Floor Joist Beam Spans

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have you considered wood i joists? bring your plan to a lumberyard and they will do the design for you. or google "truss joist macmillan" for example to find simple span tables) i joists are easier to install (lighter), straighter, and can span longer spans. comparably priced to sawn lumber.
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You will need to have it engineered and they will tell you what you need to do. In order to get a permit you will need plans and the plans will need tom have an engineers stamp on them! If it is not required you should still get it done or at least approved by a PE.
That said on This old house they had a span they needed to raise the ceiling on. They cut the joists from 12 to 10" and bolted steel plate cut to size they also had sag and used the edge of the steel to judge when the floor was level using floor jacks to jack the ceiling. I would think with the steel plates on both sides of 2x12's you should be fine. But the snow load will also have an effect as well as the roof pitch! I had a barn built with a 60' clear span. it had 2 with beams bolted together.
Engineered trusses should take care of it for you
More than you ever wanted to know
http://www.alpeng.com/wood_truss_info.html
W
James wrote:

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No, as stated in my original post, I don't want engineered beams. I will use either 2 X 10 or 2 X 12 beams. My questions related to the reading of the Maximum Span Chart for Southern Pine.
To those of you who say it can't be done, it appears that the Chart says otherwise.
My footings will be ok.... don't worry about them. My questions relate to the reading of the Maximum Span Chart for Southern Pine.
Thanks !!
--James--
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James wrote:

OK, sorry i posted earlier about ijoists--i missed your comment about not using engineered lumber. i have worked with 20' SYP 2x12's before. hope you have a good back!
reading the span tables is pretty straightforward, and in spite of what the naysayers say in this thread, at 30 psf live load, you can span 26, yes 26 feet! with a select structural SYP 2x12 at 12"oc(good luck finding that!). that is what the tables at southernpine.com say. the real questions are what is your live load and what is the grade of your lumber.
where i live, duluth minnesota, the city posts what live load you should use for various rooms, attics, storage, etc. on their website. if in doubt, follow the codes, even if you don't have plan review or inspection.
As for grading, I have seen mostly machine stress rated lumber when using structural lumber, but what you get is inconsistent in that there are mixed grades in the same unit. I wouldn't trust home depot however, since they can try to make their prices seem lower by actually supplying a lesser product. if you can go to a real lumberyard, do so. you can probably order select structural SYP if you want, though be prepared to pay for it. a good lumberyard will have someone who knows all about what grades are available.
btw, SYP used to be the common structural lumber, but in the past few years, only doug fir and hem-fir have been available here. -
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Thanks Marson, this is good info and good advice. I am printing it to keep for future reference.
--James--
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Consider a built-up beam at the mid-point ABOVE the joists and then bolt the joists to the beam using angle iron ala . . .
http://www.pbase.com/speedracer/image/2622653 . We've successfully applied this technique on a handful of jobs always, as in this picture, removing a wall after the beam and angle irons are in place. These happened to be 2X6 joists.
--
"New Wave" Dave In Houston



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New Wave Dave wrote:

The OP is talking about a 20' span and a 40 pound live load. That'd be about six or seven hundred pounds load on each connection, so it could be done with a couple or three suitably sized bolts, but stepping over a beam in a space you're using for storage isn't exactly a desirable feature.
To the OP: most people that have objections to engineered joists usually cite fire concerns, but as you're using the space for storage and not habitation that's really not a big issue. So what's the problem with using engineered joists. You might want to price the floor assembly both ways before you make your decision. Lumber prices haven't exactly been going down recently.
R
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On Sun, 09 Jul 2006 02:47:46 GMT, "New Wave Dave"

Nice picture.
I had a 30 year old house with cracks running across the ceiling and did what you did as an addon to stop the sagging.
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James,

A few years back we built a 24'x28' garage. I wanted a completely open lower level, and a fully usable attic (i.e. No truss webs). I never expected to put any real weight in the attic.
I used regular #2 Douglas Fir, 2x12 joists at 16" OC to span the 24' width of the garage. I added solid 2x12 blocking every 8 feet along the span. I used 2x6 rafters at an 8/12 pitch and ended up with about 7 feet of headroom running down the center of the attic.
Yes, with a 24' span the attic floor is a bit bouncy, but not nearly as much as I expected. If you stand in one place and bounce up and down you can feel it, but it's not really detectable in normal walking. Still, I wouldn't want to store an engine block or a library of books up there.
Mostly, we just use the attic to store items like long PVC pipes, empty stereo/TV boxes, holiday decorations, etc. But, I do have a few heavier items up there too.
I could have easily strengthened the floor by doubling up joists or going to 12" spacing.

We used 2x10 douglas fir joists at 16" OC in some parts of our house. That's close to the maximum span for doug fir, but the floors still feel quite solid.

You could use wood I-joists and easily span 24' or more. They're light, straight, and about the same price as 2x12's around here.
Alternatively, you may want to check with a truss company for "attic trusses". These can easily span 24' and still have a usable room in the middle of the attic. I decided against these because of cost, and because I was mostly working alone. It would have been very difficult to install trusses by myself.
Take care,
Anthony
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Thanks for the input Anthony, and your experience is interesting and on point.
From all the input received here, I now have no doubt that I can span 20 feet easily, using #2 southern pine 2 X 12 beams , on 16 inch centers.
I remain curious if anyone can still answer these remaining questions that were in my original post:
--------------------------------------------------
Is #2 visually graded, the most common lumber found in lumber yards ?
Which would be better, 2 x 10 on 12 inch centers or 2 x 12 on 16 inch centers ?? It seems that the latter may be a bit cheaper, but price isn't the primary concern.
What happens if you use a 2 X 12 beam, but put them on 24 inch centers instead of 16 inch?? Do you simply get more deflection, and less load capacity ?
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James wrote:

I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002 / Choose US species and the loads you indicated - you can't span 20' easily or even barely. Your house, your call.
R
James wrote:

I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002 / Choose US species and the loads you indicated - you can't span 20' easily or even barely. Your house, your call.
R
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R:
Well, I must respectfully disagree. In addition to assurances from folks here WHO HAVE DONE IT, as stated in my OP, I have walked on a floor made with 2 X 10's spanning 16 feet. There was no bounce. Surely I can go to 2 X 12's and span 4 more feet.
The chart you pointed to is neat !! Thanks !! It does indicate I would have to use 12 inch centers.
--James--
I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002 / Choose US species and the loads you indicated - you can't span 20' easily or even barely. Your house, your call.
R
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James wrote:

Respectfully disagree with what or whom? The Canadian Wood Council? Let me know what they think of your research - walking on an entirely different floor system and asking people on usenet.
If you want to revise your criteria to justify what you seem set on doing, please feel free. Instead of having 40 PSF as your live load, go with 30 and there won't be a problem. Just be aware that storage can frequently exceed live loads commonly found in a house, and rather quickly.

Right. Or go with a higher grade of wood. Before you count your chickens though, find out if you can get SYP framing lumber where you are for a reasonable price. In my neck of the woods framing lumber is either Hem Fir or Doug Fir. You can get 2x12 in pressure treated lumber but you do NOT want to do that. Besides the greatly increased cost, for no reason, you would have to use different connectors and fasteners and there would be substantially increased shrinkage.
Instead of going through all of that extra effort, why not rethink your objective, realize that indeed it has all been done before, and select a commonly available wood such as Hem Fir Select Structural on 16" centers. Most likely that will be your best alternative.
You should also check out some of the other design tools online at CWC. For example, they have DimensionCalc which will tell you that your 2x12 framing lumber will shrink about 1/4" as it dries. That is area of construction commonly ignored by all too may professional designers and all amateurs.
R
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RicodJour wrote:

That doesn't read correctly. Make that you can get 2x12 SYP in pressure treated...
R
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James wrote:

You seem to rely more on beliefs than code data. You find 2x10 ok for 16 feet - how does that translate into 2x12s ok at 20 feet? He has pointed you to one set of code limits and it shows your ideas are not satisfactory. What you need to do now is check your local code and find out what the requirements are.
Where's Hammurabi when you need him?
Mike
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The longest allowable span I could find on line was 18' 5" -18' 11" using 2 x 12 size of #2 douglas fir 12 nches apart.
Maybe you could inset a foot on each side with posts versus down the middle and span the 2 remaining feet on each end.
RicodJour wrote:

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The longest allowable span I could find on line was 18' 5" -18' 11" using 2 x 12 size of #2 douglas fir 12 nches apart.
Maybe you could inset a foot on each side with posts versus down the middle and span the 2 remaining feet on each end.
RicodJour wrote:

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When I built my large modified-post-and-beam barn/garage I went thru the same gyrations of tables and codes, all of which came up with different numbers.
All approaches use a 'safety factor' between the point of probable failure (read 'broken') and 'working loads'. The factor varies from 4 to 7, and other 'basic' numbers like Modulus Of Rupture (MOR) has different 'opinions' in different publications. So the results vary...
I got the Wood Handbook from the US Forest Service: Huge file at: http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.pdf
and spent hours understanding the formulas etc. It may be worth it to you to do this... as you seem to want to dig in and do your own work based on your own understanding, rather than all the conflicting 'experts'...
I don't have any neat design package, but I'll send you my .123 spreadsheet if you want. I think Excel will open it... Basically you just need the values for: MOR (Modulus of rupture) you want to use, with some safety factor, and the acceptable PSI for the end bearing area (end of beams on supports)...
Here's a look at the raw numbers for hemlock. Get any other wood out of the handbook. ---------------------         Hemlock Density:            50.00    Lb/ft3 Grn    28.00    Lb/ft3 dry         Hemlock Weight (Lb. Per Board Foot)            4.20    green    2.30    dry
        Hemlock Modulus Of Rupture (psi)            6400.00    green    8900.00    dry         Safety factor            4.00    green    6.00    dry     HEMLOCK: Safe Working Loads:                GREEN        DRY         Hemlock Working Stress-Beam            1600.00    psi    1483.33    psi
        Hemlock Parallel (Post end)            950.00    psi    1050.00    psi         Hemlock Perpendicular (Beam Bearing)            360.00    psi    650.00    psi ---------------------------------------------------------------------------------------------------------- (Need a fixed font to see these)
As you can see I used a safety factor of 4 for the green hemlock I was using, and that naturally increases to a factor of 7 when dry. So I was OK with my 6400 pound Yukon driving on the first floor, and it'll have a better safety factor now, 2 years later. And I haven't put much load on the second floor yet....
The nice thing about a spreadsheet is you can try out different size beams and see the resulting MOR numbers and decide on your safety factor.
I just designed and built a 12by12 deck on our Cabin that is about 14 feet above ground. Most codes require 100 Pounds Per Square Foot for a 'Party Deck Load"... California requires 150 PSF in a few towns, as I understand it, after several people were killed in a deck collapse. I used 150 PSF, and had to go to an 8by8 beam on the outer edge because of a 12 foot span. That beam costs $50 here in Vermont. I was able to make tradeoffs on joist size, span and so on. I added a center support beam to keep the joist span to 6 feet, which made a huge difference and allowed 2 by 6 PT joists.
ANYWAY, you might decide to do all this, or not.... and use some tables,
I checked all my barn calculations against tables and they were close....
Have fun!!
Regards, Terry King ...On The Mediterranean in Carthage (Back ...In The Woods In Vermont for the Summer) snipped-for-privacy@terryking.us
a few barn photos at: http://www.terryking.us/photos/barn/2www-barn1-2004 /
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Typically, yes. I request kiln dried lumber when available, but it's rare to find kiln dried around here for anything larger than a 2x8 or so.

Taller joists usually result in a stronger floor.

A much shorter span rating, and you have to use thicker plywood to span the 24" joist spacing.

A 20' wide building with a 2x6 supporting wall at each end would result in a 19'-1" free span. That leaves several options:
Assuming a 30 Live/10 Dead (sleeping areas/attics)
2x10 at 12" OC = 19'-10" span
2x12 at 16" OC = 21'-1" span
Bump the load rating to 40 Live/10 Dead (all rooms)
2x12 at 12" OC = 21'-9" span
On the other hand, if the attic isn't tall enough to walk through and we're talking limited light storage, you could size the "floor" as CEILING joists.
Assuming a 20 Live/10 Dead (Drywall, No rooms, Limited storage)
2x10 at 16" OC = 20'-9" span
2x10 at 12" OC = 23'-11" span
2x12 at 16" OC = 24'-4" span
Obviously, it depends on what James plans to store up there, but I'd probably opt for 2x12's at 16" OC.
Anthony
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In a previous post James wrote...

Use engineered lumber I-joists. 14" TJI 210 @ 16" o/c should be about right.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
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