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I’m in the process of modifying my trusses. The ceiling used to be 8′ high. I’ve turned them into scissor trusses with a 2 in 12 pitch. I used the services of a structural engineer to determine the size and placement of additional webs and gussets. No adhesive was called for. Rather, nearly 1,000 pounds of 1/2″ bolts are strategically placed to counteract the forces upon the connections. If you must use an adhesive, I think Gorilla Glue is the best stuff around today. Expensive, but worth it.
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I'm in the process of modifying my trusses. The ceiling used to be 8' high. I've turned them into scissor trusses with a 2 in 12 pitch. I used the services of a structural engineer to determine the size and placement of additional webs and gussets. No adhesive was called for. Rather, nearly 1,000 pounds of 1/2" bolts are strategically placed to counteract the forces upon the connections. If you must use an adhesive, I think Gorilla Glue is the best stuff around today. Expensive, but worth it.
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I remember a Habitat project where they built dozens of trusses using just gussets and glue, plus a nail or two "to make the inspector happy." It was before I paid attention to these things, but i would not assume it was construction adhesive -- although strong, the stuff may creep in shear. The other, rigid polyurethane glues (gorilla glue is but one version, worth the cost just for picky projects) soun better -- but are too expensive! Epoxy is also a possibility. Even carpenter's glue is quite strong, but not water-resistant enough.
So what's the answer, truss experts? Ron S. designs these things for a living.
This article, which I found with a random Altavista search, describes using liquid nails, gussets, and a jig like the Habitat folks did (notice the nice idiot-proof design of the process, good for hammer-wielding volunteers, and probably good for me too): http://www.vpop.net/%7Eselfrel/articles/fallick49.html
*My project involves a 36' square pole barn. There are 6x6 posts 12' oc in both directions - 16 in all. There are four mid span posts integral with the rafter framed roof. My mechanic works out of an identical structure except his is trussed. His has 2x8 top cords and 2x6 bottom cords with 2x4 webs and 3/8 gussets. His also was an engineered and permited structure having stood for better than 20 years. My rafters are 2x10's and I intend to add 2x8 bottom cords with 2x6 webs and 1/2" gussets, and otherwise, copying his web layout. I just am not sure about the glue to use.Buz
*OK, if you're confident about the engineering. PL premium. Get the big tubes and shop for the best price (maybe $4 per?). Spread over the entire gusset surface, not too thick, and stagger-nail the bejesus out of it without splitting or weakening the wood. If the joints fail, the whole house of cards fails.Some interesting pictures of looks-like-a-truss-but-ain't: http://backwoodshome.com/articles/harris23.html
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I agree with Andrew. PL Premium is the best adhesive you can use for this. I've made lots of them. Make sure you don't skimp on the size of the plywood gussets. Plywood is cheap and makes a very strong connection. I can't name the publication, but I read an article a while ago comparing strength of these connections and plywood was the hands down winner over any other method except solid steel plates bolted through the truss components. Many custom trusses are designed with plywood spec'd as the material to use for a joint.
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Andrew - is "PL Premium" a brand name? "PL" refers to...........?
*Yes, brand name, made by ChemRex, readily available everywhere here, lumberyards, HD, etc. PL, I don't know what it means ... Polyurethane L-something? Probably the same deal as RCD #6 -- a mystery.
*I'll just give my standard speech on building your own trusses:Copying other trusses isn't enough. You still have to make sure you have adequate sized gussets, and specific sizes/quantities of nails. You also have to make sure you have the correct grades of lumber. Just copying sizes of lumber won't work. I would be particularly concerned about doing homemade trusses on something that's 12' O.C. You really need an engineer to evaluate that. Also - I would never rely on glue alone to hold a connection long term.
*Ron - I appreciate your input - particularly as to lumber grades - other than that tho - these two structures are identical and fabing the trusses in place should be pretty straight forward. And - it won't be glue alone holding the gussets - I too would have a problem with that. I'll let you guys know how it turns out.Andrew - thanks for the "PL" info - I'll look for it - probably see it everyday and just don't know it.
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I have a situation where I need to build trusses in place in order to remove mid span posts - it's on a personal project. Anyway - I have an identical truss to copy, from an identical structure but am unsure as to which glue to use under the plywood gussets. Have thought about regular old construction adhesive or maybe Weldwood glue (brand name) ....... any thoughts on this?
Thanks
Buz