Pole Barn Loft...framing size questions

[Zebrafive]

I want to build a loft in my pole barn. I would like it to be 30' wide and 12' deep.

My plan is to attach a 2 x? board across the rear wall for 30' to attach joist hangers to. Then on the side wall attaching to the first post will be a 2 x ? laminated beam (built on site) , 30'. It will be supported by adjustable steel post(s). My floor is 6" reinforced concrete. The joists will be 16" on center. They will be mounted on top of the 30' laminted beam, cantilevering past it approx 2 1/2' (my side wall posts are on 9' centers)
Joists will have X bracing at mid point. Loft floor will be 3/4 plywood screwed and glued.

Shelf units would be installed and only items light enough to hand carry would be stored up there.

Now my questions:

1 What size joists for the 12' span? It will cantilever for approx 2 1/2' of the 12'
2 What size board for the joist hangers that will attach to the poles on the rear wall? Should it be two layers ?
3 What size boards for the 30' beam? How many layers? I would not be opposed to more layers if I could drop down a size in lumber.
4 Or would a steel beam be better? Is so what size? How would cost compare to laminted wood?
5 How many adjustable steel posts? Will two on 15' centers be enough? Plus the side wall post for total of three?
6 Any suggestions, ideas?

 

[ustmd]

Have you consulted any of the on line span calculators:

Maximum Span Calculator for Joists & Rafters

There are some variables and trade-offs you can make

 

[KennyG]

In using ustmd's linked calculator, you will want to enter the distance between support points as the span, not the length of your joists. If I understand correctly, this will just be 9 ft 6 in for you. My look at the calculator shows you could get away with 2x6 joists, but you might want to use 2x8 since the cost isn't much more and that would give you lots of margin for storing heavy loads.

A single 2 x ? on the rear wall will be enough. If you are using joist hangers, a second layer won't help. I have often seen the hanger plate one size larger than the joists (e.g. 2x8 joists, 2x10 hanger plate) but it only has to be the same size. I'm old school and for this application probably wouldn't use joist hangers. I would just rest the joists on top of the support plate.

For the beam away from the wall, I would suggest going to a building supply store and have them see if they can get you an engineered beam (truss, i-section, or laminate) rated to span 30 feet. It would be nice to do away with the posts completely. If you can't get a wood beam, you could check out an I-Beam. However, I did a quick back of the envelope calc and I think you would need at least a 8 inch and perhaps a 10 inch I-Beam for this application. That would get it up to the 600 to 750 lb range for a 30 foot beam which could be more than you want to handle.

If you go with posts, I would still recommend buying some type of engineered beams. I would suggest 6x6 timber posts, well braced. One final thought - adding ties from the roof truss down to the spanning beam would stiffen things up considerably. The only caution is that it adds some load to the trusses and pole barn trusses don't always have much margin. However, you might think about some vertical boards that are secured to both the rafter and joist members of the truss and come down to hook to the beam or joist of the new floor.

 

[RxRatedZ71]

I sunk a post in the floor before I poured my concrete and then attached it to the truss overhead for my loft. I used a 2x8 nailed to my back wall and then hung joist hanger on it and set my 2x6 joists on top and then laid my flooring on top of that. Here is one pic showing the post and placement just after I finished my project and before I even got my joists up. I've since put in a second loft on the other side and built some stairs to make it easier to access. I will work on getting a few more pics for you.

http://www.tractorbynet.com/forums/...-my-30x40x12-pole-barn-thread-10-26-10-10.jpg

 

[RxRatedZ71]

Here are a few more pics

 

[Zebrafive]

Thanks for the replies.
The calculator and KennyG confirms 2x6 is minumum for joists. I agree 2x8s is a better option.

My thought on doubling the the rear wall joist hanger was less deflection between each rear wall pole. Might be overkill. A ledger board would save the cost of joist hangers. I think I will go that way.

I am not sure how to use the calulator to size the 30' beam. No posts would be great. I prefer to build it on site out of 2x? lumber. I do not want to tie into the roof truss. My thought on using steel jack posts would be the adjustablitiy if my concrete floor is not perfectly flat/level. I am thinking four 2x8s or 2x10s.

 

[ENG18LT]

Zebra, If you are going to use dimensional lumber for your beam you can not span 30' without posts. To minimize the number of posts you would be better off using a double 12" LVL, as far as the ledger board along the back I would use a single LVL attached with LedgerLock screws. Then set your 2x8x12' floor joists, be sure to use joist hangers along rear ledger. If you go toyour local lumber yard they can help you with sizing and post spacing. Good luck.

 

[MarkV]

I agree that the 30' span is not going to work well using dimensional lumber. Even one post in the middle would make it more doable. The LVL beams would be your best bet by far if you can't bring yourself to set a post. The steel jack posts do not meet code in many areas. This may or may not be a problem for you. Also, many lumber yards that deal in LVL beams have engineer computer models that will calculated the appropriate size needed. The box stores don't offer that service, at least here.

MarkV

 

[rtimgray]

Here's my best guess at this:

If the loft is going to be 12' x 30', this should be 360 sq. ft. Figuring a live load of 40 PSF and a dead load of 10 PSF, we should have a total maximum load of 18,000 lbs. Half of the load (9,000 lbs) will be bearing on the existing wall, so we only need to size your support beam for about 9,000 lbs. Here's a couple of options that I have come up with:

1. With 1 post in the middle, the load on each side will be 4,500 lbs. A single 2x10 will carry about 1145 lbs over 15 ft. A single 2 x 12 will carry about 1695. It looks most likely to got with a beam made of tripled 2x12s would be the best option, although you could probably go with a quadrupled 2 x 10.

2. If you go with steel, with no support in the middle, you will need upward of a 15" x 43 lb I beam or a 10" or 12" wide flange beam (poundage varies). According to the span tables I'm looking at, they will support a whole lot more than 9,000 lbs, but the smaller beams aren't recommended to span 30'. With a post in the middle, you could probably get away with a 6" or 7" I beam or a similar sized wide flange.

3. I don't have any idea what type of engineered lumber beam you would need, but you can ask someone to size a 9,000 lb load over a 30 ft. span and they can probably tell you. I bet it will be a lot better to have a post in middle, no matter what you do.

Good luck and take care.

 

[Army grunt]

I would build a truss (going up) to support your storage aera.Not spend lots of $ers on a carrying beam.I would build the truss in place.Use it to hold your floor,, just my $00.02
Army grunt