Need Framing Help-Freestanding Structure-Deck Type Build

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Old 11-07-13, 09:19 PM
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Need Framing Help-Freestanding Structure-Deck Type Build

I need some guidance on framing a free standing storage loft in my garage that will attach directly to the concrete slab floor.

Use:
Planning to store random stuff up there that a regular garage accumulates over time. Probably won't be extreme, but then again as time passes I'm sure more and more stuff will end up collecting up there, so I want to build it strong enough, but doesn't need to be way over kill.

Sizing:
My plan is to build a structure that is roughly 18' wide, by 8' deep, and will be elevated about 8' in the air.

Construction:
I am planning to build out of:
-2X6's or 2X8's if those are sufficient (More on this later)
-3/4" plywood for the flooring
-4X6 or 6x6 posts
-Concrete to post brackets which wrap the entire bottom of the post for extra durability, with an expansion anchor type setup, or something else that is reasonable.

Live Load and Spans:
Would a live load of 40psf be reasonable in this scenario of storage?

I did the span calculation and it stated max span of a 2X6 is roughly 9' wide give or take using Douglas Fur. This was at a live load of 40psf/dead load at 10psf. If I plan to build it in an "M" structure so the joist/beam runs horizontal with a post on each side and one in the center would this ideally meet the 9' wide span of a 2X6? This would put 9' of span between each of the 3 posts.

Framing:
I've built decks with the standard framing of posts to beam, and then joists resting on top many of times. With this storage loft I was considering using a doubled-up 2X6 end joist (Rim Joist) as the beam on both sides, and hang the 2X6 floor joists directly off of this. The supporting posts would then be located underneath the double end joist. I would build this at 16" on center with metal joist hanger brackets. An example of what I mean can be seen in this picture, but pretent there is no ledger board and the doubled up end joist is acting as the beam which then rest on top of the support post:
Install Front Rim Joist, Beams, and Interior Joists | How to Build a Simple Deck | This Old House
Install Front Rim Joist, Beams, and Interior Joists (continued) | How to Build a Simple Deck | This Old House
Attached is also a picture that represents what I am considering.


Should I be adding diagonal bracing between each support post and the double joist for extra support?

Questions:
-Is a doubled up Rim joist on each end as the beam sufficient? Would this construction be sufficient with the double end joist resting on top of the support beam, but with no actual beam below the joists?
-Would a 2X6 be sufficient in this scenario of weight and span using Douglas Fur, or would you recommend a 2X8 minimum? Seems like the 2X6 would cut it, but wanted some opinions. If necessary to go 2X8 or 2X10 I will, but if I can get away with 2X6 safely I'd rather space the headroom. I'm sure some will say go even bigger, but I don't want to go overkill it since it may not hold a lot of weight when you spread it out over such a large platform, and I also don't want to lose a lot of headroom. But I will go larger if I have to.
-Are 4X6 posts ideal, or would a 6X6 be better? I was thinking maybe using 6X6 for the center posts, and then 4X6 as corner posts. Looking for feedback on what size I should use and if it makes sense to use a thicker post in the center.
-Should I use diagonal supports and if so, what size lumber would be sufficient?
-Is 40psf live load/10psf dead load an ideal calculation for storage or should it be more, and if not, how much should I be calculating?

Please add your experience and input
 
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Old 11-08-13, 09:15 AM
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Lots of eyes but not responses yet. Any tips anyone has to share, even if its just on a portion of the topic would be helpful.
 
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Old 11-08-13, 09:24 AM
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Hi Frank and welcome to the forum. To be honest, I skip really long posts. But even though this isn't my specialty I will try to get back and read through it. Sun is shining right now so limited time .

Bud
 
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Old 11-08-13, 09:34 AM
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Thanks Bud. I went with a long post so I didn't have to ask the questions across a bunch of separate threads with hopes of keeping all the details in one view. Any insight you can share will be great.
 
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Old 11-08-13, 08:00 PM
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My attention span is too short for posts (like yours) that read like a novel. If I view them, it's only cursory, and more often than not I don't respond.

But In your case I'll make an exception--go with a higher design load than 40 PSF for the stuff you'll accumulate up there. And add a 300 Lb. concentrated load, moving it around to maximize shear and bending moment stresses in support members. You want to be prepared for the day your over-weight uncle comes by and helps you move stuff up there.
 
 

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