How much weight can my garage attic support?

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  #1  
Old 04-15-12, 06:32 AM
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How much weight can my garage attic support?

Hello!

Just moved into a different home and I'd like to use the space in the garage attic for some geneeral storage such as totes of clothes and shoes, seasonal items, etc.. I just finished laying some 1/2" thick plywood across the trusses, but as I was up there, I noticed the truss system is held together only by thoses spiked plates and I got a little worried that it wouldnt be safe to put storage up there.

Its a typical 2x4 truss system; 24" on center and from floor to peak is only 3.5'. The span I would like to utilize is just over 7' and the ceiling underneath is finished with drywall. How in the world can I determine 1) if its safe to store stuff up there and 2) how much stuff I can store up there? So far, its held me (250 lbs) the six 8x4 plywood boards, an existing roll of insulation and a roll of leftover carpet. Its doing ok, I just want to make sure I dont over-do it.

Thanks
 
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Old 04-15-12, 09:12 AM
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Truss systems aren't meant to hold much up but the sheetrock and insulation applied. They are not intended for storage. What is the span of the trusses from end to end without support? Generally you may get away with storing light stuff, like Christmas trees, but it will graduate to heavier items, guaranteed, until there is a failure. Then your only recourse would be to post and beam the center of the garage. So do it with caution.
 
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Old 04-15-12, 11:00 AM
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I believe the truss is a 24' span without anything supporting them.

Is there anything I can do (that doesnt break the bank) to make it suitable for storing things other than putting posts from garage floor to ceiling which would make the garage unsiutable for a car.
 
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Old 04-15-12, 12:03 PM
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You can only store stuff up there if the truss was designed for it. They are called "attic trusses". You will be able to tell if you have them because there is a large open rectangle in the truss. If you have diagonal webbing going through the middle, then you don't have one. Something like this: Image Detail for - http://peaktruss.com/images/atticTruss.jpg

You also want to be careful about attaching lumber to your trusses. They are designed to carry loads in a specific way and adding anything to them can change that. I think the plywood you laid down on the bottom is ok, but only an engineer can tell you for sure.
 
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Old 04-15-12, 12:07 PM
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This might be the best idea. My patio was made about the with 24 oc. It had a heavy tarp, that I would take down for the winter. But started get old, and I wanted a real roof. The way it was laid out, I couldn't go with 2X6 16 oc. So I went with 2X4 12 oc. 3/8 plywood, 20 lb felt, and shingles. I would get a foot or so of snow, and rake it off. But I had to go away on business, and by the time I got back there was over three feet of wet snow. I got it off first thing the next day, what a job, that is a lot of snow.
 
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Old 04-15-12, 12:14 PM
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Most trusses are designed for only 10 lbs psf live load for storage, unless they are attic trusses like Drooplug mentioned. You've added about 300 lbs already when you put 6 sheets of plywood up there. As Larry said, don't overdo it.

A person might think that going by the 10 lbs psf limit, that he could safely put 270 lbs on a 4x8 sheet of plywood (270 + 50 lb sheet of plywood = 320 lbs, or 10 lbs/sf.) If you weigh 250, that means you could safely have 20 lbs up there with you on one sheet of plywood.
 
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Old 04-15-12, 12:58 PM
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He might still be overdoing it because his 250lbs is a point load rather than a distributed load;the plywood would not distribute the load to more than perhaps a couple of trusses.
 
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Old 04-15-12, 01:04 PM
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Good point tony, that's where I was going with the "a person might think" sentence but I never quite finished the thought. A person IS a point load. Unless you chop him up and spread him evenly on the attic floor... LOL
 
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Old 04-15-12, 03:10 PM
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I hope the OP doesn't cut the struts out to give more space!. This reminds me of a recent case here in the uk where a social housing tenant decided to make a loft conversion in his roof space. He took a saw to all the struts (thinking they were unnecessary) put chipboard on the ceiling joists and thereby made himself a new bedroom.
Soon after, the roof sagged (naturally, under the weight of several tons of tiling) and the adjoining tenant called the authorities. As soon as the building inspector put his head through the trap door and saw the danger, he immediately ordered the evacuation of the house. At the subsequent trial for criminal damage, the judge said the tenant was "not an evil man, but a very stupid one"; he was sentenced to a community service order. This didn't help the landlords of course, who had to spend on a new roof. Moral of the story?; no builder puts unnecessary timber in a roof!
 
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Old 04-16-12, 03:43 PM
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Thanks for all the information. Im not sure what kind of trusses I have, but I am pretty sure I dont have a rectangle up there; I beleive its more of a triangle than anything.

It sounds like its better to not use it for heavy storage (for sure), but is there a way to make it so I can? Can I do something to the truss to make it more like an "attic truss"?
 
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Old 04-16-12, 05:44 PM
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Thanks for all the information. Im not sure what kind of trusses I have, but I am pretty sure I dont have a rectangle up there; I beleive its more of a triangle than anything.

It sounds like its better to not use it for heavy storage (for sure), but is there a way to make it so I can? Can I do something to the truss to make it more like an "attic truss"?
 
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Old 04-16-12, 07:01 PM
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You could put a beam down the middle and install posts on both ends cutting the truss span in half. You would still need an engineer to design this to see if it is even an option.
 
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Old 04-17-12, 04:15 AM
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You need to have an engineer tell you what you can do.
 
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Old 04-17-12, 05:34 AM
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You mentioned in your original post that you only had 3.5ft clearance at the centre. This will not, therefore, be an attic truss, as those are intended to provide space for living accomodation. Yours will be a simple truss with diagonal struts joined together with gang-nail plates. These systems are not designed to carry more than nominal ceiling loading eg bulky but light items.
Several posters have suggested getting an engineer in to advise on how to provide extra support. This might not be practical as the trusses are computer-designed, and the engineer won't know the strength of the fixings.
With traditional roofs/ceilings, you will see them bend under increasingly heavy loads long before they fail. On the other hand, trusss are light but rigid and they can collapse under excess load without warning. People tend to pile stuff up there and when the trusses look fine and don't bend, they think its OK to keep putting stuff up. Your best course is to be sensible and not overdo it.
 
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Old 04-17-12, 08:00 AM
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And don't do like my friend did in his new garage......drill a million holes in the trusses to run the electrical wires.

His dad looked up and said, "I don't think you're supposed to do that."
 
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