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Hope that this is the right forum for woodworking design critiques. I'm experienced with plywood but this is my first time attempting 'sturdy' furniture. I'd like to make sure it's going to be strong enough to hold up. As it's a Q+A site, the main question is: Is this design strong enough to function as a regular use dining seat? I can separate in to separate questions if appropriate.

Sourcing reasonably squared lumber is surprisingly difficult but my local depot has what looks like decent planed pine @ 44x69x2400mm that I'm considering using.

There's a few considerations to the bench design:

  • It needs to be self supporting as I can't attach the frame to the wall. The wall is clad with 100mm insulation board and I can't drill through to the brickwork. I will certainly put 'noggins' in to keep it held against the wall to stop it rocking. There are walls on the back and both sides.
  • I can only screw in to the floorboards but no deeper as there is underfloor heating below the floorboards.
  • I've left the bottom open at the front because we want to make deep pull-out storage drawers on castors for toy storage.
  • I'm planning on cladding the frame with 12mm birch plywood and using 18mm birch plywood for the top.
  • I'm assuming we will seat a max of 4 people on this so worst case ~400kg load spread across it.
  • I'll be using 18mm birch ply for the lids / seats. I've allowed for a 34mm overlap on 3 sides of each lid and a slight overhang on the front to easily open the lids. I'll secure with piano hinges at the back and use pistons with soft close for holding the lids open.
  • I'll use pocket hole screws and glue for the joinery
  • As I discovered when installing the kitchen cabinets, the floor is far from level, I haven't yet figured out how to compensate for this. The floorboards run from front to back on the window seat.

Pictures/dimensions

Frame: frame

Frame with cladding and 100mm deep top storage. All cladding made with 12mm birch ply frame with cladding

Frame with cladding and lid: Frame with cladding and lid

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  • The biggest thing I'd worry about is racking forces. Are there going to be walls on either side of it in the final installation? If not, I'd consider adding some kind of diagonal bracing. It looks plenty strong in compression, and there's certainly not going to be any noticeable sag using beams that big and 3/4 ply for the seats.
    – SaSSafraS1232
    Commented Aug 21, 2018 at 18:24
  • Yeah, there's walls on either side. I was planning on 'filling' the gaps to the wall with noggins to help brace it. I'll update the question with info.
    – beirtipol
    Commented Aug 21, 2018 at 18:26
  • 2
    Plenty strong enough. Anywhere there's a plywood skin it prevents ALL racking in that plane, this is the principle behind many modern workbenches.
    – Graphus
    Commented Aug 21, 2018 at 18:34
  • @graphus - good point on the plywood skin. Should I put a full panel on the leg pieces to prevent them skewing or would that be Overkill?
    – beirtipol
    Commented Aug 21, 2018 at 19:48
  • @Graphus he doesn't have a continuous plywood skin on the front or back. It could still rack left-to-right. However, in his comment he said it would be enclosed between two walls, so it looks plenty strong to me.
    – SaSSafraS1232
    Commented Aug 21, 2018 at 20:33

1 Answer 1

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In terms of compression strength, I wouldn't want to park a big car on top of it - but even a couple of drunken teenagers jumping up and down should be fine.

As others have commented, racking side-to-side might have been a concern if you didn't have walls either side. That could easily be addressed by attaching a plywood skin to the back (but it doesn't need to be 12mm; 4mm would probably be enough if it is thoroughly glued to the frame).

Racking front-to-back is a slight concern - I would probably make sure some of the frames had a plywood skin (perhaps three out of the five?). If you screw to the floor and back wall, this won't be necessary, but personally I would make the seat rigid, and then leave it free-standing. Doing so will make it much easier to move for cleaning, or refinishing the floor.

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  • I would think you wouldn't even need 4mm plywood and glue. I've put together plenty of flat pack furniture over the years and they give you folded pieces of 4mm(ish) cardboard that you unfold and tack into place with tiny nails to provide rigidity. I've got some tall, narrow DVD cases that are not wobbly in the least because of this.
    – FreeMan
    Commented Sep 7, 2018 at 13:28

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