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I am designing a 5'x6.5' loft bed. 4-5 years down the line, I'd like to be able to remove (or trim) and throw away legs ( and any under-bed furniture) and be able to use it as a regular bed afterwards. This is a DIY project.

This will primarily be used by my 5 year old, but should be capable of handling at least 1 adult's weight also.

I am looking for help to determine if the legs, as designed, would hold up for the purpose. If not, what would be possible leg design I could make up with 3/4 inch plywood that can do the job. I prefer to use only one kind of raw-material, because of limited tools I have available.

Design details:

Overall assembly is shown in following images:

full assembly-angle-1

full-assembly-angle-2

The legs are also supported at bottom as shown in first image. There will be one desk, one two-seat-bench and one long shelf above these supports. Behind all those furniture, I'll add additional vertical supports (at least 12 high") to legs, hopefully arresting any racking. Legs will not be bearing weight of any furniture other than bed frame.

Legs assembly and attachment are as shown in following image:

leg assembly

Each leg is L-shaped corner assembly of two pieces 64"x5.5" plywood sheets.

I have sketched up two possible corner joints as shown in second image: (left) with 6 inch thick laps/fingers joint with a 8mm dowel every 6 inches and (right) finger joint with 1 inch fingers.

Cleats are glued and screwed to bed-frame. Legs will insert into cleat+frame corners as shown. Legs will be bolted to frame with 8pcs M6 bolts in each corner. Frame will have a D-nut insert for each bolt.

I feel that rest of design would be OK, but I am not able to find any resources on strength of plywood in the configuration as being used in legs. So, not sure if legs would hold up.

[Update-1]

  1. Updated full assembly diagrams to show positioning of stairs, and internal structure panels added for arresting racking.

[Update-2]

  1. New leg design, made from 4pcs of 3" wide plywood arranged as a hollow square. How would this compare to a solid leg made of 4 pcs of 3" plywood pieces laminated together? I believe hollow tube would be stronger than solid core, if cross-section area is same (can't recall where I heard that)

hollow-square-leg

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    If the assembly is not secured to the walls (say in a corner), you may need some lateral/diagonal bracing to keep the assembly for racking in one or both directions.
    – Ashlar ♦
    Jul 24, 2020 at 23:57
  • Thanks Ashlar. I am not much worried about racking. I am actually concerned whether the let's will hold up the required weight, or if not, what is the best way to beef them up
    – GPS
    Jul 25, 2020 at 2:56
  • You won't easily be cutting box joints over this length! In fact it may be so difficult as to be impossible on a practical level. So yeah, definitely look at another option for the L-shaped leg assemblies.
    – Graphus
    Jul 25, 2020 at 6:04
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    Are you set on the idea of formal legs? Since you're using plywood you're missing out on one of its fundamental properties if you don't use it, at least in part, as a sheet material. If the back and rear use full pieces of ply (with cutouts for lightness and/or aesthetics) then there's almost no limit to the weight that rear corner can support, and racking becomes an impossibility for all intents and purposes. If you insist on using ply for the front leg then I would laminate up a sandwich of 3 pieces, that will make it nearly as strong as solid wood.
    – Graphus
    Jul 25, 2020 at 6:09
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    Agree that L-shaped plywood legs don't seem like a good idea. However, you could build them, see what you think, and add a stick of lumber (2x4 or thereabouts) on the inside corner to stiffen up the assembly. (Glue and screw the lumber.) 3x3 plywood laminate might work, though I'd consider assembling them in a way that has one of the ply segments perpendicular to the rest. (Ping back if you want a sketch of that.) All that said, you'd spend a lot less time (and only a bit more money) just using a 4x4 wood post.
    – Aloysius Defenestrate
    Jul 25, 2020 at 15:31

1 Answer 1

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The square legs would be considerably stronger than just the 2-sided legs, but honestly what is wrong with using 2x4's for the legs? You only have to cut them to length and you can nail 2 together for added strength if you want. On top of that you can cover them up with the plywood if you want to have that look, without all the trouble of putting finger joints in plywood. Now if you're using 1" plywood, maybe, but then the cost would be cheaper at that point to go with 2x4's and cover them with cheaper 1/4" plywood.

unfortunately I don't have numbers to back it up, but plywood legs makes me itch with 'not safe'.

the other issue I see, are not enough triangles to keep things from 'racking', unless you plan to run some lag bolts into the wall on 2 sides.

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  • Honestly I agree that just using solid wood for the legs would just be so much easier, and if painting the mix of materials doesn't even matter than much (although as you say you could skin with plywood for the look). But re. triangles and racking, if overall construction is strong and stiff enough there's no need for triangles, q. v. most hand-tool workbenches. I believe the wide central rails in the updated sketches have that well covered now, if fastened securely.
    – Graphus
    Jul 28, 2020 at 9:08
  • I guess the only place I'd have some concern about the triangles are on the 'front', Not a lot of concern, but some.
    – bowlturner ♦
    Jul 28, 2020 at 12:34

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