How to build a three-ply laminated 2x10 beam and what fasteners to use

by Patrick
(Long Island, NY)

I am building a ground level deck (max 24" of the ground). It is L shaped and will have 2 long beams (27.5' and 31'). The beams will be 3-ply PT SP#2 2x12's using 12' long lumber cut to fit the distances between the supporting posts.

Should I make each beam a continuous beam or make should I make each long beam up out of separate beams the length of each distance between support posts "on center" that but in the middle of the support bracket?

The beams will be top loaded. There will be no joist hangers on the sides. Given the environment, I want to use 316 stainless steel fasteners and preferably screws (structural screws). Which one would you recommend.

What pattern would you recommend for the fasteners? I am in NY state, perhaps the code dictates some of this but I have not been able to find any information in the code.

Editor Comments

Q1: I would recommend a single continuous beam made of staggered dimensional lumber that can span the required distance. I will explain this further in the video below.

Q2: a) I would take some construction adhesive and apply it liberally in between each 2 by 12, screw with a number 10D 3-½" hot zinc screws or spiral nails would be great as a minimum. Longer is even better. But if you are in an environment where salt air or spray is an issue I would use stainless steel 304 screws. If you can get 316 screws that would be even better. And an RSS screw is the finest.

Q2: b) Use a zig-zag pattern and double up on screws at the ends of each board. One above the other separated by about 6-7". Set them at 16 inches on center distances from each other and about 1-2" in from the edge of the board.

Check out this video for more information:

Video Recap

Have you ever had to build a beam, a big triple ply beam that's longer than the lumber that you can buy, let's say 30 feet or so?

How do you do it? Well, we've got a question that came in today from Patrick from Long Island.
And I'm going to explain to you and to Patrick how best to do that.

So, Patrick writes:

"I'm building a ground level deck, maximum 24 inches above the ground, it's L-shaped and it'll have two long beams. One is 27 and a half feet, the other one is 31 feet. The beams will be three-ply pressure-treated SP number two 2 by 12s, using 12-foot long lumber cut to fit the distances between the supporting posts. Question one, should I make each beam a continuous beam, or should I make each beam long enough out of separate beams the length of each distance between the support post and on center with those support posts below the beam?"

I recommend a single continuous beam. It could be done the way you're proposing, but I just would never do that. A lot of problems that could arise from that and it's very easy to build a continuous beam.

So, what you're going to do here if you're working with 12-foot lengths, I would ensure that one of those plies, one of those 2 by 12s is butt joined directly over the central support post. I'm presuming you have at least three given that length.

And then take each subsequent layer of 2 by 12s and offset it right in the middle of the previous one so that the joints are always going to be at least six feet apart. And do that three times.

Take some construction adhesive and apply it liberally in between each 2 by 12, screw with a number 10D hot zinc screws or spiral nails would be great.

They should be hot zinc galvanized for ACQ treated lumber, or use a number 10 wood screw that's at least three inches long, set them at 16 inches on center distances from each other. You can use a zigzag pattern at the ends. Make sure you double it up.

If you do that the beam is going to be obviously quite heavy, you're going to need some help lifting it. But that thing is going to be rock solid.

It will support the structure beautifully, and it's going to give you the most stability and you will enjoy that deck for years to come, Patrick.