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12-01-2008, 09:27 PM   #1
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## Calculating Weight limits for floor

HI;

I applogize for asking a question so similar to one that was just asked.

I am proboly over thinking this issue, but I figured this is a good thing for me to know.
I am finally getting the garage cleaned out, some of you saw photos of the mess a couple months ago when I built that plywood shelf.

I have been moving stuff / old wood to the garage attic and wondered if the weight is ok for the garage attic.

The garage is attached to the house and is about 20'x22' (22' deep). The Joists are 2x6 16 o.c. In the attic about 6 feet from the front / back edges the joists are cross braced to the rafters. So the open floor space in the attic is about 12 feet wide.

I found this calculator online: http://www.awc.org/calculators/span/...Options#answer

But I am having trouble understanding how to use it properly, and don't know how to take into account the cross bracing. I put 2x6 Spruce pine fir 16o.c. into the calculator on that site and it tells me the maxium span is around 12'. Maybe this is correct, and the cross bracing between the floor joists and the rafters make it ok to be a longer span? If so, then how do I calculate how much weight this attic can bear?

The load proboly isn't that substanial in the attic and it is spread out, but the lumber pile up there might be a couple hundred pounds now.

Thanks in advance for any guidance.

Jamie

12-01-2008, 11:04 PM   #2
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not exactly sure what you are talking about joists connected to rafters. are they attic trusses? is it 45 degree bracing, or are they actual rafters? a couple hundred pounds evenly distributed you can get away with. if there are webs they aren't there for supporting weight on the bottom chord they are distributing the weight from above.

12-01-2008, 11:40 PM   #3
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Quote:
 Originally Posted by chad4290 not exactly sure what you are talking about joists connected to rafters. are they attic trusses? is it 45 degree bracing, or are they actual rafters? a couple hundred pounds evenly distributed you can get away with. if there are webs they aren't there for supporting weight on the bottom chord they are distributing the weight from above.
I can climb up tommrow and get a photo of them if that would help. I belive they are just pieces of plywood around 1/2" thick, I would have to look more closely to say for sure. I've not seen them used before. But they are connected from the 2x6's in the garage ceiling to the rafters. They are not like the factory built attic trusses they sell, it was clearly all built on site.

I think it may be the 45 degree bracing that you mention. Would that be used to help support a long run where there is no bearing wall under it, such as in a garage?

Thanks
Jamie

 12-02-2008, 12:01 AM #4 Member   Join Date: Nov 2008 Location: wisconsin Posts: 39 Rewards Points: 25 ahhh! gussets. get picture. you can probably put some stuff up there i wouldn't get too crazy though. the only way to increase the load capacity would be a larger bottom chord or transferring the load some other way.
12-02-2008, 12:14 AM   #5
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Quote:
 Originally Posted by chad4290 ahhh! gussets. get picture. you can probably put some stuff up there i wouldn't get too crazy though. the only way to increase the load capacity would be a larger bottom chord or transferring the load some other way.
I just searched for the term gussets, and that sounds like what it is.

So the gussets are what are primarly responsiable for giving the attic floor it's capicity, and making the 20+ foot span possiable with 2x6 lumber then correct?

Do you start pushing the capicity of the Rafters that the gussets connect to, or is the capicity of the rafters much higher than any load the gussets could reasonably place on them?

When you mention using a larger bottom chord do you mean something that connects to the rafters again or something more along the lines of a support colum in the garage?

Thanks
Jamie

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