Can I use 4x4's for deck support beams?

Question

I am building a deck and have used 4x4's as posts cemented into the ground. Now that I'm to the beam-stage, I'm wondering why you can't use 4x4's as the beams rather than use multiple 2x stock with plywood spacers (or some other combination). Is there some weakness or other issue caused by using 4x4's instead? Seems logical to use since they are same size.

Answer 1

a 4x4 is not going to be as strong as two 2x4 nail together I'd use 2x8 for the beam and the joists....depends on how big the deck is

Answer 2

the strength of the beams  is not in the thickness of the wood but rather the width. one 2x6 is stronger on end then a 4x4. but has a lower crushing strength. the 4x4 will hold more weight and be less likely to buckle when stood on end then the 2x6. and i think the 2x6 or 2x8s will be cheaper.

Answer 3

The beams need to be strong enough to carry the floor joist.

A 4" x 4" is no stronger than a 2" x4" on edge. It could be a 10" x 4" but if you lay in the 4" way it's still not strong enough. Now stand it up so the 10" way is up and down, and it's more than enough.

Don't allow your floor joist to span more than their height.

Example a 2" x8" deck joist should not span more than 8'.

And your center floor beam ( one that floor joist rest on in the middle of the deck) should be double layer (no plywood please) up the next size from your floor joist.

If floor joist are 2" x8" your center floor beam should be doubled 2" x10"

Answer 4

Lowes has a deck designer feature on their site.  Do  web search for "lowes deck designer".  It offers some good suggestions.  I used it to get ideas for a 8'x32' deck I built a couple of years ago.