Recently, I moved into a small house with a roommate, after years living alone. In my old place I had a workbench in what would normally be a dining room, a computer desk in my living room, and a whole separate room for sleeping. It was obvious that I wouldn't have floor space for all that in one room. What to do?
Enter the 3rd dimension!
This queen size loft bed/desk combo gives me what would otherwise be an impractially enormous (2.2m long by 1m) desk all in space that would otherwise be wasted by a normal bed. It's big enough that I can use the left half for my computer, and the right half for an electronics and hobby work bench.
Step 1: Planning
I generally don't like to overplan when I'm building things, but in this case I wanted to at least generally figure out how it was going to fit together, and more importantly, to make sure I would have room for a desk at a comfortable height, and not be crowded up against the ceiling when I'm in bed.
I measured how high a desk should be for me, and how much room I needed to sit up in bed, and drew it in sketchup to see how it looked. I used a couple tricks to save some height in the design, which I'll go into later, but it seems like it'll easily fit. (I'm quite tall, so I expect this design will work for anyone)
I've attached the .skp if you want to modify it for your own. The actual heights on mine are 67cm to the bottom of the desk, and 130 to the bottom edge of the side board. The drawing has it at 63cm, which would be the absolute minimum that my knees fit under, but you should probably adjust it to whatever's comfortable to you, or make the cross beams much lower, so you can shim the desktop to whatever height you want.
Step 2: More Details on the Design
I didn't want to get too fancy with the woodworking here, since this is a really utilitarian design. I wanted it to be very solid, reasonably inexpensive, and buildable with mostly ordinary construction tools. I also want to be able to disassemble it if I ever need to move it out of this room.
I decided that 2x4s would be the best way to go, and I built it as 2 end pieces with the side boards and desk bolted in between with lag bolts.
I don't like using bolts or screws against sheer forces, because a loose bolt can allow things to shift and crack the wood, so I designed it so everything is directly supported by sitting on top of a strong board. Nothing is held by just bolts or screws.
I'm actually building the vertical posts out of 3 sandwiched 2x4s creating a pseudo-tenon joint for the desk supports, and all of the pieces that look like 4x4 boards are just a pair of 2x4 glued and screwed together.
To save some vertical space, I supported the front edge of the bed slats using a piece of metal angle, instead of another 4x4, and I laminated together the desk out of boards, so it's fairly thin, but very strong and stiff.
Step 3: Buy Your Materials.
I counted how many boards I'd need while looking at the sketchup drawing and went to find a lumber yard with some decent looking wood.
The 2x4s weren't too much of a problem, but all of the 2x8s they had were cracked, twisted, and banged up. They really didn't look usable for this kind of a project. Fortunately they had some very nice 2x10s, and nothing in the plan interfered with using them. I would simply have to cut a few supporting boards shorter so everything ended up at the same height in the end.
I also used ordinary yellow wood glue, and a big bag of deck screws long enough to go most of the way through a stacked pair of 2x4s. I used desk screws because they were available by the pound for cheap, instead of overpriced little bubble packs. Ordinary wood screws are fine. Also, since they're mostly just there to hold boards together while the glue dries, drywall screws are fine too. Whatever's cheap.
Step 4: Build the Ends
I used a chop saw to cut the boards, but you could get by with a circular saw too.
I used various combinations of screws and clamps to hold things together while glue dried. I actually built this in the evenings after work for a couple weeks instead of trying to get it all done at once, so I generally had time to let the glue dry a few pieces at a time as I built it. While assembling the H shaped frame, you can measure corner to corner to make sure everything is square.. if your measurements aren't equal, it's out of line. There is one odd shaped board shown in the picture that I had to notch out a corner on with the handsaw. I'm sure there's plenty of other ways you could work around that problem (It's called "end rail" in the sketchup drawing), but I figured it wasn't too difficult this way.
I glued the whole end together as one piece, so it's very strong.
Step 5: Bolt in the Side Boards
Next I predrilled and bolted in the side boards.
Also, not shown, I added a 3rd lengthwise board near the floor, just to give some extra strength to prevent it from tipping like a parallelogram, or the legs spreading. The way I have my desk bolted to the frame will help with the 2nd issue, but not the first.
If you are using narrower boards for sideboards and supports, you may want to put some in as diagonal braces on the back to prevent racking. With these 2x10s it's rock solid, so there's no need.
The 4x4 beams that hold the slats up are trapped between the end boards, so they don't need any heavy bolting or screws to keep them in place. I just used some metal brackets I had kicking around to keep them from sliding. They definitely need to be held in place, though, so the slats can't fall through.
The slats I used are just ikea ones that I took off my old bedframe. They're stapled to a strip of fabric, which makes them more convenient to handle, and keeps them from sliding around, but I still screwed every 3rd slat down, just to make sure they couldn't shift too much and fall out of the frame. The front metal slat support (I used aluminum) is screwed to the side boards with a lot of screws (every 10 cm), so they definitely won't pull out. The ends are also held up by sitting on blocks, but a lof of the weight is carried by the screws into the board, so more is better.
Step 6: Desk Top
I made a solid wood top by laminating a bunch of boards together edge to edge, and then planing the whole thing smooth. The results are nice, but it's a huge amount of work. If you want a much easier alternative, use plywood. You'll want to brace it so it won't sag in the middle (2.2m is a very long span), or you could spread some glue, and laminate 2 sheets of 3/4" into a 1.5" slab if you prefer the brute force overkill method. (I know I do!) Next, do something to roundover the edges, especially if you're using it as a computer desk, so the sharp corners won't dig into your wrists.
I coated the whole desktop with polyurethane so it won't soak up spilled drinks, food, and dirt.
Next, bolt the desk on top of the end braces of the frame. It helps support the front legs so they can't move around, and makes sure that your desk won't shift or fall off the supports.
Step 7: Extras
It was obvious that I was going to need to add some lighting over this desk, since the bed will be blocking the light from above. I decided that rather than desk lamps, I'd build in some fixtures for LED light bulbs.
Since I was going through the trouble of wiring it anyway, I also added a few more 3 gang electrical boxes with outlets so I can avoid the usual mess of power bars and extension cords.
I wired up the leds on dimmers (I did 2, one string of daylight bulbs, one of warm white) it's not super efficent, since a lot of the light is blocked by the placement of my computer monitors, but they're LED bulbs, and I usually don't need a huge amount of light on my desk when I'm using the computer anyway. Where I have them mounted on the back of the centre beam, they don't shine in my eyes
I later added another fixture with a spot light bulb pointing straight down above the right hand side of the desk where I do a lot of soldering. It helps a lot having really good light.
You might also want to build in a ladder. I haven't bothered, and just step on the end of the desk and climb up, but I think for someone less tall than I am, a ladder would be much easier.
Step 8: Load All of Your Junk on It.
Since I built my desk 1m deep, it leaves an extra 40cm of space behind the desk, which is perfect for some big floor standing speakers, and my bass guitar cabinet . Because the desk is so deep, I have lots of room at the back for my electronics equipment, and lots of room in front to actually work in (when I clean all the random junk off). The amount of space it's saving me is huge.