[HandyJOAT]

Hello all. I am building a deck and was wondering about something. My deck is 46' long and 12' from the house, with a 10'x12' bump out. It is attached to the house with a ledger and is 8' off the ground. I am using triple 2x12's as my beam. So here is my question, when I butt the 2x12's together as I nail them do the butts have to be supported by the 6x6 post. Or can the butts be between the posts? I will be gluing and nailing with 3.5" nails. TIA

 

[Daniel Holzman]

As long as you use an adequate nail pattern, there is no need to support the beams at the joints. Since you are using a triple beam, best to stagger the joints. Your local building inspector should be able to tell you what an acceptable nailing pattern is, if they don't know, you can use the Prescriptive Residential Deck Guide available here http://www.awc.org/codes-standards/publications/dca6. The glue is OK, but is not necessary, you only need to develop adequate shear, and the right nail pattern will do this.

 

[Mingledtrash]

As long as you use an adequate nail pattern, there is no need to support the beams at the joints. Since you are using a triple beam, best to stagger the joints. Your local building inspector should be able to tell you what an acceptable nailing pattern is, if they don't know, you can use the Prescriptive Residential Deck Guide available here http://www.awc.org/codes-standards/publications/dca6. The glue is OK, but is not necessary, you only need to develop adequate shear, and the right nail pattern will do this.

Hi i am a professional rough carpenter. Saying it is ok to have a joint in the center of a beam is bad advice. Unless you have a Structural engineer sign off and give you a stamp you will fail any inspection. it is generally just a bad idea. that being said it is possible to have a joint if the beam is oversized for the loading and deflection again you would need a structural engineer to determine how much bigger the beam would need to be.
Do not do this unless approved and stamped by a structural engineer.

 

[ront02769]

As noted, you need to contact the locals. some codes allow for the joints not to fall over the posts as long as they are within six inches of one....others different. Simplest to meet all is just to put the joints over posts and be done with it. Ron

 

[cortell]

Mr Holzman is among the wisest contributors to this forum, and I would not dismiss his opinion that quickly. That said, I've always thought that if a splice does NOT fall over a support, you should consider the two butting members as not contributing to the beam's strength, but instead acting to stiffen the beam (reduce bounce). So, yes, my amateur advice would be the same: do it only if two plies satisfies prescriptive code.

I found this FHB article that provides an in-depth opinion from an engineer. It, too, discourages splices not over beams, unless engineered.

http://www.finehomebuilding.com/how-to/qa/joints-in-built-up-beams.aspx

Hi i am a professional rough carpenter. Saying it is ok to have a joint in the center of a beam is bad advice.

 

[Daniel Holzman]

The Prescriptive Residential Deck Construction Guide shows the required fastener pattern in Figure 4, and there is a note that states that splices must occur over a post. So if your jurisdiction uses the Prescriptive Guide, you are required to put your splices over a post, unless you get the beam engineered, as others have noted.

I was trying to point out in my original post that a multiple element beam will behave exactly the same way structurally as a solid beam of the same dimension, so long as the fastening pattern develops adequate horizontal shear. If there is adequate horizontal shear, then the multiple element beam is effectively one solid piece, and there are no "splices" from a structural standpoint, so you can put the posts anywhere. After rereading the code, it is clear that the fastening pattern shown in Figure 3 is NOT designed to develop the required horizontal shear to make the multiple elements act as a single beam, hence the requirement to put the splices above a post.

Conclusion: Unless you achieve the required horizontal shear, and prove it with calculations for the selected fastener pattern, you need to put the splices over a post. My apologies for any confusion I may have created.

 

[Mingledtrash]

Thanks for clearing things up Daniel I did not mean to dismiss you offhand. I only commented because i have worked with people on there own projects on weekends and know you have to be careful what you say to a layperson. Some times the only part they hear is the "its ok to do this" but the "as long as you make sure" part of the conversation goes in one ear and out the other. i am not saying it would happen here only that sometimes it does.