Second Floor of Shop I-Joists or 2x12 Lumber

[Andrew Joiner]

I just got the quote from my lumber yard on my 19'x30' floor system. I'd heard that I-joists were better and not much more cost. I liked the idea of the lighter weight vs solid wood as I'm hoisting them up 12' in my existing 26' high ceiling shop. I'm studying all the information I can on installing I-joists as I've never worked with them.

The cost is $1984 for I-joists and 5"x12" LVL beams. The I-joists 16''OC span 19' clear and rest on LVL beams at each end. The 4- LVL's span 14' between the huge steel columns that hold up the 27' high roof. This is the specs from the I-joist supplier to meet 40 psf live load/15 psf dead load. This meets residential code for a floor full of people and furniture, all I'll ever need.

Then I priced 2x12 joists 20' long. I can make up my own beams from
4-2x12's glued and nailed. I'd put in posts so I'll only span 7' with the beams. This chart:
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
says I can span 19'11'' with 12''OC joists. All the charts for decks say I'm OK on joist span, but the made up beam spans all say 16' maximum joists can rest on the beams.This may include cantilever. If not I'll add more posts.

The price for 2x12's is $784! Way cheaper. I'm going to have a carpenter and the lumber yard manager(our best friend) look at the whole final plan.

I would rather use solid lumber. I know how to work with it. Framing the stair opening would be easier.

The main downside is I'm close to the maximum span and the floor may feel bouncy. As long as it meets code I don't care. I'll use it for minimal storage. I mainly want it for the ceiling. It's hard to heat and light a shop with 26' high ceilings. The other downside is I can't find 12" wide insulation batts so may have to cut 24", but to save $1200? No problem.

What would you do?

[Jim Becker]

My shop building uses I-joists and they are great. These are 22' joists, 16" tall and spaced 16" OC. While they may cost you a little more, the span they offer is just great. I-joists are also more forgiving when it comes to running wire and pipe through them in case that is a factor in your shop. They are also lighter to work with than big, long 2x12 boards, but yes, a little different. While was not around when the building was put up by a contractor for the previous owner, I don't have the impression that they are hard to work with.

If you do have to go with the lumber and 12" OC, you can buy 24" insulation and just split the material down the center as you surmise.

[Jason Beam]

When you say I-Joist, are thost them things with a board on top and a board on bottom with a web of OSB in between?

If so, I say run from them. The only reason I needed to hear to condemn them forever in my mind was: Firefighters. Should, god forbid, your place catch on fire, those webs are GONE shockingly fast. This leaves your entire span supported by a couple 2x3's. A solid 2x will actually smolder for a LONG time before it's structural integrity is compromised appreciably.

If yer taklin' somethin' different, then ignore me. I dunno about scissor joists and such.

[Brian Effinger]

The main downside is I'm close to the maximum span and the floor may feel bouncy. As long as it meets code I don't care. I'll use it for minimal storage. I mainly want it for the ceiling. It's hard to heat and light a shop with 26' high ceilings. The other downside is I can't find 12" wide insulation batts so may have to cut 24", but to save $1200? No problem.

What would you do?

If all you are using this space for is storage, then I'd just go with the 2x12's. The strenght of these is also determined by the species. Douglas Fir-Larch #2 is probably your best bet. They are a little pricyer than S-P-F, but they are much stronger and can span further.

[Andrew Joiner]

Yes, Jason.
http://images.google.com/images?sourceid=navclient&rlz=1T4GGLJ_enUS216US216&q=i%20joist&um=1&ie=UTF-8&sa=N&tab=wi

If they were cheaper I may use them and risk the fire weakness. I can see how you may be biased with your last name! Glad your not named skinnywimpysliversandglue?

[Andrew Joiner]

Douglas Fir #2 and better is the grade. Around here it's all Doug Fir and the long stuff is usually 90% #1's. So it's good on the species.

It may exceed the chart on spans,but the charts don't list all Doug Fir.

[Andrew Joiner]

Just checked the AWC span chart and #1 Doug Fir-Larch spans 21' so that helps.

[Greg Cuetara]

When you say I-Joist, are thost them things with a board on top and a board on bottom with a web of OSB in between?

If so, I say run from them. The only reason I needed to hear to condemn them forever in my mind was: Firefighters. Should, god forbid, your place catch on fire, those webs are GONE shockingly fast. This leaves your entire span supported by a couple 2x3's. A solid 2x will actually smolder for a LONG time before it's structural integrity is compromised appreciably.

If yer taklin' somethin' different, then ignore me. I dunno about scissor joists and such.

Jason,
Do you have research to back up your statements above? I would say that I joists and are mostly used in commercial construction but are also used in residential construction moreso now-a-days. Someone may correct but i believe that the webs are not just osb which has been cut down.

If there were that much of a problem with firefighters or fires I would think the firefighters would push to not be able to use them in construction at all.

As to the OP's question. If you are only going to use the space as storage space I would go with the 2x12's if the capacity meets the spans you have planned out. If you are going to be using the space as occupied space I would consider the I-Joists because you will get a stiffer floor. A lot still depends on the spans etc. If you push the limits of the joists, either I-joists or lumber, you will have a bouncy floor.

Another option would be to use the 2x material as joists but still use LVL's for your girders. I would have to see a plan to really get an understanding of what would be best. You have to decide if you want open space below or if you can stand more columns.

One advantage of the engineered lumber is that they do work exactly like traditional lumber. Some of the hangers are a bit bigger...I think Jim hit the nail on the head that you can drill holes in the webs, make sure you follow the manuf. recommendations, to allow for pipes, cables etc.

Greg

[Jason Beam]

I have a google search ... it's enough for me.

http://www.google.com/search?hl=en&q=I+joists+and+fire&btnG=Google+Search

I've heard firsthand from firefighters who've been injured due to a floor collapsing underneath them. It's fairly well known, as far as I can tell.

I don't need more than that.

[Joe Chritz]

The fire fighting business is hazardous at times. A lot more houses are built around here with engineered I joists then any type of solid wood. If the fire gets to the point where it is starting to destroy the web I would have to say it is well along and the structure is already in big trouble.

I am going to run it by a couple friends (who range from firefighter to chief) in a couple departments and see what they say.

As for using them, they are easy to handle and install. If it is live load (you will be working in there) make sure you over size them and the beams. For just storage it isn't as bad since bounce isn't a problem.

Span tables use different amounts depending on the amount of deflection allowable. I don't recall if it is i360 or l360 but that would be 1/360th of the span for deflection in the center. A 22 foot span with i360 is nearly 3/4" deflection. That would feel very springy under foot.

Joe

[Andrew Joiner]

Another option would be to use the 2x material as joists but still use LVL's for your girders. I would have to see a plan to really get an understanding of what would be best. You have to decide if you want open space below or if you can stand more columns.




Greg

Greg,
My shop is built like a pole barn, but with 7-steel posts on a foundation for "poles".
My site made beams made of 4-2x12's would span 14' between my existing steel posts that are in the side walls. The beams would be supported by blocking down to the foundation on each end and in the center.

The 19' long 2x12 joists are supported on each end by these beams. There are no posts in the middle of the 19' span, so the first floor is all open.


This is a tiny plan view. The x's are corner posts, the o's are center posts and the dashes are the 14' long beams. There's a large garage door opening on the right hand end.

x---o---x
o
x---o---x

[Mike Cutler]

Andrew

I would use the 2x12's with the cost differential being that great.
I have to wonder though, exactly which engineered beams are you looking at? Some are just that, a beam, others already have the cutouts in them for DWV, Electrical, water, and HVAC so that they are just installed. The manufacturer has done the work for you. If you do end up with the engineered beams, remember that there are a lot of "rules" about cutting them.
Maybe you were looking at more expensive beams that really didn't suit your purpose.

[Tom Godley]

First off the paralams / microlams / and I joists DO NOT work like traditional lumber. They must be properly sized then installed exactly as specified by the manufacturer/ engineer using the correct hangers, nails and stiffeners all in the correct locations. Protecting them from flames included.

Paralams / microlams - allow you to make headers and load bearing beams that would not be possible with standard lumber.

I have used these in quite a few projects over the years -- not always to my liking.


One example similar to yours:

I rebuilt a old garage that inside was 22 feet wide and I wanted it to be open space with no poles holding up the floor. The garage had block walls and conventional framed roof with a floor support wall between the bays. We removed all the old ceiling/floor and supports and framed a new 2.4 wall inside the block wall to provide support for the new floor structure (the old floor was sitting on the blocks) I was using a contractor that I used previously with excellent results and I purchased all the materials from an authorized dealer who provided me the material and drawings. I was a disaster!

Without going into all the details -- I had to rip out everything except the perimeter support walls and start over with a new contractor and my own engineer. I should have taken the roof off the garage and used engineered trusses -- it would have been cheaper and ultimately stronger!

What I have learned is that 22' is a long way to go unsupported for wood products of any type -- you get a degree of sag and bounce with any structure that off times is not acceptable to many people using the area above. Since you are using this for storage it may or may matter to you at all - but be prepared.

The floor above and the ceiling bellow MUST be glued to the I joist to stiffen the structure and all the rim support structure must be followed to the letter! The codes for deflection in a floor structure allow for so much deflection as to be IMO unusable for many uses.

I have used I beams in other area for floors/ ceiling with fantastic results because you can get them in incredible lengths allowing you to quickly install a floor structure with no breaks plus the products are light and stable.

Do continue your reading -- and think about paying a local engineer the very small cost of checking your numbers.

[Russ Boyd]

I would add to all the above...Whichever way you go, install a center blocking or even two rows of blocking between ALL joist. You wouldn't believe what a difference this will make in the bounciness of the floor. I personally feel the I joist will carry your span MUCH better than the 2x12 and will definately provide a more level floor. I have framed with both. I joists are simple to install. I'll also add that if you make your own beams, add a plywood piece in between the 2x12's. This will help to fir out to proper thickness and increase the stiffness a lot. Russ

[Joe Chritz]

http://www.raisedfloorliving.com/spantables-2.shtml

If you check the link above and the link below it appears at first glance that the 2x12 and the I joist are similar in span but the above table (#1 grade sawn lumber) is l360 where as the below (I joist) is l480.

http://www.trulinetruss.com/html/body_floor_span_tables_-_ijoist.htm

That is a difference of almost 3/16th's, .63 -vs- .475 flex in the middle.

It is all going to depend on what you are doing upstairs. Bouncing floors are no fun to live or work on but for a storage area it is fine.

I don't recall how much flex is OK before it starts to feel bouncy but it isn't much. You can also help with flexing if needed with extra briding, x braces and/or using plywood or OSB ceiling material underneath. Somewhere I have a book that gives a lot of info on joist flex but it is packed away somewhere that I can't remember. :rolleyes:

Joe

[Larry Edgerton]

I have installed thousands of feet of TJI's and for my own house I used hemlock. I just like wood better for many of the reasons listed.

Keep in mind that the install will be a mornings work, and then it is just a memory. Don't let one short, fleeting period of time affect your decision.

[Randy Cohen]

I used i-joists to frame the floor in my house. they are 32' long and 12" deep on 19.2" centers. they were very easy to install. the floor is very solid feeling. there is no blocking used along the span. the utilities were very easy to run. the parallam in the middle was pretty heavy though.

[Dave Sepucha]

From an engineering perspective, I think I Joists are great. They are very easy to work with not to mention light. They can have a bit of springiness (bounce) in floors but don't thing that would really be an issue for your install.

But I believe Jason is right, they can apparently burn VERY fast. I was doing some research on them and came across some of the articles from fire fighters. If you do have a fire, one could argue that the damage is done. But if you have I-Joists the structure apparently won't last long. I have no first hand experience with fire and I-Joists, just relaying the info I read.

So it's a trade off. FWIW, I have I-Joists throughout my house.

[Tom Godley]

So you have a span of less that 16" feet -- maybe 14.5 ?

This will act much different than going out 20' without any support -- This is what happens when you have a double garage with only one door.

[Andrew Joiner]

Jason,
Have you seen this classic photo? Says a lot for solid wood.


Here's more:http://www.softwood.org/AITC_eVersion/EN/p3.htm

http://www.softwood.org/AITC_eVersion/images/G3a.jpg
Steel beams have melted and collapsed over charred timber beam, which, despite heavy damage, remains in place.

[Andrew Joiner]

I have installed thousands of feet of TJI's and for my own house I used hemlock. I just like wood better for many of the reasons listed.

Keep in mind that the install will be a mornings work, and then it is just a memory. Don't let one short, fleeting period of time affect your decision.

Thanks Larry,
From reading your posts in the last couple months I'd say we have a lot in common.
Your insulation experiment sounds great. Sounds like you went against the norm based on your own experience and won. Good for you!

When I was a kid apprentice in a millwork shop I'd always wonder why the "industry" did things the way they did. Yup sales, marketing and politics kinda complicate common sense. When I had my cabinet shop I saw a lot of gimmicks and trends come and go.

So when you said" for my own house I used" my ears perked up. I designed my house and the shop we're talking about. I built all the "inside",subbed out the framing. Because of zoning and the very unique design I got into some new material choices. When ever I could I'd choose simple time proven materials. That is best warranty you can get. If it works don't fix it.

Now I do respect technology and testing. I did use I-joists in my roof since it was the best choice for that span.

[Jason Beam]

huh! Check that out :P

I hadn't seen that one before. I have seen a few shots of the osb web having been burnt out completely and entire surface sagging dangerously (feet, not inches). Those were shot by firefighters. I believe they even mention them when training new firefighters, but can't say for sure.

Tried and True for me :D


Jason,
Have you seen this classic photo? Says a lot for solid wood.


Here's more:http://www.softwood.org/AITC_eVersion/EN/p3.htm

http://www.softwood.org/AITC_eVersion/images/G3a.jpg
Steel beams have melted and collapsed over charred timber beam, which, despite heavy damage, remains in place.

[Andrew Joiner]

I would add to all the above...Whichever way you go, install a center blocking or even two rows of blocking between ALL joist. You wouldn't believe what a difference this will make in the bounciness of the floor. I personally feel the I joist will carry your span MUCH better than the 2x12 and will definately provide a more level floor. I have framed with both. I joists are simple to install. I'll also add that if you make your own beams, add a plywood piece in between the 2x12's. This will help to fir out to proper thickness and increase the stiffness a lot. Russ


Mike Guertin (who I like) writes a lot of articles on framing. He says:
Solid-wood joist blocking will sometimes help reduce bounce, but the joists and the blocks need to be dry and the blocks must fit very tight. I purposely cut blocks a whisker too long and sledgehammer them into place. Nail them in a straight line, not staggered. You can add one, two, or three rows of blocking to help stiffen the floor.

I also found this on a deck site.
Solid Blocking: Blocking keeps taller joists from twisting onto their sides when heavily loaded.
By 2003 International Building Code (IBC), blocking is required every 8 feet for 2x10 and taller joists.

Blocking will add to my labor time, and the I-joists don't need it,but I have lot's of time. I've used blocking in the past because it does make sense.

[Andrew Joiner]

My site built beams are 14' long. They are like oversize headers and will be within my existing pole barn like walls. The beams will really only span 7' . I can block them down to the floor every 3 or 4 ' if I need to.

It's a question of time and material. 1 big beam spanning 14'. A thiner beam spanning 7' and center blocks acting like a post. Or lots of blocks acting like studs and the beam would be more like a top plate.

Remember my existing walls have horizontal 2x6 girts, not vertical studs.

Yes my Fir 2x12 joists will span 19' and they will rest on the beam/headers.

[Allen Schmid]

Andrew (and Jason),
Thanks for thinking of the firefighters in this equation...we have all just accepted the fact that most (if not all) new construction is being done with the lightweight floor trusses. Heck, they are so common that you are even finding them placed as roof trusses in some instances. In many cities across the country the code now states that there is a marking placed on the outside of commercial/large residential buildings to indicate lightweight trusses have been used. The fail rate during testing is almost a moot point as failure is going to occur with fire impinging on/into the joist space, it is always a guessing game as to how long the product has been under assault. Some people I know have not used the LWtruss because of their concern. With standard response times and the amount of heat these fires are generating these days we all presume the worst and hope we can make progress at a fire with the least amount of danger for firefighting brothers and sisters.
Jason, nice job on finding the NFPA info and testing.
Andrew good luck on your project.
Allen

[Anthony Smaldone]

I'm a Lieutenant in the FDNY. Let me say, if we were able to, we would ban Wood I joists from ever being made. They fail within min. of being exposed to fire. They are very dangerous to the fire Depts. throughtout this country. Main reason being, We do not know which buildings have them and which do not. They have killed and will continue to kill us.

[Larry Edgerton]

[quote=Andrew Joiner;1023754]Quote:


Mike Guertin (who I like) writes a lot of articles on framing. He says:
Solid-wood joist blocking will sometimes help reduce bounce, but the joists and the blocks need to be dry and the blocks must fit very tight. I purposely cut blocks a whisker too long and sledgehammer them into place. Nail them in a straight line, not staggered. You can add one, two, or three rows of blocking to help stiffen the floor.

The traditional method is solid at each end from the bond to the first joist, and then X bridging across the span. It is nailed on the top, and the bottom is left to be nailed after the rest of the weight is put on the floor, and things have settled, dried and shrunk into place. It is nailed just before being covered. Solid blocking will not be as strong as bridging as it will not fit as well, especially after shrinking,no matter how big a hammer you use.

The idea of bridging is to stop deflection, where sag starts, and to spread the weight out over several joists at any point.

I don't think much of the metal X bracing that is on the market. Another positive for X bridging is that no holes need to be drilled for wiring, etc.

[Darius Ferlas]

I asked our Chief Building Official where I work (a municipality), and the Fire Chief.

This is a gist of what they said:

CBO- good strength and span. Sometimes issues with delamination of elements, depending on the manufacturing process. Delamination is a concern especially when the joists/rafters carry a ceramic tile floor. His preference is webbed wood joists.

FC: firemen won't even try to walk on floors in a burning house where floors are known to be made of I-Beams. Too risky for them. His preference (to be expected) poured reinforced concrete :D

[Jason Roehl]

One thing I haven't seen yet in this discussion is the difference in feel between the two floors. An I-joist floor can be made very stiff (low deflection), but will still bounce due to the lack of mass--it will vibrate for some time after all motion on it has ceased. Solid lumber has more mass, but is more flexible, so it takes a much larger 2x to achieve the same lower deflection as an I-joist. Due to the higher mass, however, vibrations are dampened.

If someone has a china cabinet in their dining room, I can probably tell how the floor is constructed just by walking through the center.

[Rick Lucrezi]

I did not read all the replies so if I parrot some one else I appologize. The fire thing kinda lost me. Any way, I am builder and I will advice against the sandwhiching of the 2x12s. 20 years ago or beter we had great lumber and it was possible to get quality select 2x12 and with good wood its ok to make beams. Nowadays the 2x12 you commonly see at the yards is suspect at best. Not to mention the weight of marying 2 2x12s. We use BCI i joist all the time. They are light, strong and easy to install. They do cost more and with the additional cost of the brackets its a hard not to consider the options, but when your done you will have a perfectly flat floor, and ceiling and for running wiring or plumbing you only need to knock out the pre stamped holes. Drilling through 2 2x12s with all the nails is a real pain in the rear.

[Greg Cuetara]

I'm a Lieutenant in the FDNY. Let me say, if we were able to, we would ban Wood I joists from ever being made. They fail within min. of being exposed to fire. They are very dangerous to the fire Depts. throughtout this country. Main reason being, We do not know which buildings have them and which do not. They have killed and will continue to kill us.

Anthony,
Are Wood I joists banned in NFPA? Is this something that NFPA is trying to do right now? It sounds like the problems are with the OSB. Is that correct? If OSB is that much of a problem are there any issues with using OSB for roofing and flooring rather than regular plywood? I would think roofs made with OSB might go up in flames faster and make it even more dangerous....yet another reason in my mind to use real plywood as a roofing material. Is it just the I joists which have the OSB web which are a problem? I know they also make I joists with tubing as the webs or 2x material for the webs. Should OSB be banned altogether?

[Rick Lucrezi]

One thing I haven't seen yet in this discussion is the difference in feel between the two floors. An I-joist floor can be made very stiff (low deflection), but will still bounce due to the lack of mass--it will vibrate for some time after all motion on it has ceased. Solid lumber has more mass, but is more flexible, so it takes a much larger 2x to achieve the same lower deflection as an I-joist. Due to the higher mass, however, vibrations are dampened.

If someone has a china cabinet in their dining room, I can probably tell how the floor is constructed just by walking through the center.

Good point. I recently added a second floor in a barn using BCI at 24oc, and 3/4 edge gold. I have a laser level and had it set up to check the ceiling heights, when I walked through the room, the laser went crazy. I hadnt realized before how much vibration was in a floor system.

[Kerry Medeiros]

Like Allen said, thanks for thinking of the firefighters. I am Deputy Chief of a small department and we have many homes that have been built in our area in the last 10 years and I can't think of one that used dimensional lumber. When I built my home this summer I used iJoists. You need to follow the manufacturers recommendations in terms of protecting the joists from direct flame contact. This is where most people fail as in almost every home people finish the main floor and leave the basement until a later date. I finished my basement immediately. I drywalled my basement ceiling with 5/8 firegaurd which gives the ijoists added protection. I've attached a couple of pictures that we use in training new firefighters. The story behind the pics is that there was fire in a home under construction. Fire started in a construction heater and was contained to a limited area in the basement. Very little fire extension past the basement level. However the engineered joists were exposed. FD was on scene within 6 minutes and made entry 8 minutes from initial call out. The destruction of joists compared to the damage in the remainder of the house is incredible.

Hope this helps.

[Chris Weishaar]

Thanks for all of the info. As a designer I have been spec'ing TJI's for a few years now. As others have pointed out, it is hard to get decent 2x material anymore. I do like the fact that they are easy to work with and they are a very consistent product. I had not realized the fire implications but I will take note now to ensure proper fire protection is spec'd. I think this is consistent with many new products. For instance I see more and more projects that use spray foam as the insulation since it has so many advantages over other systems but the fire risk is also greater. As such the foam must be properly protected.

Another thing to consider in using the I joists is that there are often 2 span tables in the literature. In larger houses I do not rely on the span tables and instead I use a structural engineer to size the joists. The engineer is always very specific with the client regarding how much "bounce" is acceptable to them even when we are framing with dimensional lumber. In smaller projects I will use the span table showing the L/480 deflection instead of the L/360 which will result in a stiffer floor. L/360 is the minimum allowed by code and who wants a house that just barely meets the minimum legal requirements. I am doing this in my parents house now and those floors are rock solid! And finally I never let the lumber yard/manufacturer run the calcs on a house. If you notice they usually put some "weasel" words in the documents regarding the fact that everything is sized for the average span. By definition some of your spans will be greater and some less than the average. You can end up with some really solid areas and one or two bouncy areas.

Anyways, I don't think the I joists are going away any time soon. Like many "new" products they have advantages and disadvantages and it is up to architects, designers, engineers, and builders to work to make sure that the products are used correctly. I am telling my parents tonight to make sure the basement ceiling gets a layer of sheetrock as it is the only area where the TJI's won't be protected.

chris

[Brian Effinger]

Wow Kerry! Those photos are amazing. As an architect I find them really interesting, and will log those in the old memory for later. I usually don't spec, TJI's around here, but from now on, I'll make sure to add the fire-rated gyp board with notation on my drawings.

And Chris, make sure your parents use the fire-rated sheetrock, just like the attached garage (if there is one).

[Craig Summers]

I used to be a Maryland volunteer firefighter in the 1990's

In all of our firefighting classes they drilled into us the problems of the composite floor systems (http://www.everyonegoeshome.com/newsletter/2008/march/whatsit.html), particularly the wooden I-Joists. They must be protected from flame impingement, drywall being the most common UL rated fire barrier. Also, when sealing gaps/holes for utilities that could cause flame spread, (from wall cavities etc) make sure to use fire-rated sealants. The normal "great stuff" is not fire rated. However, they do sell one that is.

Francis Brannigan is considered the guru of fire and building construction. His books are considered the firefighter's bible. (http://www.amazon.com/Branningans-Building-Construction-Fire-Service/dp/0763744948)

Even the Wooden I-Joist manufacturers association (WIJMA) caution about the Fire problem (http://i-joist.org/fire.asp). And have a handy video on thier website.

WIJMA has taken a proactive stance on the issue of fire safety. A 10-minute informational video for fire fighters has been developed to address many fire issues related to modern construction.

Significant additional information on life safety risk to firefighters and occupants is needed. WIJMA is currently working with organizations such as AF&PA and CWC to address common fire performance issues across the engineered wood products industry.

~~~~~~~~~~~~
The fire issue aside.

To compensate for the other shortcoming of the springingess and deflection, Wood I Joists offer a solution.
The one advantage that no one mentioned about the wood I joist is its easier to get stiffer material, just needs to be taller. I think I remember Bruce Hoadley's "Understanding Wood" discussed that 2 2x8 was similar to one 2x10 in strength. So a taller joist makes a better floor, and you might consider that if you are splitting a 26' floor to ceiling height.
The original manufacturer Structural Wood Corporation (http://www.structural-wood.com/SWC_engineered_wood_I-Joists.html)has a handy table of sizes they make (http://www.structural-wood.com/divb-inventory-lists/EngineeredWoodIJoist.html).

~~~~~~~~~~~

In the issue of cheap and frugal, you might check if your local metal shop has any un-used steel bar joists, leftover from a job. (ordered wrong size, cancelled job etc.) If so, you could have them modify them (with engineer's calculation/drawings). I would bet they would part with them for a reduced cost, otherwise they would only get scrap metal value. You can screw or powder actuated fastener a plywood deck to the joist. Not sure if that would be cheaper, just an option.

[David G Baker]

Kerry's post made a believer out of me. If ya gotta use it cap it with fireguard sheetrock ASAP.

[Herbert Mulqueen]

First a little about me. I owned a roof and floor truss plant for 25 years and sold a lot of I-beams. Also built pole buildings, steel buildings and high end homes. Now I am doing honey-does for my wife. Of all the things I did I loved to build heavy timber trusses with 1/2 thick steel connectors plates.

I agree with most of the previous responses.

Lets talk about span, it is difficult to get solid lumber over 20 feet. So a room clear span assuming 6 inch walls would only be 19 feet wide. This does not make a lot of architects happy with dreams of large flowing spaces. First there was floor trusses and them I-beams. These usually went into cost competitive townhouses and homes.

Of course you could use heavy laminated wooden beams and then ladder in-between with 12"s for example. This works but is costly and creates a thick area between the ceiling of the first floor and the floor of the second floor. In some cases it could be 2 to 3 feet thick. And the beam might project into the room below creating a non flat ceiling.

I-beams are cheaper than floor trusses. I-beams are generic extruded item.

The floor trusses are custom manufactured to a height and length.

I-beams require end blocks to prevent crush of the product. Installed on site.

Floor trusses are faster to install.

The higher the floor truss or I-beam the stronger it becomes. This is very important. It is cheaper in general to have a higher truss than more lower height trusses spaced closer together.

The added height of the I-beam is not very expensive.

I-beams come with 2x2 and 2x3 and 2x4 tops and bottoms. The reason to have different size chords is just cost. What a giant builder wants is JUST to make code. Nothing extra. Cost drives the construction market.

I have a garage that is 30 foot clear span and has 23 inch thick ( high) floor trusses. 12 inch on center with two layers of 3/4 subfloor and 3/4 inch of 5 inch brazilian cherry.

There is no bounce and the room is very solid.

You can have your local building supply( forget the big box stores) and get a

recommendation on sizing. However give them some design information.

Size of bearing----such as a 2x6 is 5 1/2 inch on both ends.

span----------------inside distance from bearing to bearing

load----------------what is on top-----equals top chord load
what is on the bottom-----usually sheetrock
what is the live load-------people, machines, furniture , file cabinets filled with "stuff". The biggest problems I had was from accountants, lawyers, national geographic collectors who had lots of concentrated loads, water beds , full size snooker tables 6x12 with 2 inches of slate.

So tell the man what you are doing.

Usual bedroom load is about 55 total PSF

commercial loads run from 100 to 250 and up.

The room over my garage was designed for 300 pounds PSF with almost no deflection and no apparent bounce.

Nice thing about I-beams is that they are easy to install. Floor trusses usually are designed NOT to be cut. So the builders must build square straight walls.

I-beams are easy to use in tapering conditions. That is where walls are not parallel.

In the past we built roof trusses to 80 foot and floor trusses to 40 foot. These are all clearspan. We built some trusses for the navy that closed two tunnels and we had state police escorts for 150 miles closing the bridges.

It only cost money and you can get anything you want.

If I was looking for a large room with clear span area. For example 40x60

Get some used big steel I-beams 40 footers (tall in height) say 3 of them and then ladder them with tall I-beams or floor trusses. If you find 4 steel I beams you could ladder with solid lumber. Years ago I got a steel Ibeam from a old railroad bridge. 44 feet long 24 inches thick and about a little over 300 pounds a foot. It cost me under 500 dollars delivered. That thing weighed over 13,000 pounds and then a crane and welder to cut the beam. But I have a room roughly 44 x 58 in the basement.

You local building supply can help you and then take it to a structural engineer for review and suggestions.

Also remember to build big footers. I like like the german concept of 36 inches wide x18 inches thick and 4 pieces of 5/8 rebar. I have always used 5000 psi concrete for the last 30 years. Overbuilt yes for sure, but you can sleep at night. ( actually it is 1 meter by half meter).

Sorry for the rambling.

Herb

Ps. I built a gym for a church. The design was simple they wanted 120 wide and 200 feet long. Low height to be 24 feet and 40 foot clear in the center. No columns anywhere. get what you want try not to settle.
-

[Chip Lindley]

Wow, GREAT information here. You guys are reading my Mind! Now retired, I want to build a 32x32 dream shop/garage in what space I have out back. I have more Time than Money and wish to do as much as possible to save on cost and pay as I go,

The building will cost more to *look nice* (same siding/roofing/2nd story) because it is adjacent to my home. Otherwise I would just throw up a big metal building if I had land! I am not so blessed. Since extra $ must be spent on appearance I want to save wherever else I can, without compromising structural integrity. These are my ideas so far:

* 4" concrete slab floor

* 2x6x10' walls, 16 or 24"" centers?

* gambrel roof w/ 2nd floor for storage of heavy stuff i.e. hardwood lumber, machinery, (for now) but roughed in for toilet and electric for future efficiency apartment.

* upper floor supported by longitudinal homemade lam-beam, in 3 sections, 4-1/2x16x10'4" (made of 6 lams 3/4 OSB using plastic resin glue, lam butt joints staggered by 24"

* 3 Lam beam sections bolted together 1/4"x16x24" steel gusset plates, supported on 2 posts (4" heavy wall pipe with welded steel 3/8" top plates.

* Homemade I-beam floor joists (12"x16ft on 12" centers) 2 lams 3/8" OSB, butt joints staggered 24", 1-1/2"x1-1/2" top/bottom chords, plastic resin glue. (can I-beam halves be joined over center beam support?)

How am I doing so far?? After reading here, I do not think I am too far off. I appreciate any professional advice anyone can afford. Main concerns are with building my own structurally sound Lam center beam and I-beams as indicated? I am not naive, but believe much can be done to save money if the right materials and techniques are used when my time is FREE!

P.S. Certainly not my intention to hi-jack this thread! I guess I got carried away! I think I am right on track as the OP with same issues., with the DIY aspect.

[Craig Summers]

The other way to build strength into a wood joist is to sandwich in a steel plate (or two), called a flitch plate.

This is often done for garage door headers because of the long span and loads

http://www.mii.com/miilib/16/5/{5F2987B3-2E6E-40DF-93F8-5DEE6972E43F}.gif

Commercial sources for a pre-assembly:
http://www.betterheader.com/
http://www.readyheader.net/

Engineering info: http://www.structuremag.org/Archives/2007-6/D-From%20Exp%20Flitch%20Plates%20DeStefano-pac-5-10-07.pdf

If you want to make it yourself, go to the local steel shop and order a flitch plate. They can punch or drill the large holes quick and cheap. You need open span length +2 bearing sides. Normal maximum length is 20', longer will require splicing plates. Buy it undersized in height, example 9" wide plate for 2x10, 11" for 2x12. Thickness depends on strength needed, however going over 1/2" thick means it won't be flush in a 2x4 wall.

Typically a local steel shop will charge by the pound, expect about $ .75 to 1.25 per lb depending on raw steel prices (it is coming down now).

[Dave Zeigler]

I have a garage that is 30 foot clear span and has 23 inch thick ( high) floor trusses. 12 inch on center with two layers of 3/4 subfloor and 3/4 inch of 5 inch brazilian cherry.

There is no bounce and the room is very solid.
<snip>

The room over my garage was designed for 300 pounds PSF with almost no deflection and no apparent bounce.



No bounce? I should hope not! That's a floor system on steroids!

My shop has considerably less beef and has a 28' span (outside to outside). I used TJI joists 16" O.C. with a single layer 3/4" t&g plywood floor, glued and screwed. If memory serves, my joists are 18" high with 2x4 chords.

My shop is over a 3 1/2 car garage. I didn't want any columns in the garage, so I ended up using TJI joists due to cost and ease of installation. Most of the joists were installed by just me, my FIL (who was in his 70's at the time) and my "skycrane". The crane is mounted to my truck in the pic's, but it was reworked onto a big dolly to hang the roof trusses later.

I have a single row of blocking run down the center. I built the blocking using 2x4's, slightly oversized and trimmed each one to fit snug.

My floor is quite sturdy and I'm very happy with the results. I did not consider fire implications of the TJI joists, and I appreciate knowing that I should drywall the ceiling when money permits.

The building inspector was impressed with the solid feel of the floor when he did the final inspection.

I attached a picture of my blocking, taken while I was building them. I shamelessly copied the design from one found on the internet.

Close inspection of the garage door headers will reveal they are Flitch plate construction. I went with 12" tall, 1/2" thick mild steel. The supplier punched the holes for the bolts. I notched the studs to accomodate the fact that the steel was 1/2" proud of the 2x12's.

I really enjoyed building my garage/shop and like to refer to it as the "Garaj Mahal". LOL!

Fun stuff! Good luck with your project.

Dave