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Old 10-29-2011, 12:38 PM   #1
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decking an unfinished garage attic?


Hello all,

I'm pretty handy with carpentry and construction, but am not a professional so I wanted to get some advice.

I have an unfinished, detached garage and I would like to deck the attic, so I can use it as a light storage area. The garage is a 35yr old sloppy build, and was never built with an attic in mind. The building is about 21.5' x 22.5'. The wall studs and roof joists are 20" on center. There are 2x6's bridging the structure, spaced 40" on center and spanning the entire 21' portion of the garage overhead, I assume just for stability, not for to support load. The roof is very shallow grade, at about 15-20deg.

The issue is over the years the 2x6's overhead have become a place to store boards and junk. And as you all might expect, with a 20+ span for 2x6's, even without load, they are sagging like soggy paper. A few of them I've jacked up braced to the roof joists with 2x4's.

Also, a 12' addition was added onto the back of the garage without touching the main structure, just scabbed on.

What I would like to do is replace these 2x6 spans with something I can at least put weight on, and deck out. I'd like to be able to carry and store junk up there without the whole thing caving in. I don't intend to ever use it as a living quarters, just attic storage. We also live outside of major cities, so codes and permit requirements are pretty much nil (I've checked), especially since this is not an inhabited structure.

Any ideas out there for what I should do, or what you guys see done out there? I'm looking for economical solutions. I was considering joining 12' 2x6's, spaced at 16" centers, and running supports down from the roof joists along the middle, but I hate putting the load support on the roof. My only other thought is I'd have to run a long 22' load bearing bean across the center and attach 12' joists perpendicular to that, but a beam of that length would be pretty pricey.

Again, this is only for light storage, and occasional person climbing around.

Any thoughts are welcome!

Thanks!
Adam

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Old 10-29-2011, 07:39 PM   #2
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decking an unfinished garage attic?


You could span it with engineered lumber.

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Old 10-29-2011, 09:18 PM   #3
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decking an unfinished garage attic?


Depending on the size of your rafters hanging an additional load on them may not be possible. One of the safest, easiest and cheapest solutions would be to run a beam front to back with three or four posts to support the midpoint of the 2x6s.
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Old 10-30-2011, 09:58 AM   #4
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decking an unfinished garage attic?


Thanks guys.

Ron do you have any suggestions for engineered wood? I've never dealt with the stuff.

I'm definitely open to a single beam, I'm just not sure the best way, or what kind of beam. Supporting with posts is not an option since this is a garage, so the entire space below needs to be open. The roof rafters are just 2x6's, 20" on center, which is topped with spaced 1x4's and decked with ply and shingles.

Since this won't be an inhabited attic, I'm wondering if I could do some minimal spec beam across the center, and add supports from that to the roof instead of posts--not for primary support, just to prevent sag. Any thoughts?

Adam
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Old 10-30-2011, 10:17 AM   #5
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decking an unfinished garage attic?


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Originally Posted by heli0s View Post
Thanks guys.

Ron do you have any suggestions for engineered wood? I've never dealt with the stuff.

I'm definitely open to a single beam, I'm just not sure the best way, or what kind of beam. Supporting with posts is not an option since this is a garage, so the entire space below needs to be open. The roof rafters are just 2x6's, 20" on center, which is topped with spaced 1x4's and decked with ply and shingles.

Since this won't be an inhabited attic, I'm wondering if I could do some minimal spec beam across the center, and add supports from that to the roof instead of posts--not for primary support, just to prevent sag. Any thoughts?

Adam
You can do it 2 ways. The easiest would be a single beam dividing the span. You'll need footings on either end to support it.
Go to your local lumberyard with all the info. Call them up first to see what you need. They should be able to spec out a beam for the space.
If they can't, you'll need to contact an engineer who can.
The other option is to add engineered joists across the span to support the expected load.
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Old 10-30-2011, 11:46 AM   #6
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decking an unfinished garage attic?


Definitely go with the single beam and don't attach to the rafters. There are a lot of options for the beam, you could easily use steel or wood. You will definitely need to have it engineered to ensure safety.
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Old 10-30-2011, 12:59 PM   #7
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decking an unfinished garage attic?


By code you get away with 2x10s @ 24" OC. Using #2 DF.
That is assuming a dead load of 10 PSF and a live load of 20 PSF for limited storage. (assuming your are in an IRC 2010 area).

Why do I give away this info for free?

Andy.
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Old 11-01-2011, 07:33 PM   #8
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decking an unfinished garage attic?


Lol, Andy, you got me to chuckle on the "IRC 2010 area" as well. http://publicecodes.citation.com/icod/irc/index.htm

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Old 11-01-2011, 07:52 PM   #9
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decking an unfinished garage attic?


Oops, my bad Gary, we are on the CRC 2010 here in California based on the IRC 2009.

I get confused. (which is my normal state)

Andy.

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