hey all, this is a first-timer with what must be a fairly simple question for the pros — here’s the set up …
i’m adding a storage attic above a 1-1/2 car garage. a beam will span 16 feet acros the garage to carry the center of the attic floor. i did my homwork and worked with the local building department and got my permit. the plan calls for a built-up beam made from 4 2×12 (s-p-f) with 1/2 plywood (cdx) between the lumber. there will be no splices in the beam, and the ends will sit on a whole world of studs transferring the weight to the sill plate and the foundation.
i’m all set to go, and have all the supplies for the project, and suddenly it hit me — i don’t know exactly how to build a built-up beam. i did some research, but two questions are holding up my hammer right now :
— is it better to bolt or screw through the whole beam or use 16d nails to attach one layer to the next?
— should i glue the layers together?
i’ve seen some conflicting information on these points, and i’d rather not resolve the issue when i hear the attic crashing down on my wife’s car.
thanks for any help anyone can offer.
Edited 2/24/2005 6:03 pm ET by treehouse man
Replies
We use construction adhesive and three 12d or 16d nails at each 16" oc.
What I don't understand is the plywood between. unless you can get plywood 16' long, it won't do any good structurally. maybe stiffin it up a little. Make sure you stagger the joints in the ply by 2' or more so they don't all line up.
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thanks for taking the time. i was surprised by the plywood as well. basically, it's a "because the inspector said so" thing. it didn't cost much, so i didn't fuss.the hammer starts swinging today.
I'd go with bolts and glue. Find the crowns on the 2x12's, and make them all crown up. Clamp the pieces together on the floor and drill for the bolts. Mark them so you get them to line up correctly. Then carry them up one by one. The gluing will go easier if you can assemble it on the flat, and rotate it into its final position.
-- J.S.
A> Welcome
B. What you are describing is not so much a "built up beam" as simply a bunch of parrallel load bearing members. The setup as you describe is simply parallel 2x12s with plywood as thickness spacers as I read your post.
A true "built up beam" is an assembly wherein the extreme fiber tension and compression are carried by "stingers" and the lateral shear by a web of plywood. For a true "built up beam", bolting and gluing are very important. An example is a engineered lumber joists.
If you are simply stacking 4ea 4x12s side by side with plywood spacers, then all ya' gotta do it nail 'em together every so often so they don't rattle - very little strength issue with nailing, etc. assuming there is a common top plate over all 4.
Const. adhesive would be fine to avoid squeaks, but is not needed if I read your description correctely.
edit PS: "Boss Hog" is the resident expert on this type stuff, hopefully he'll see this and respond for you.
Edited 2/24/2005 6:45 pm ET by JUNKHOUND
We usually use steel or lvl's for this. Wonder if anyone considered them? Anyway, I'm kinda in the middle between what junkhound and John Sprung said. I would use construction adhesive but just nail the crap out of it. Crowns up as suggested. Along with Piffin, I questioned the plywood's value here.
Not too big a deal at any rate. Just don't drop it on someone's head or foot.
Dog
i priced lvl and glulam, but they were about twice as much (more to have it delivered) than the site-built beam and didn't save a lot of head height.never looked into steel. i will next time i'm doing something similar.thanks for the help. nails and glue it is. i'm off the garage.
Agree that the plywood seems superfluous here. But it certainly wouldn't hurt. Contruction adhesive as well. But it's extra insurance - might as well spread it on. You may want to build this in place if you're on your own, 'cause you may need help if this mini-monster is on the floor.
Or you could pull the wife's ride into position and stand on the roof.
Is it possible that someone spec'd this beam as a header? Ply spacers are often used in headers to bring 2x stock out to the full stud width.... two 2x and one spacer (1.5 + 1.5 + .5 = 3.5) for 2x4 studs, three 2x and two spacers for 2x6 studs, etc.
Four 2x with three 1/2" ply spacers would be 7 1/2" wide - perfect for those using 2x8 studs! (Now, I've never heard of anyone using 2x8 studs, but that doesn't mean that there isn't provision for it in some header table.)
Can't think of any other reason for the plywood.
BTW, I'm with Junkhound here. You've got 4 parallel beams here. Should be little or no shear between them, so the connection between them is more about stability than strength. Nails alone should be sufficient, but glue won't hurt anything.
Jon
> Four 2x with three 1/2" ply spacers would be 7 1/2" wide - perfect for those using 2x8 studs!
True, but the three spacers would equal another piece of 2x. You could go with five of them, getting the same dimension and a stronger beam because the 2x is one piece. It would be easier to make, since you don't have to rip a lot of ply. Material cost should be pretty much a wash, maybe a few bucks less for the 2x.
As for bolts vs. nails, it probably depends most on what tools you have. I have the big drill and wrenches, which would be easier than hauling out the compressor and nail gun. Plus the big nuts and washers look cool.
-- J.S.
thanks for the help.i submitted the drawings to the building department in my town, so they know this is a beam to span the garage. i wasn't sure why they added the plywood -- perhaps out of header-born habit -- but since it wasn't expensive or difficult, i just went along for the ride. i have a good relationship with the local building office, so i didn't want to strain things for nothing.16ds and glue it is. i'm using makeshift a-frame stands to lift this beam up to its 84 1/2 height -- so if you all hear a crash this weekend, speak kindly of me.thanks again to all. it's great to be a part of something lke this.john
My local rental yard has wheeled masts with a winch - kind of a mini crane - which they let out for about $100/day. Might be money well spent in your case.
AndyAndy Engel
Senior editor, Fine Woodworking magazine
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Well dont just stand there. Go pick it up and drive it over to his house. I'm sure he will give you some beer and food for your effort.