What size joists?

[tom-ky]

We have a enclosed 12 foot lean too on our 30 x 40 pole barn/garage. We are planning on making a enclosed area in the lean too and wall off between it and the garage. It will be insulated with a ceiling. So there will be a few open feet that I planned on flooring for storage. What would you suggest for joists? I thought 2 x 8's. I hope I made my question clear.

 

[bczygan]

How big will the floor be and what will the span of the joists be?

What will be on them?

Bill

 

[bruincounselor]

I'm guessing you are asking about a 12' span on 16" centers? What load do you intend it to support?
Linky:
http://http://www.awc.org/codes-standards/calculators-software/spancalc

 

[tom-ky]

How big will the floor be and what will the span of the joists be?

What will be on them?

Bill

Probably only go 6-8 feet floor as I will lose usable height.
Planning on 16" centers.

Just general storage, maybe some parts but nothing really heavy planned but want to be safe.

 

[tom-ky]

I'm guessing you are asking about a 12' span on 16" centers? What load do you intend it to support?
Linky:
http://www.awc.org/codes-standards/calculators-software/spancalc

Your link doesn't work for me.
We just plan on using it for general storage, not really too sure but want to be safe.

 

[bruincounselor]

Second try:

http://www.awc.org/codes-standards/calculators-software/spancalc

 

[tom-ky]

Second try:

http://www.awc.org/codes-standards/calculators-software/spancalc

From the looks of that it seems 2 x 8 would be needed.

 

[padroo]

I am not an engineer but anytime you are working with any span several things need to be considered and the one I didn't see is the wood species. Any recommendations on wood species out there.

 

[ard]

#2 Doug fir seems the most readily available, although it may vary with regions

 

[James-W]

This may be a bit of an overkill, but I think if it were me I would go with 2X12's and 12 inches on center. My thinking is that later on you may decide to put more weight up there than you had originally planned on. If by some chance you do end up with more weight up there, then having the extra strength will come in handy. If you don't end up putting more weight up there than you planned on, nothing is lost except for the extra cost of materials, which won't be a fortune.

 

[bczygan]

Still don't understand the layout.

 

[GMCGarage]

Probably only go 6-8 feet floor as I will lose usable height.
Planning on 16" centers.

Just general storage, maybe some parts but nothing really heavy planned but want to be safe.

2x12's @ 12" on center would be best

 

[tom-ky]

Still don't understand the layout.

In this pic the red line would be the joists and the blue line would be open except for posts. So basically a long shelf above the enclosed room.

 

[bruincounselor]

2x8 seems adequate for light loads. 2X12 seems like overkill to me. A different chart I'm referencing this morning allows 2X10's (Doug Fir/Pine) on 24" centers for residential flooring.
Proper blocking can help with deflection.

 

[GMCGarage]

2x8 seems adequate for light loads. 2X12 seems like overkill to me. A different chart I'm referencing this morning allows 2X10's (Doug Fir/Pine) on 24" centers for residential flooring.
Proper blocking can help with deflection.

2x6's would work for light load.

 

[bczygan]

In this pic the red line would be the joists and the blue line would be open except for posts. So basically a long shelf above the enclosed room.

Still need more info.

Is that a continuous wall on the left? Or is it open?

How long is it?

What is the width? In other words, the length of the red line.

Is the entire roof self supporting and free of this?

What ceiling material under the joists?

Photos would help.

BTW, none of the above answers are correct. They cannot be without more info.

Bill

 

[bczygan]

A note to others.

You cannot determine the joist size without specifying the loading, span, spacing, species and deflection limit.

Then, if there is an opening below, you need to design the beam or header and support for them.

And then the ledger and it's fastening needs design.

Bill

 

[mike93lx]

A note to others.

You cannot determine the joist size without specifying the loading, span, spacing, species and deflection limit.

Then, if there is an opening below, you need to design the beam or header and support for them.

And then the ledger and it's fastening needs design.

Bill

Sure, but if OP wanted certified plans or an engineer's sign off, this is the wrong place to go. The advice being provided is appropriate for the price paid.

Considering a 12' deck would require 2x8 at 16" centers, i would likely do that or 2x10 with blocking. If it can't be carried up to the loft by hand, it is probably too heavy.

 

[bczygan]

Sure, but if OP wanted certified plans or an engineer's sign off, this is the wrong place to go. The advice being provided is appropriate for the price paid.

Cosidering a 12' deck would require 2x8 at 16" centers, i would likely do that or 2x10 with blocking. If it can't be carried up to the lift by hand, it is probably too heavy.

You don't need certified plans or a sign off to build something, but to make sure it will do what you expect of it, you need something better than some guy saying "I built mine with 2x8's and it never fell down", or "2x12's ought to be strong enough". Capish?

So what is the load on your 12' deck? What is the deflection limit? What species and grade of wood?

You need to account for all the variables to get a measurable result.

A 2x4 will span 20'. But what will it support? How much will it deflect?

There is no reason you can't get a valid answer here. I give them often. Or your local lumber yard can do it.

The thing here, is to sort through the chaff to find the wheat.

Any answer given here, without all the correct questions answered first, is invalid. Any answer given without all the qualifiers is also invalid.

But it isn't rocket science. Anyone here can look up the charts and calculators and plug in the numbers and get the right answers.


Bill

 

[GMCGarage]

Sure, but if OP wanted certified plans or an engineer's sign off, this is the wrong place to go. The advice being provided is appropriate for the price paid.

Considering a 12' deck would require 2x8 at 16" centers, i would likely do that or 2x10 with blocking. If it can't be carried up to the loft by hand, it is probably too heavy.

Thats the worst advice given yet. I can carry about 50lbs up steps. but I can do it 400 times. Is 2x8 going to be good enough??

Bill is right, give proper info, you will get a proper answer.

 

[bczygan]

So let's design these joists. Can't do any beam or ledger without more info.

Let's assume a typical residential floor live load of 40#/SF and a dead load of 10#/SF.

I use 3/4" T&G plywood decking and limit the spacing of joists to 16"o.c.

Assume no finished drywal ceiling below and you can use a deflection limit of L/240.

Big box stores typically carry SPF #2 and better lumber, so use that for economy.

If the span is 12', as indicated by the red line, then using the calculator linked below, and the above variables, 2x8's will span 12'7". Deflection will be .6". Set joists with crown up, glue and screw and stagger decking and provide solid blocking at decking joints and midspans of joists.

Now you know exactly how much deflection there will be with the materials and loading you selected. That's the whole purpose of the exercise....to KNOW.

Bill

http://www.awc.org/codes-standards/calculators-software/spancalc

 

[bczygan]

Also note that this will hold 40 pounds per square foot of evenly distributed load plus the weight of the structure, which is allowed at 10 pounds per square foot.

If the space was 10'x12', the total evenly distributed live load could be 4,800 pounds, and still deflect only 6/10 of an inch. It would still not be near collapse.

If you were going to load it near limits, or want more load capacity, or want to cut the springy feel, you could go for a stronger species and/or grade, space closer, use the next deeper member, cut the span with a beam or use engineered lumber, or a combination of the above.

Bill

 

[-Brent-]

I ran almost exactly what Bill writes, above. But because I was about 5" longer span, I went with 12" OC. Even before blocking that sucker was solid. I'll never get close to the calculated load max and if you're putting run-of-the mill part storage up there, neither will you.

 

[-Brent-]

Nobody asked, is the interior load bearing wall built, yet?

 

[bruincounselor]

Anyone here can look up the charts and calculators and plug in the numbers and get the right answers.

Yup. Why I provided a link. It's a shed, not a rocket. OP can choose his own variables and tolerance for safety margin.

 

[tom-ky]

Nobody asked, is the interior load bearing wall built, yet?

No, you have any suggestions? Was planning on a 2x6 wall.