( 7 bolt diameters) from the bottom to avoid splitting and the second bolt needs to be placed 2 inches (4 bolt diameters ) above it. The problem is if you align the bottom of the 2x4 hanger with the bottom edge of the 2x6 horizontal member it puts lower bolt in the middle of the 2x6 which is fine but the top bolt would then be above the top of the 2x6. To fix this you would have to allow the 2x4 to extend below the 2x6. The lowest the bottom bolt can go in the 2x6 is 2inch which mean 1.5 inches of the 2x4 hanging below.
a couple of 1/4 in bolts are more than strong enough and the spacing is much easier to accommodate. 3/8 bolts would be the largest possible and still align the bottom of the hanger 2x4 with the 2x6
When it comes to wood and bolts more and larger is not always the correct answer.
I'm a little unclear about moving the front 2x4 supports to the side. Maybe this depends on whether I use front to back or side to side rafters? Should I used 3 10' 2x4s going left to right or several shorter ones going front to back (second picture vs. first picture)?
Also, I think it is not clear from the picture angle and colors, but if you look closely at the gray area of the ceiling, it is supposed to show the hidden rafters and the sheet rock with a 2x4 (or two stacked together) running left to right on the exposed ceiling above the shelf where I was going to bolt the 2x4 hangers. You can see my "top plate" 2x4 running left to right on the ceiling where the hangers go up to mount to it.
I guess I use side to side rafters, and the front 2x4 or 2x6 is 10' long, then my side 2x4s would be 3'9". If I bolt the bottom of each hanger into the front, then the 2x4 hanger indeed would either have to slide "in" a bit towards the center to avoid where the side 2x4's are screwed to the back of the front board at the corners, or move to the side and connect to the short 2x4's. But if I do the latter, the boards are now turned 90 degrees and I have a problem bolting them to the top plate in the ceiling which has to run left to right to span the rafters in the ceiling as shown in the diagram. Either that, or I would have to put 2 top plates running front to back along a rafter and recompute my measurements to have the width of my shelf hit where a beam runs above it.
I would not worry a real lot about the exact placement of the lumber between the front and back it does not do a lot structurally mostly something to nail your plywood into. If you were to use 3/4 plywood you could almost get away with just the front and back and no lumber inbetween. 3/4 plywood is rated to go 4 feet if this was a roof. Note this assume you cut the plywood so the grain run front to back in your case.
I would suspect the simplest thing would be to run the support lumber front to back and move the sides in 6 inch or so. You could just leave the far edge of the plywood unsupported. If you decide to use long members and go side to side you should only need a single joist since it would be the same as a floor 2ft on center.
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