Building a patio cover, 14 ft projection and 28 ft wide, column at each corner and one in the middle. Shingles over plywood over rafters at 24″. Went to my lumberyard and they called their truss or glu-lam supplier (I don’t remember which) and the response was that I could use either a 5×12 (approx) glu-lam or 2-2×12’s. Obviously the 2×12 will cost less and weigh less so that’s what I’ll do. Question: is there any advantage to gluing the 2×12’s together in addition to nailing?
Replies
Yes. It makes it stronger.
And the preferred adhesive would be...?
Oh, hi -
I'd probably use Liquid Nail consruction adhesive, but I know I'm going to recieve a lot of flack for it.
Anybody else? I'd like to know, too.
I'm a fan of West Systems epoxy. It's pricy, but it's great stuff. I've used it in everything from building a kayak to laminating beams.
Tom
Glue would increase the SIDEWAYS strength up to 4X, in the direction of gravity it does zip for you (so don't bother) unless one of the 2X12s has a big split down the middle.
I disagree. I think a 3" solid has greater streangth than a pair of 2x's sistered. Especially with nails. Not only would I use glue - I would also bolt them togeather with 3 nut, bolt, washers every 16". At the very least, I would use screws rather than nails. But I was wrong once - It could happen again.
Junkhound is right - Glueing them basically does nothing for the strength.
The only advantage I could see was that it might help keep one of them from warping due to changes in the humidity.
A hangover is the wrath of grapes.
I have to agree with Junkhound. In a side load, the nails and glue would provide a shear tie between the 2x12's. But in the vertical direction, there is no such benefit.
Notch the posts deep enough to seat both 2x12's, attach them to each post with two carriage bolts (for stability, not strength) and forget about the adhesive.
I vote for crazy glue!
TDo not try this at home!
I am a trained professional!
I had planned to use Simpson post caps, and set the beam on top of the posts.
The Simpson caps are fine, but not quite as stable as notching the posts. (IMHO, not quite as attractive either.) Bolting the beams to the posts eliminates any chance of the beams rolling over. Unless there are advantages to the Simpson post caps (beyond ease of installation) that I'm not aware of, I'd suggest you reconsider.
If you do use the post caps, I'd still run a couple bolts through the beams. Again, this is for stability and not for strength, so you don't have to go nuts with them.
Just one engineer's opinion.