Floor Joist Beam Spans

[James]

I plan to build a small garage, 20 feet by 30 feet. I want to be able to span the 20 foot width, so that I don't have to use interior posts.

At first, I was doubtful this could be done, and I have seen comments in these groups that this is not really feasible. Yet, I have closely inspected one of the yard sheds (with loft) at Home Depot, that is 16 feet wide, using 2 x 10 beams on 12 inch centers. It is a yard shed, with a small loft. I went up into the loft area to see what "bounce" the floor had, and it is quite solid, with just a small hint of a bounce (I weigh

215 lbs). So, I have concluded that spanning 16 feet with 2 X 10's is easy, as I have seen it.

But, I know that going from 16 ft to 20 ft wide is 4 feet more of span and is 25 % more of a span. I am a novice, but I try to find answers for myself first. Somehow, I got a span table for Southern Pine lumber. The title of the chart is

Maximum Spans: Souther Pine joists and rafters .

This is the full name.

The chart also says: 40 lbs psf live load/ 10 lbs psf dead load/

240 deflection / cd = 1.15

I plan to use the loft only for very light storage, but these "load" figures seem very low to me. But, once again, I have "felt" what a 16 ft span using 2 x 10's feels like, and it seems very sturdy to me.

From the chart, it appears that a # 2 visually graded (is that what you "usually" find in lumber yards and the big box stores??) 2 X 10 beam on 12 inch centers will span 19 ft, 11 inches.

A 2 x 12 beam on 16 inch centers will span 20 ft, 2 inches.

-----------------------

Questions: First, am I on the right track ? Does the chart seem to apply to my needs and plans? I could email the chart (pdf format) to anyone who wanted to look, I don't think I should post an attachment here on a news group.

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 ?

I know I could use an engineered beam, but I don't want that.

Thanks for any tips, experience, and advice !!!!

--James--

[Glenn]

2 x 10 spanning 20 foot will sag under their own weight. 2 x 12 would work if the load is really light. You want nothing in the way of parking. That is reasonable but would it be possible to have a drop from the ridge every 4 feet with a stiffback? 2 x 8's would work that way quite well. Even push the envelope with proper dropping braces using 2 x 6's as that's only a 10 foot span less the cantilevering effect in the center of continuous joists. Certainly, the latter would hold a bigger load than the 2 x 12's..

Example: I have a garage that is 24 feet wide. I have no ceiling in it except 2 x 6 joists (cross ties) every 4 feet. They are nailed heavily to 2 x 6 rafters on 5 and 12 pitch. I have a 1 x 4 drop nailed onto the rafter at the ridge and dropping down and nailed onto the joists. To not split the 1'x, I stapled them with multiple 2-1/2"staples. I have a 6 x 6 - 5 feet long laying across 2 of them and think nothing of pulling a 8 cylinder engine on them. I wouldn't even think of doing that even spanning across four 2 x 12's.

[MDT at Paragon Home Inspection]

As a theoretical matter, to maximize span for a given floor thickness the entire floor structure should be designed as an engineered structure, with sub-flooring, fasteners schedules, adhesives, dimensional and engineered members, etc. specified together. By adjusting these variables a structural engineer can spec designs for residential floor spans of 3O'+ using readily available components.

As *practical matter*, my first question would be: "What does the local building department require?". Your question may be answered right there, and there might be some surprises - for example since you now have a load bearing second floor, you may find substantial footings are required below the exterior walls.

My second question, if you are permitted to build as you please, would be "What is a reasonable design criteria considering the loads that might reasonably be placed on the floor by subsequent owners?"- keeping in mind that they may stack old newspapers up there...

Once you know those numbers (load sq/ft and allowable deflection), as specified by local code or derived by common sense, you are ready to start thinking about materials and techniques.

Michael Thomas Paragon Home Inspection, LLC mdtATparagoninspectsDOTcom

[James]

Thanks Glenn, very interesting. No, I want to use straight horizontal beam joists, and had questions about a spannig chart for Southern Pine wood.

--James--

[James]

This place is so remote, they have never heard of a building inspector. And yes, I will have 36 inch depth, 12 inch wide poured footings around the perimeter of the garage.

Thanks !!

--James--

[wayne]

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

[marson]

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.

[Michael Daly]

Then build anything you want and watch and see if it collapses. However, I don't know of any place in the western world where building codes don't apply. BTW - your insurance agent may have something to say about this, too.

Which means nothing without knowing what the soil is like.

BTW 2x10 would not be legal for that kind of span as a _floor_ where I live. Without checking, I don't think 2x12 would work either - 2x14 sounds about right.

Mike

[James]

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--

[MDT at Paragon Home Inspection]

Sounds like you are headed in the right direction: thinking of this as a serious structure, not just an up-sized "garage" on a pad + loft space. I'm not an engineer, and I try hard not to play one the net, but I *do* know that some of the scariest things I've seen in new construction in my area result from architects and/or builders who land jobs to build 'McMansons" and just assume that the materials and techniques that worked for a living room with a 22' clear span can be "up-sized" to work at 26' even 30 or even 35' - there is a 4M dollar house not too far from me where the second contractor on the project worked with an engineering firm for six months to stabilize such a structure, essentially erecting a permanent structural steel frame inside the existing footprint to literally keep the building from collapsing.

Michael Thomas Paragon Home Inspection, LLC Chicago, IL mdtATparagoninspectsDOTcom

[MDT at Paragon Home Inspection]

spannig chart for Southern Pine wood.

See the first table here, for a 20' span garage w/ floor above:

Michael Thomas Paragon Home Inspections, LLC Chicago, IL mdtATpragoninspectsDOTcom

[James]

Michael, thanks for the link, that is very helpful !! From that page, it pretty well confirms for me that the 2 x 12 on 16 inch centers is precisely what would work in my planned structure .

Thanks again !!!!

--James--

[marson]

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.

-

[James]

Thanks Marson, this is good info and good advice. I am printing it to keep for future reference.

--James--

[New Wave Dave]

Consider a built-up beam at the mid-point ABOVE the joists and then bolt the joists to the beam using angle iron ala . . .

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.

[Steve Barker LT]

try Cedar county Missouri. No permits required for anything except a septic system.

[RicodJour]

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

[Michael Daly]

Not requiring a permit and not having a building code are two different things.

Mike

[Steve Barker LT]

Ok, then. If there's no permit required, and therefore no inspection, where does the code come into play?

[crhras]

Code is the law and permits and inspections help the compliance and enforcement of that law. There are many situations where laws are not enforced yet it is still in your best interests to comply with them.

April 15th comes to mind.