I have to replace a 20 ft beam that spans from gable end to gable end of a small barn. I want to make the beam. I am going to use 2by 10s and 3/4 plywood glued and nailed between them. Do the 2by 10s have to b 20 20 footers or can I piece them and stagger the joints?

Why are you replacing the beam? Have you fixed the cause of deterioration? Was the old beam constructed the same way? Did it do the job before it deteriorated? What kind of load does this beam have to support? Will an inspector see it?

The beam you describe will not support much of a load. It will support itself, and maybe a jolly jumper. :) Even if you used full-length 2x10s the beam could not support much more. The building code probably specifies 4 2x12s for that span. (just a guess)

Assuming you are satisfied the beam you describe will do the job, you can construct a new beam with 8' and 12' 2x10s. This will stagger the joints by 4" You can keep the joints in the plywood filler 2" away from the joints in the 2x10s. Use dry wood, the best quality you can afford. Make sure all the butt joints are tight. Use construction adhesive, and lots of #8x3 deck screws screwed from both sides. Use clamps so that the assembly is tight before driving the screws. If the joints are open, the screws may not draw the assembly tight.

If you could put a post under the middle of the beam, that would be better.

Dale posted this question twice, the other one was tagged onto another subject Dale had. I answered there and said not to splice the 2x10. You can spice 2x lumber in a truss but I do not think you can do this in a engineered beam. If we have any engineers who can answer this I would appreciate their help. Most of us here are not qualified to tell you tp splice a beam. I imagine you need a permit so ask your building inspector what he thinks.

Agreed. I posted this because he is replacing an existing beam. I have edited my response.