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jusolson 12-02-2009 11:43 PM

roof truss explaination
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Hi guys. I've got a few questions about my roof trusses that i've ordered ( and installed already) for my garage. I attached a pic of the spec sheet that came from the company. I don't know alot about live load/ dead load/ ect... As you can see I had them design a storage area in the middle. I would mainly like to know how much weight I could confidently store on these things. I'm also trying to consider the weight of the ceiling and a floor in the storage area. So far I'm thinking of using 5/8 cdx plywood as a floor. I don't want to use sheetrock for a ceiling for weight, something much lighter. I guess if anybody can put some of the specs in better english it would help. Also, there isn't anything about lateral bracing on the plans. I would feel much better with some additional 2x4's holding them together. What configuration would be best? And then I am curious about how one might go about insulating the attic. So far I'm thinking about using 2x6 batts under the storage area and then pile up blown in insulation on each side. Thanks for taking a look and for your opinions!

DangerMouse 12-03-2009 05:08 AM

how much space between trusses? 12"? 16"? 24"? is the garage to be heated?


jogr 12-03-2009 09:45 AM

Read the drawing carefully.

In box at bottom right t says your bottom chord is rated at 10 psf dead load so 5/8" drywall and plywood floor on top would be no problem. Check out the weight of a 4x8 plywood or drywall sheet and divide by it's area (32 ft) and you'll see that combined they are well below 10 pounds per square foot. The only other dead load on the bottom chord (b.c.) is the chord itself which combined with the drywall and plywood would also be well below 10 psf.

It also says 0 psf live load on bottom chord in the same box. But on upper left it says the bottom chord passsed check for 20 psf live load in areas 42" high x 24" wide. So that's where you can store things and what the weight limit is.

Your plan also says (top left) that continuous lateral bracing (CLB) is required at 24"oc across the collar ties which would typically be 2x4s at least 12' long and overlapping at least one bay. But it also says a rigid ceiling (drywall or plywood across the collar ties) can serve that purpose.

There is also a shear warning on the top right that I can't read but it says something about special positioning.

In addition to the bracing on the drawing you might need other bracing not shown. Your truss manufacturer should have given you permanent bracing requirements. Typically the bottom chord requires CLB or rigid ceiling and the top chord requires plywood sheeting (which you are going to do) but the upright web chords should typically also have both CLB as well as diagonal bracing. The diagonal bracing is very important. Call the truss manufacturer and ask for bracing requirements.

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