In the past I have sistered lumber by putting the two pieces side by side (so if you have two 2x6s putting the 6” side next to each other) with some liquid nails on them and then putting some nails through them to connect them.

But now I’m in a situation where I’d like to join the 2x4s on top of each other - so essentially taking two 2x4s and creating a 2x8 from them.

At first I was thinking I would just get some Simpson nail plates and go all the way down the length of the seam where the boards touch on both sides, but I was worried that wouldn’t provide enough support. My other thought was to run a ~6” piece of 1/2” plywood the length of the seam where the boards touch on both sides and put nails through the plywood and 2x4s to connect them

Would either of these methods work for connecting two 2x4s on top of each other? Is there a better method that I should use instead?

  • glue lamination is a thing, where they glue smaller buts of wood to make a larger beam, they use a special glue, it's probably cheaper to buy the right size of lumber.
    – Jasen
    Commented May 12, 2021 at 9:25
  • If you decide to go the glue route, many glue makers say the bond is stronger than the wood itself (and you can find videos of people demonstrating this online). However that's only when it's used properly. So you'd want as straight, square, and smooth an edge as possible (e.g. rip the mating edges on a table saw or with a circular saw first) and then apply sufficient glue, and them clamp the pieces while the glue cures. Of course, buying a 2x8 is probably easier :-)
    – Aaron
    Commented May 12, 2021 at 15:52
  • Sorry to necro an old post, but interested to know how your project worked out. I'm looking to do something similar, though with 2x6's.
    – Droz
    Commented Feb 12 at 0:49

1 Answer 1


A lot depends on what you need these 2x4s to support - how much weight, what kinds of stresses. Supporting a storage area/attic is different from supporting the first floor of a 2-story house. Doing this for a 12' room is different from 50' across a whole house. Lots of variables, and this may well venture into "consult an engineer" territory.

But in theory, yes they could work - metal plates or plywood.

One important thing to keep in mind: a 2x8 is actually 1.5x7.25. a 2x4 is 1.5x3.5. So 2 2x4 is 1.5x7, which is 1/4" shorter. That may or may not matter for your intended use, particularly depending on whether this is replacing or extending existing 2x8s vs. new construction.

  • 1
    So there will be a bunch of 2x4s running perpendicularly across the top of the sistered pieces. The 2x4s that are running perpendicularly across are going to be about 8' long. The largest load that will ever be on it will probably be 300-500 lbs spread out across it's entire length. Thanks for the input - I think sistering them will work for my needs, especially since i'm not going to be consulting an engineer.
    – Brh
    Commented May 10, 2021 at 18:18

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