# 2-ply built-up beam staggered joint location



## WoodPeckerwood

I am building a simple low to the ground deck and need a 20-foot long beam to divide the span from the ledger to the rim. I've checked tables and a doubled 2x8x20' PT Hem/Fir will work fine with posts dividing it into less than 6-ft supported spans. So I'll need either 3 or 4 posts depending on their placement. And placement is dependent on what lengths of lumber I use to make the 2-ply beam. 

I understand that I should locate the butt joints over a post and that I will stagger my joints between the two plys for maximum strength. But beyond those considerations, where is it smart to locate the joints?

Every post is a little more labor, plus connecting hardware and materials, so all things being equal, it would be nice to keep these costs in mind. Minimizing wood waste is on my mind too - so the scenarios I have below are both zero waste. 

Can someone tell me what way to go? Or suggest any other considerations or better options? in both options the first and last spans are cantilevered. The joist spacing is 16" OC.

Option #1 using (4)10' boards
10|10 and 5|10|5 with 3 posts (spans=5'5'5'5') however there are a total of 3 joints in this option vs. option 2. Q:Is minimizing joints critical?

Option #2 using (2)12' and (1)16' boards
12|8 and 4|16 w/4 posts (Spans =4'4'4'4'4')

#3?

Thank you,
Steve


----------



## Donohue Const

Why can't you use 20' 2x8's?

Or am I missing the question


----------



## WoodPeckerwood

> Donohue Const Why can't you use 20' 2x8's?
> 
> Or am I missing the question


This is a city house, tight maneuvering space. Can't get the long boards in. 16' might be pushing it...


----------



## muskoka guy

Codes here say you can put the joints up to 1/10 of the span away from the post. I usually put the front one over the post because it looks better, and the one behind offset to get a good lap for lateral support. A triple I put the third one back over the post. They say this method actually makes the beam stronger due to the cantilever effect. This is how I was taught.


----------



## ScipioAfricanus

Could just use 4x material and butt them over the posts and use a Simpson or equal saddle.

Easiest way I know of.

Andy.


----------



## Golden view

Steve,

Keep it simple. Splice over or nearly over a post. You could just do 10'6/9'6, or as Andy says, don't even worry about lapping the joints. 

Andrew


----------



## WoodPeckerwood

Golden view said:


> Steve,
> 
> Keep it simple. Splice over or nearly over a post. You could just do 10'6/9'6, or as Andy says, don't even worry about lapping the joints.
> 
> Andrew


I was thinking that maybe I wasn't clear in my original post, but your answer makes me think that the answer to my question is "It doesn't matter"

I totally intend to place all splices over posts. Again, my question is: does the location of the splice in the first ply in relation to the location (or locations) of the splice(s) in the other ply, have an effect on the strength of the built up beam? 

Reading my 2 options: it seems like no one is saying #1 is better than #2, even though I am proposing a second splice in one of its plys. 

So am I to conclude that the number of splices and/or the location of the splices in the plys, as long as they are over a post, don't matter ?


----------



## Framer53

Number of spices won't matter if they are over a post.


----------



## muskoka guy

As I stated, I was taught that extending the second ply up to 10 percent of the span between posts actually makes the beam stronger because as the beam tries to sag, the cantilever of the extended ply will resist by creating uplift. This actually helps with lateral strength as well by tying the plies together. I am not a fan of putting all the splices in the same location unless you use some type of metal connection.


----------



## Tinstaafl

muskoka guy said:


> As I stated, I was taught that extending the second ply up to 10 percent of the span between posts actually makes the beam stronger because as the beam tries to sag, the cantilever of the extended ply will resist by creating uplift.


While I see what you're trying to say, in reality nothing creates uplift. IMO any advantage to that would be marginally small. 

But I definitely agree with respect to lateral forces. :thumbsup:


----------



## muskoka guy

Being cantilevered only 10 percent of the span means you have a ten to one cantilever. Any sag in the adjacent span would surely create uplift on the cantilever. To each their own. I have been building beams this way for many years. The main problem is you generally don't want all the joints in one place. This method gives you the ability to move the joints in order to create a lap to nail for lateral support.


----------



## jlsconstruction

Tinstaafl said:


> While I see what you're trying to say, in reality nothing creates uplift. IMO any advantage to that would be marginally small.
> 
> 
> 
> But I definitely agree with respect to lateral forces. :thumbsup:



Take a 16' 2x12 and a chunk of 6x6. Lay the 6x6 on the ground and put the 2x so 12' are on one side. Now you stand on the side with 4' and I'll drive my truck over the other side.


----------



## Tinstaafl

Guess I was being overly technical. Sure, sag in one spot creates lift in another--but overall they cancel each other out. Or something like that...


----------

