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Reinforcing garage attic trusses for storage area

Reinforcing garage attic trusses for storage area

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Old 02-01-17, 09:18 AM
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Reinforcing garage attic trusses for storage area

I have an attic above my two-car garage that I have been using as a storage area. Originally I just put loose boards down over the horizontal 2x4 base of the trusses. To make the area more useable and secure, now I want to put in 5/8" plywood over those 2x4s.

I know that the trusses are strong but am concerned about hundreds of pounds of plywood and storage items causing them to sag over time. Is it necessary to reinforce the trusses before putting down the plywood? If so, how should I do this? I was thinking of adding a vertical 3 to 4 foot 2x4 between the rafter (angled upper piece of the truss) and the base (horizontal bottom piece of the truss) on each side, as shown in the attached diagram.

Pictures of the attic area and a drawing of what each truss looks like and the reinforcement I am considering are attached. Thanks for your help.
 
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Old 02-01-17, 09:54 AM
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Unless those 2x4s are supported all the way to the ground, I don't see them helping.
 
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Old 02-01-17, 10:09 AM
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Agree, the 2x4's you want to add will only cause the roof truss (the 45 deg ones) to sag at the point of contact. You would be better off laminating a new set of 2x4 or 2x6 beams from either end and placing the plywood on top of that. This assumes that you can gain access to the end caps for support but you would have to limit the overall weight on the structure.
 
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Old 02-01-17, 10:28 AM
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It pretty common for people to think that their "reinforcement" of a truss will somehow make it better or stronger. In reality, you can do more harm than good by altering a truss and completely changing the stress and tension points on the truss. My best advice would be to not alter the truss at all... your framing proposal is of no help. Don't use 5/8" plywood as it only adds more weight... reducing the amount you can safely store. Use 3/8" or 1/2" plywood if you have to lay something down, and lay it perpendicular to the truss chords.

Use common sense and do not overload the trusses. The bottom chord CAN be overloaded, it is already in tension, meaning the tendency will be for it to pull apart (or break) at the point of stress or where it is fastened with a mending plate, whichever is greater. Your trusses were engineered to only hold x amount of weight. Generally that is only meant to be it's own weight, the weight of the building materials that are already on it (drywall, sheathing, roofing) plus potential snow load, wind load and live load. The live load is your "storage" and it is a limited amount in that equation... generally it is anywhere from 5-10 lbs per sq ft, but we can't say for sure.

How much your trusses are rated to hold is something only the mfg knows, or if you can find a tag or stamp, that might help.

So without knowing for sure... don't concentrate loads, and don't put more up there than 5-10lbs per sq ft. If spread evenly, a 25x20 garage "could" support 2500 lbs @ 5lbs/sf. But don't start by putting 500 lbs of plywood up there.
 
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