Maximum Span for Shed, without supporting posts??

[James]

I am neither a builder or carpenter. I saw a shed today at Home Depot, that measured 16 x 16. It had a loft second story to it for additional storage.

There are no internal supporting posts. The joists were 2 x 10, and spanned the full 16 ft width of the shed.

I was wondering if a person could use 2 x 12s, and span up to 24 feet without supporting posts? I doubt it. Yet, I walked up into the loft 2nd level and jumped on the floor (I weigh 200 lbs), and the floor felt "pretty" solid. Not rock solid , of course. Of course, going to 24 feet would be 8 more feet of span, and could make a big difference

Bottom line, how far can you span with 2 x 10's, and how far with 2 x

12's ? By the way, these joists were 12 inches apart.

Thanks for any comments !!

--James--

[Bob Morrison]

The hard part will be finding 24-foot long 2x12's

[Colbyt]

Rather than me quote what I think, go here and get accurate data:

Colbyt

[Lee K]

Try Wood I-Beams -- Here's a link. Be sure to go to the two PDF files on the linked page to see how they're designed, and a chart of load capacities.

[Louis Boyd]

Use steel trusses. Going 60+ feet is no problem.

[P. Fritz]

Not hard........just expensive ;-) >

[RicodJour]

additional

Someone already posted the Southern Pine span table link. The Canadian Wood Council's Spancalc tool covers other species as well.

R

[Lyle B. Harwood]

? The hard part will be finding 24-foot long 2x12's

They can be had here, but any quantity of them would be a special order item, and they would be priced accordingly.

Unless they were called out specifically, and, therefore, included in the bid, I would look for an alternative, simply because of the money.

[Gerry Atrick]

In my kitchen, my espresso machine is making the GFCI trip. When plugging something else (such as toaster), it doesn't trip. Also, plugging the espresso machine to another GFCI in my kitchen, it doesnt' trip neither. So is it due to the espresso machine or shall I just change the GFCI ?

thanks.

Fred.

[John Gilmer]

BOTH.

The machine is close to the upper limit on "leakage" and the GFCI is on the lower side of the sensitivity threshold.

Is it a good sized machine with a grounding (3 conductor) plug, does it have a polarized plug (one blade wider than the other) or is it "double insulated" using a non-polarized plug (both blades the same width)?

Anyway, if you can, reverse the plug and see if it still trips. If it does, put in a new GFCI (they are relatively cheap). If it still trips, consider junking the machine unless it has a three conductor (grounding) plug.

[RicodJour]

You have an extremely dangerous condition. Plan on ripping out the kitchen and starting over...assuming the kitchen doesn't burst into flames before then.

R

[Larry Caldwell]

Forget dimensional lumber and use TJI framing. Engineered I-joists will do any span you want, cheaper than lumber, and they are lighter and easier to handle.

Larry

[USENET READER]

[v]

Well Bob you are a PE, but do you commonly work with lumber? I recall having bought 24' lumber and didn't think it was a big deal, my understanding was that 24 foot was the longest standard size. Nowadays it is usually finger jointed out of several shorter pieces.

Reply to NG only - this e.mail address goes to a kill file.

[v]

Why do you say ":yet" you walked onto the floor and it was solid? At

16 feet with 2x10s it should be solid. Your Q has to do with anticipated loading, joist spacing, and allowable deflection not just "can I or can't I".

2x10s spanning 16 feet, if on anything like "normal" 16 inch centers (are you sure they are 12" like you said, that would be unusual), is in the ballpark for typical framing for residential loadings, so it SHOULD feel similar to the floor in a typical house. The old carpenter's rule of thumb (for feet and inches) is "half the span (in feet) in inches, plus 2".

Loading goes up exponentially as span increases, so there is MUCH more to it than just "adding 8 feet". In particular, Deflection goes way up - you could have a floor that was strong enough not to collapse, but would sag or bounce quite a bit. (Also, on a short span you can easily have a floor that is very stiff, but that could collapse suddenly from overload.)

Why do you "need" 24 feet like this? 24 feet can be spanned with engineered wood products but very often there is a better way, unless there is a very particular actual NEED for no posts.

Reply to NG only - this e.mail address goes to a kill file.

[Bob Morrison]

Yes. Most of my practice deals with light frame construction.

I didn't say it was impossible, just that it is a little hard to find.

24-foot sticks are not something you can usually just go to the local lumber yard and buy off the shelf.

Not to mention that 24-foot 2x12's will probably not be straight.

Finger jointed lumber has a lower allowable bending stress and should not be used for members subject to flexure. A better choice is engineered lumber from both a cost and quality point of view.

A typical spec might be 1-1/2 x 11-1/4 1.5E LSL as a replacement for

2x12's

[Rick Samuel]

APA has a booklet on rigid frame construction. Benefits are clear span of

48' with 2x10, 24"oc.

[v]

All of this still begs the question - does he "NEED" the 24 foot clearspan for any kind of residential use or storage shed? He said he was looking at sheds - apparently prefabricated ones. If he buys one, if its 24 x 24, they are not going to be able to deliver it.

If its 24 by something less, can it be spanned the shorter way? If its to be two halves to be assembled on site, he is talking about a modular building not a shed.

If he "needs" 24 x 24 clear because he is going to be building an airplane etc., then he has need for a commercial shop building, not a residential shed.

This kind of Q comes up all the time, and among homeowners, I'd estimate that maybe 90% of the time, their use does not actually require the clearspan they think it does, that's just the easiest way out for their limited knowledge.

Reply to NG only - this e.mail address goes to a kill file.

[James]

My use is for a shed that doesn't have internal posts. The REASONS for my stated use are not under consideration. Only the engineering/construction is under consideration here.

Thanks for all of the good replies !!

--James--

[nicksanspam]

If modulus S = bd^2/6 = d^2/4 in^3 for b = 1.5" and bending moment M = Sf = 250d^2 in-lb for fiber stress f = 1000 psi and total load W = 8M/(12L) = 167d^2/L pounds for an L' span, floor loading w = W/(LC) = 167d^2/(L^2C) pounds per square foot (psf) for L' beams on C foot centers.

So 9.25" 16' 2x10s on 1' centers might support w = 167x9.25^2/(16^2x1) = 55.7 psf. On 16" (1.33') centers, w = 42 psf... 11.25" 2x12s with L = 24' make w = 167x11.25^2/(24^2x1.33) = 27.5 psf, with cross-bracing for torsional longitudinal stability.

With a post and beam in the middle to halve the span, 12' 2x10s on

2' centers might support w = 167x9.25^2/(12^2x2) = 50 psf... 2x8s might do w = 167x7.25^2/(12^2x2) = 30 psf.

Nick