# 4x versus double 2x materials



## Vincer (Mar 22, 2011)

Are doubled up 2x lumber stronger than a single 4x piece of lumber, or is it simply a matter of availability?

I mean, should I use doubled 2x's even if I can find 4x material, or is the 4x the stuff to go with (for beams, for example).

And yes, I know doubled up 2xs are 1.5 x 2 = 3 inches thick.

Thanks!

Vince


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## Ron6519 (Mar 28, 2007)

Vincer said:


> Are doubled up 2x lumber stronger than a single 4x piece of lumber, or is it simply a matter of availability?
> 
> I mean, should I use doubled 2x's even if I can find 4x material, or is the 4x the stuff to go with (for beams, for example).
> 
> ...


You use support material based on the load applied. It would be more productive if you just tell us what you're trying to support, rather then getting into a theoretical discussion of which framing member is stronger.
Ron


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## Vincer (Mar 22, 2011)

This was actually a theoretical question, but I DO have a project that I'm starting which it could apply to, but I was going to use 4x8 for a beam anyway.

My specific project (which is outlined in a different thread) is that I am adding some support to a particular part of my dining room floor in anticipation of moving a 180 gallon aquarium to that spot. So 180g x 8.35 lbs/gallon = 1503 lbs. Plus tank ~ 400 lbs + tank furniture ~ 100 lbs + rocks/sand (but rocks would take away from water volume). So around 2000lbs in a 6 foot tank, which would span 4 joists (2x8s at 16 inch centers).

So the current joists (the tank will go perpendicular to them) span 10 feet with one side on the foundation/mudsill and the other side on a beam. 

The tank will be close to the foundation side. There is too many wires and crap to sister the joists without notching so...

I'm going to add an 8 foot 4x8 beam (This is the beam that I'm wondering if doubled 2x8 might subsitute for) at about 4 feet from the foundation (ie the tank would sit withinin the 4 foot span between foundation side and new beam). The beam will be supported by two 4x4 posts that would be positioned about 6 feet apart (part of the beam will overhand), hopefully as close to the corners of the tank as I can figure. The posts will be set on precast piers that will be sitting on 16x16x8 footings. The 6 foot spacing of the posts would actually be adjusted so that the posts sit under joists (or not... is there any benefit?). Douglas Fir is what the posts and beam will be made from. I'll use some shiny simpson connectors to tie it together, more for simple alignment than anything else)

So that's my project in all the gory details (gory to avoid missing something)

My secondary project will be some earthquake retrofit, but I'll bombard the board with questions after I'm done this project.

Vince


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## Gary in WA (Mar 11, 2009)

Yes, 4x is stronger, in each case; http://www.awc.org/pdf/WSDD/C2B.pdf

Gary


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## Daniel Holzman (Mar 10, 2009)

A 4x4 is typically 3.5 inches square, while two 2x4's are 3x3.5 inches. If oriented so the depth is 3.5 inches, the 4x4 is half an inch wider than the pair of 2x4's, and has a moment of inertia about 15 percent greater than two 2x4's.

Since this is a theoretical discussion, let me point out that there is more to this question than simply the dimensions. In order to function as a single beam, the pair of 2x4's need to be properly fastened together, typically using nails, screws or bolts. If they are not fastened together, the actual strength of the 2 boards may be less than twice the strength of a single board, although the actual strength reduction depends on the application.

Another consideration is that a 4x4 is more prone to twisting than a pair of 2x4's properly fastened together, especially if you get green lumber.


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## Gary in WA (Mar 11, 2009)

Then there's plywood; http://www.finehomebuilding.com/how-to/qa/using-plywood-to-build-up-beams.aspx

Gary


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