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 2×8 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?
Best Answer
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.