Can I use two 2x4's to replace 4x4 posts in a loft bed?

Question

I'm building a loft bed for a queen size bed. I planned to build a platform and support it with 4x4s, but I'm having trouble finding untreated 4x4s. I plan to loft the bed 5' or so. The platform will be made of 2x6's covered in 1/2" plywood.

This shows what I'm planning to do:

Can I use two 2x4s instead of the 4x4's to carry the load?

If so, will nailing/screwing them together in several places be sufficient to hold them together?

I'd like to use 3/8" bolts to join the platform to the posts (for easy disassembly). If so, should I only bolt down the long side of the platform, or try to place bolts on both sides of the corner? If the latter, how should I put a bolt through the narrow side of the joined boards?

Answer 1

2 2x4s are not square, if that matters (3 x 3.5). They will be plenty strong as assembled posts.

Try a traditional lumber yard, they will have untreated pine. Cedar may also be an option.

Your structure would be better supported if you shortened 1 of the 2 paired 2x4s at each corner and made a jack-king stud arrangement like a door frame and header. The main tenant of construction is to bear the weight with structural components and only use fasteners to keep the structure in place, not to bear the load (in shear).

You are, in effect, making a small deck. You should attach the rear 2x8 2x6 to each wall stud. A 4" #10 decking screw would not be too small .

The front and rear members are, in effect, beams and should be 2x8s. The joists running perpendicular to the beam should be 2x6 2x4s hung with joist brackets.

Answer 2

If you are going to use 2x4 instead of 4x4's as "beams" I'd set them on edge. If you glue and nail them that will be stronger than just nailing them together. I'd also consider using a metal bed frame with the legs removed on top, rather than plywood (as long as you're using a box spring). The plywood is going to sag a lot across that span, enough that the side walls are going to tilt in in front. Also, this thing is going to want to rack over without corner bracing.

But really I think you're reinventing the wheel quite a bit. You could modify standard framing methods just a little and get something sturdy. Google around "platform framing" "balloon framing" "post and beam" and get some ideas from centuries of carpentry.

Answer 3

You need to put the 2x4s on edge, not flat. Consider a large, soft covered book. We used to call them phone books, but no one knows what they are any more. Hold the book with the spine in one hand, and the open end in the other. Give the book a bend. You'll see the pages separate in the middle.

The same thing happens in a beam. So if you lay the 2x4s flat, you'll get the same effect. (If you have to lay them flat, you must clamp and glue them.)

I also have some concerns with the way you are mounting the beams to the walls. You're asking your connector to support the entire load. I'd much rather see the studs rotated 90 degrees, as in traditional wall framing and have the beams run on top. Use a connector, such as this:

You might be able to find something a bit more decorative at a specialty hardware store.