# Joist calculators?



## Steve in PA (Nov 25, 2011)

I'm looking at adding a 2nd story or loft to my 22x44 garage. I would need to peel off the current traditional roof, add 3 courses of block, lay new joists, and put on a gembrel roof.

I haven't been able to find a joist calculator online to see if I can span 22' with ijoists without putting in posts. I don't want posts because we park the cars inside but I want to use the 2nd floor for storage or workshop space.

Does anyone have any experience with ijoist installation or know where I can find a calculator?


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## farmerj (Aug 20, 2011)

I have a machinery handbook that gives the information. It's also available at your library.

I have also found that information when looking for deck loading for clear spans and joist spacing.

I won't GIVE that information as it's an engineering document at that time and the liability is more than I care to be involved with. But places I have looked...

I would recommend discussing this with an architect to be honest. It's got some serious engineering liability to it that needs to be handled by a licensed professional. That's why they get paid the big bucks.


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## Steve in PA (Nov 25, 2011)

I'm not doing it myself. I'm trying to get a rough materials list together before I solicit bids so I have an idea what to expect.


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## farmerj (Aug 20, 2011)

http://lmgtfy.com/?q=deck+free+span+length


That should give you some information. For 20'+ you are going to be looking at some engineered beams of one form or another.

http://www.menards.com/main/building-materials/engineered-products/i-joists/c-5662.htm


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## Steve in PA (Nov 25, 2011)

First one wasn't helpful...smarty pants.

I did find something from Georgia Pacific. IJoists are engineered lumber, so that was a given. I finally found something in the Georgia Pacific specs and their WI80 14" IJoist will meet L480 and L600.

I may still look at running a steel beam perpendicular for load bearing purposes. The $1000 would be worth the insurance. I could also use 12-12' ijoists.


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## farmerj (Aug 20, 2011)

there are plenty of calculators there. I don't know of a better way to share the links for google.

If you can find a better way without a link that's 5+ lines long, I'd like to know it.

Most of those pdf files are from county/city engineering offices and the state code requirements for freespan distances, joist spacings and the requirements for them.

It's how I went about figuring out how to built an attached deck to the house. Same thing for free span rooms if you aren't putting any interior walls in it.

If you are going to have interior walls, then you will have to put in supports under them to carry the load from above.


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## Steve in PA (Nov 25, 2011)

If thought you were being wise. Go here: tinyurl.com for making short url's

The calculators I was looking for were an automated version of the charts. Even though I was a Mechanical Engineering major for a short time I'm not a slide rule kinda guy. I respect the heck out of the old engineers but I didn't want to reinvent the wheel.


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## fishhead (Jul 19, 2006)

I would think there would be an online calculator just like for wiring.


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## farmerj (Aug 20, 2011)

Steve in PA said:


> If thought you were being wise. Go here: tinyurl.com for making short url's
> 
> The calculators I was looking for were an automated version of the charts. Even though I was a Mechanical Engineering major for a short time I'm not a slide rule kinda guy. I respect the heck out of the old engineers but I didn't want to reinvent the wheel.



Machinery Handbook if you can find a couple of older additions at a rummage sale are a windfall for doing things like this. All those guidances are in there.

The big thing is going to be the floor loading. What kind of a shop are you looking to put up there. THAT has to truly be answered first.

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

http://www.sawmillcreek.org/showthread.php?75333-How-to-calculate-load-capacity-on-construction

found those with this.
http://lmgtfy.com/?q=floor+load+bearing+capacity


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## Raymond James (Apr 15, 2013)

If I were doing a shop I would want to put in an I beam not so much for the weight above but to put a hoist on it. 

What kind of floor is the question to answer first.


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## joseph97297 (Nov 20, 2007)

I would entertain the ideas of a central post here and there. Great place to put outlets and such.

At 22 feet, that will be a nice span........


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## NorthwoodsMike (Jun 10, 2013)

We spanned 24' in out home using floor trusses, and only ended up costing slightly more than labor and materials for a beam system.

Have you looked into attic trusses?


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## Steve in PA (Nov 25, 2011)

NorthwoodsMike said:


> We spanned 24' in out home using floor trusses, and only ended up costing slightly more than labor and materials for a beam system.
> 
> Have you looked into attic trusses?


Attic trusses? Not sure what you mean.

These are the ijoists. http://inspectapedia.com/structure/I-Joist_MN-033-DJFs.jpg

I would love to find more info for open web steel joists as far as price but that's even more difficult to find. The 12K1 version looks to fit my needs, but I can't find anything about spacing either to do an apples to apples comparison.

Ex cost of 14" ijoist spaced at 16" vs 12K1 steel spaced at x inches.

The workshop area will be on the 2nd floor. Nothing major, just storage and standard woodworking gear. Guy Space.


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## NorthwoodsMike (Jun 10, 2013)

These are what my floor trusses look like. They free span 24' and are 19.2 OC.

















This is what an attic truss looks like. It combines the roof truss and floor joists.


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## Steve in PA (Nov 25, 2011)

Thanks Mike. Did you do those drawings? If you did, what program is that?

Do you have any problem with springiness in those floor trusses?

Wow, that's a lot of questions lol.

edit: One more question. What size (depth) are your trusses?


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## NorthwoodsMike (Jun 10, 2013)

No-I just pulled them from google. 

No spring whatsoever. The floor is extremely solid.

I think they are 16"


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## beowoulf90 (Jan 13, 2004)

farmerj said:


> *Machinery Handbook if you can find a couple of older additions at a rummage sale are a windfall for doing things like this. All those guidances are in there.*
> 
> The big thing is going to be the floor loading. What kind of a shop are you looking to put up there. THAT has to truly be answered first.
> 
> ...


One of the best references I have. I have a 26th edition at work and an older one at home plus other reference books..


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## haypoint (Oct 4, 2006)

As has been shown here, attic truss will help support the floor joists. My son is a mechanical engineer at a place that builds trusses. Ant good truss company can engineer and design a gambrel attic truss that will support the snow/ wind load for your area and the living space you hope to gain. 
It can be done. While it may be fun to research and draw sketches, in the end, the truss company will do it. 
It would be a costly waste of materials to put up an engineered floor joist and then add second floor walls, add a roof peak and gambrel sloped rafters. An engineered truss would be stronger with less materials.
A piggy top truss is needed when over all height of a truss exceeds legal highway load widths. In Michigan that is 16 feet. Note piggy top in picture of attic truss.


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## moeh1 (Jan 6, 2012)

You can get the I joist calculators right from the I joist manaufacturers site. I ran 28' clear span, solid as a rock, but that was their beefier "commercial" series with bigger sheeting and larger top and bottom pieces (2"x4"). Took a couple weeks to get them shipped in.


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## moeh1 (Jan 6, 2012)

I forgot to add, they wanted me to double up the smaller ones, same total stength and about the same price. Except that the skinny ones snap if you turn them sideways while installing and the two skinny tops are hard to nail thru without splitting.


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## wharton (Oct 9, 2011)

Steve, A few code considerations for building in PA. If this is an attached garage, you are going to need 5/8" OR fire rated 1/2" sheetrock on the ceiling and the wall that's common with the house. If not attached, you might have to sheetrock the ceiling, depending on what you use for floor joists, and beam, how many square feet of space you are dealing with, what you are calling the newly created space above, and what your local inspector is picky about. 

Two things to keep in mind. In living spaces, all engineered floor systems (trusses, I-joists, etc...) need to be fire rated, typically with a layer of 1/2" drywall on the ceiling, and 3/4" plywood decking on top. This does not apply to sawn lumber like 2x12s. A steel beam is also a fire issue and would need to be sheet-rocked for rating. This BTW, is a great idea in a garage, as steel fails quickly when exposed to the heat of a good vehicle fire. The final issue is intended use of the space. It is best to refer to any of this, when dealing with the code bureaucrats, as "Attic Storage Space". No mention of workshop, man cave, or heaven forbid, bedroom. I would speak to the inspectors before you start. A reasonable inspector, the right choice of material, and the right answers to "what are you creating this space for?" can literally make the difference between a reasonable project and a money pit. BTW, I build a few counties east of you, so as crazy as some of this sounds, it's all real, and tough to avoid. For example, a 22 x44 garage would need little attention from my local jurisdiction, since it's an unattached structure, less than 1000 sq. ft. In other locations the cut off is 200 ft. Now if I put a second story on an existing garage that size, it suddenly becomes a BIG deal, including having to dig up the foundation wall, and footer, for inspection, full drawings, permitting, inspections, etc..... Good luck, and stay cool.


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## Steve in PA (Nov 25, 2011)

Thanks Wharton. I was aware of the fire information from all the research I've done. Our township is very small and I'm friendly with the codes person. He told me things off the record before that make me think I won't have much if any problems with the township.

My "official" story will be that it's a roof replacement with an added storage area. You're the 2nd person to steer me to that. I'm proceeding with caution.


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## HMAN (Sep 15, 2008)

roseberg 400 series.... 14" i joists simple span will do 22'-3"thats inside of bearing.
16" will do 24'-8"

depending on what you stick up there i would go with 16"


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