First, using construction lumber means LOTS of splinters. And knots. And cuts/gouges/nicks.

Second, the link info does not work.

Third, I hope there is a wall(the darker area on the right) since there is no way a 6'6" span will stay up unsupported on the right end. Unless it is fastened to a wall.

Fourth, construction lumber cannot be fastened long term to a wall unless you use huge washers and 3/8" or larger lag bolts. The wood is just too soft.

Lag bolts should be fine for attaching these to the walls. I agree w/HM that you'll need 3/8" lags and large washers. The drywall won't support any significant amount of weight, so the lags need to be rigid (i.e. thick) enough to not bend under the load. 4" long is probably good. When lagging the frames to the walls, you'll almost certainly find that either the walls, the frames or both are not straight, so they won't mate cleanly. The bolts may be strong enough to pull them together, but doing so will distort the frames and could stress other joints. You'll probably be better off if you use shims to make up the differences instead.

Corners could be either LONG screws from the outside (because screws going into end grain are inherently weak) or pocked-screwed from the inside. Angle brackets suck.

2X6 is plenty.

19" cantilever should be fine. It's not clear how you're supporting the far end of the 78" side.

Mattress support is not clear enough to critique.

Thanks handymac and John. The right side is a wall; the color just didn't show up right. With the 11" or so of open area near the wall I plan to put some shelves.

I'll go with 4" lags and large washers then. For the connections into end grain, I'd like to get the strongest connection possible. I'm just not sure what that is. How about one of the hardware options show in the link below?

Here is a link that might be useful: Bed hardware at Rockler

Doug fir? You should get Clear Vertical Grain, Kiln Dried. Expect to pay about $7 a foot for the 2x6.

As an experienced woodworker and carpenter I wouldn't even attempt to make the project out of ordinary construction lumber. Sap, knots, defects, and shrinkage will be your first adversaries. Then how do you give it a good looking finish?

Your design looks good. I think the location of the 4x4 posts for the ladder are ideal to support the weight of the beds.

For the corners, I would face screw from the outside with long screws. If the assembly is permanent, use wood glue, counterbore the screw heads and install wood plugs to fill the holes. CVG fir has a straight grain pattern that make it easy to hide wood plugs by lining up the grain. Cut the plugs flush, sand and finish the bed frame after it's installed.

For the matress suppport, it's all in the plywood you select. 3/4" ply supported entirely around the edges with a cleat is fine for a single mattress. Use rated plywood if you want to make it extra strong; 3/4" subfloor, MDO, platform grade, or baltic birch would be a reasonable overkill. (Baltic Birch if you want to go with a nice stained and finished underside)

No offense but I would reconsider the whole design. The vertical ladder is an accident waiting to happen and if that is the only window in the room, aside from being "illegal" in many municipalities, it is also dangerous to block it such a way. Your choice of material is a bit of overkill too. What are the dimensions of the room? Ceiling heights, window and door sizes and locations? Any photos? Your kids are going to be getting older and bigger too and the design doesn't seem to take that into consideration. Judging from the pictures there is no room for a teenager to sit up in bed.

The bed hardware pictured is designed for use with hardwoods suitable for use as bed rails. Oak, ash, mahogany, maple, and so on. That hardware will NOT work with soft woods.

IMHO, even disregarding the window, the whole thing would collapse shortly. You need four posts for the double bed. Why is the single bed up high?
Also, putting lag bolts into your 2x4 studs would not be a good idea. You would need to go into the wall and put a wide cross bracing between the studs. If you want to put a closet or something under the single bed, make that part of the support system. I believe a free standing system would be better.
Of course, as usual, I may be wrong.

The beds are supported by walls on 3 sides.

Only one post is needed; the one on the left side of the ladder is located ideally for support.

Depending on how goofy your kids are and if they are going to hurt themselves, well I guess that is up for debate.

The requirements for bedroom emergency egress are minimum 20" wide and 24" tall, unobstructed opening to the outside. The sill can be no higher than 44" to the floor. The total clear area must be at least 821 sq inches. Therefore a 20" x 24" opening will not pass. 20" x 41.5" is the narrowest opening allowed and 34.5" x 24" is the shortest allowed to meet the minimum area of 821 sq inches.

Thanks for the input everyone.

aidan - I was planning on using construction lumber, but I could be talked out of it, especially if the alternative is stronger. I was planning on sanding, using a round-over bit on exposed edges, and just applying a coat of poly.
As for the mattress support, I was thinking of using a cleat and some 1x slats across. Do you think I could skip the slats with 1â plywood?

Long screws - the weakest point to me is the intersection of 2x6âÂÂs on the right (not in the corner). What type of long screw should I use and should I use 2 or 3 into the endgrain of the other 2x6. And again, if there is anything else to strengthen that connection (e.g., angle bracket on the inside), IâÂÂm all for it.

jey - the window you see is not the only window in the room. My drawing didnâÂÂt show the other 2 windows. Here is an updated drawing from a slightly different angle. Though, I have been thinking whether I should put a railing (or something else) in front of the window near the bed for safety reasons. IâÂÂm allowing for about 30â from mattress top to ceiling, which is a little tight, but I wanted more room below.

handymac - thanks for the info on the bed hardware. Makes sense.

someone - would the ledger boards (3 sides) really not be that strong if lag bolted into the 2x4âÂÂs behind the walls? I was planning on 2 lags at each stud. Seems like it would be stronger than a freestanding bed with posts and cross-bracing, but IâÂÂve never done this before. IâÂÂll have railings for the beds, but I havenâÂÂt designed them yet.

An old violin maker once told me; "You have 100 makers make a violin. They will make it 100 different ways and all will say their way is right." With that in mind, I will tell you how I would start out. I would cut out a strip of drywall for each bed, the width and length of the bed frame. Then I would nail bracing to the studs, making bracing plumb and level to eliminate most shimming when the bed frame is nailed or screwed to it. That's if I were using your design.
For sure I would not build the single bed across the window
Having kids, I can envision your son and three of his friends sitting on the edge of the bed. Will it hold up?

Perusing the internet I saw a video on Youtube/bunk bed/DIY that shows how to make a bunkbed with posts. The tools used were a chop saw, a circular saw, a chisel, a drill and screwdriver. The wood was pine. These beds could be attached to your wall easily and would be sturdy. If you wanted to get a little fancy you could join the rails with double through, wedged mortises or something like that. To save money you could make the 4x4 posts out of 2x4's glued and screwed together.

I don't have time at the moment to discuss all the issues here, but our daughter slept on an elevated platform bed till she was ten and the platform did play duty for a while after that.

Ours was attached to the wall on three sides, but the supports were only 2x4 and they were ample (over drywall), attached with #12 screws perhaps 3 inches, 3 and a half inches, long. I am not sure there is an advantage to using 2x6s because it's a shear force that's involved. When I took the whole thing down after 12-14 years, there had been no shifting of those boards.

We had a plywood platform with the front supported with yet another 2x4 across. This was screwed into the ends of the wall 2x4s if I recall correctly. Total length was 8 and a half feet, and it required a post to avoid sagging (at least to avoid creaking, and it's an old rickety house - didn't want to stress it too much). Screwing the plywood to the wall supports is actually what holds the bed to the wall, I think. There is your force downward, and your force outward.

The problem was never with children up there sleeping. It was when three friends came over, all heavier than my own kids, and all decided to go up there, boisterously.

Your right angle portion is a bit challenging. Weight considerations aside, I foresee many heads (especially adult heads) being bumped on that protruding corner, maybe with corresponding shin bumps below. Me, I'd put a post there just to avoid the risk to my head when I'm making the beds.

Another thing to realize is that your front edge support on the long portion can go all the way across; it need not end at the corner. This may give you another construction option.

Your foot boards on the ladder look narrow, ouch. Plus, a slanted ladder may be better. So maybe separate the functions of support post and ladder.

KarinL