I'm about to construct a loft bed as in picture: it's 240cm long and 180cm wide (7.9ft x 5.9ft).

The floor frame is composed of 2 main beams (2x6) that run on the longitudinal direction, and 7 joists (also 2x6), one every 40cm, attached to the beams with joist hangers. On top of that is a sheet of plywood 21mm thick.

The main concern is about the 2 main beams: is 2x6 enough to support the weight of all the joists (2 adults) or should I use 2x8? Do you think the flooring is ok or should I run the main beams in the short direction and the joists longitudinally?

I have also attached a picture of the frame.

Loft Bed

Floor Framing

  • Hello, and welcome to Home Improvement. I think your 2x6 mains will be plenty strong, and you could go 2x4 for the joists. And, you should probably take our tour so you'll know how best to participate here. Commented Oct 29, 2019 at 11:00
  • Can you provide an estimated max weight for the people that will share the top bunk? Commented Oct 29, 2019 at 14:04
  • @UnhandledExcepSean The total max-weight of the two people is 160kg (352 lbs)
    – andrevall
    Commented Oct 29, 2019 at 15:27
  • This is overbuilt in my opinion. I bet 2x4's and 1/2" ply wood would be fine. The mattress will help spread the load.
    – JPhi1618
    Commented Oct 29, 2019 at 17:52

2 Answers 2


2x6 framing would be strong enough, but I have a couple of concerns.

  1. Racking - I think you should put a cross brace on the back (2x4 would be fine)
  2. Mechanical fasteners - for the elevated frame, you definitely want to use either lags or structural screws to attach it to the verticals. The rest can be nails and/or construction screws (largest that don't protrude through the other side).
  • Yes, though it's not clear from the drawing, the two main joists actually sits on top of lags that are on the internal side of the leg. Then I will attach them to the leg using 10mm bolts that go all the way through the legs and joist. Regarding the cross brace, do you think it would be ok to place two 2x4 horizzontally (for design purposes) or should I always place them cross?
    – andrevall
    Commented Oct 29, 2019 at 15:33
  • 1
    In my experience, cross braces are much better at making a structure rigid than horizontal braces. But, horizontal is better than nothing. Commented Oct 29, 2019 at 16:56

I once built a similar structure. 2x6 is more than adequate.

  • Thank you for your feedback
    – andrevall
    Commented Oct 29, 2019 at 15:51

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