I have a 30x48x14 pole building with bare walls (uninsulated walls) that I want to add a 10x36 loft to stuck in one corner and along the back wall and 9 ft high. My plan is to have a front support beam to the floor about every 12 feet. The back anchored to the large vertical beams that are part of the building. Also a set of steps on the one side to get up and down. My question is; Will 2x6s running front to back spaced 2 ft apart be sufficient for joists or will I need I-Joists? I plan to cover the top with plywood (thicker than osb). I will be storing mostly lighter weight stuff up there but I have alot of stuff to store so the loft will be almost full. See the 1st attached pic for a similar idea to what I'm talking about. Cheers
Lets get some terms straight first.
Vertical members are called columns. The horizontal members are beams and joists span between them.
Next, let's set the live and dead loads. Dead loads are the structure. Live loads are the things you place on the structure.
Typical residential live floor loads are 40#/SF of uniform load for decks, stairs and living areas. You can set this value to anything you want, but this is a good starting point. Let's figure a 50#/SF live load because you will use it for storage and a 15#/SF dead load for the structure weight. This is the combination of the beams and joists and floor sheathing. By the way, use 3/4" T&G plywood floor deck with staggered joints, glued and screwed. And hang your joists from the beams with joist hangers and the proper fasteners.
Now, using a joist calculator like this one, let's size the joists.
http://www.awc.org/codes-standards/calculators-software/spancalc
Let's try 2x8's at 16"o.c. and use a typically available wood species like SPF #2 and better. If you have no finished drywall ceiling below, you can use a deflection limit of L/240. Using the calculator, this will span 11'-1". So it is adequate.
Then the beams. LVL's are what I use for these applications because they will have the least depth, to allow you to maximize headroom both above and below the mezzanine.I will assume that you will have columns to support the beams every 12' for the beams at both the front and back of the mezzanine.
Using this beam table we need to know the load per lineal foot on each beam. The contributing area is 5'x1'x65#/SF. This equals 350#/LF of load on each of the beams.
We need then to decide on the strength of LVL to use. A 1.9E is readily available, so lets use that table.
http://parr.com/PDFs/LP%20LVL%201.9E.pdf
From the table, a 1 3/4x 7 1/4 at L/240 and spanning 12', will support 177#/LF. So doubling these will be adequate. If you prefer to space your columns further apart, say 18', you will need deeper members for your beams. In this case, a pair of 11 1/4" deep LVL's for each beam.
Understand?
Now go price your materials and build it. Show us lots of photos.
Bill
