I-joist application question

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  #1  
Old 07-02-05, 11:18 AM
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I-joist application question

Hello all,

I'll get right to the point. I'm getting ready to build a home I designed. I basically designed the floorplan, took it to a company that does lumber packages for new home construction, and they came up with the I-joist (for flooring) and truss layout per my input. Actually, they sent my plan out to the company they use for their truss and I-joist layout. My question is, the I-joists they call for are 9 1/2". My longest span is 34'-7"(outside wall dimension). I looked up the I-joist they used, an AJS20 @ 16"o.c. which on my paper work says is rated @ 40-20 floorloads and a liveload deflection of L/480. Well the chart I saw says it WILL make the span I need(forgot to mention there is a steel beam centered between the span, so the span is actually just over 17')but the way I read it it has floorloads @ 40-10, and a liveload deflection @L/360. Cost is at $5500 for all joists, lvl's and hangers to frame the stairs in. Ok I guess that wasn't right to the point but here are my questions....

1. What is the difference between a 9 1/2" joist that will make the span I need and one that won't? I noticed that company's have different types of each joist and was wondering what makes one joist of the SAME depth able to make a greater span than another(How do they make it stronger??). However it's done I'm sure it adds cost, which leads me to my next question...

2. I noticed in my research of I-joist spans that any 11 7/8" depth I-joist will make the span I need(read..the WEAKEST 11 7/8" I joist will make the span I need compared to the STRONGEST 9 1/2" I joist made). Do you think it would be possible to save money by suggesting to the company to go with an 11 7/8" I-joist?

3. Am I simply missing something? In all my research(done on the internet)on I joists it just doesn't seem that the 9 1/2" I joist is the right choice for that span.

If you need more info please let me know. Also, if anyone is from the S.E. portion of Michigan and in the business of Design/architecture and wouldn't mind looking over my plan(for possible suggestions and a question/answer session) I would gladly drive to your location and pay for lunch per your choosing....

I guess that's it for now, I'm sure I'll come up with more questions later...thanks all...

Ron
 
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Old 07-02-05, 12:14 PM
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I-joist application question

There is more to I joists and trusses than just depth and thickness. Lumber grades and connectors are factors. The criteria used for other things such as deflection are importmant factors since it is not always a question of strength. They may be seing this in your plans that you are not aware of. You are just looking at tables while there are other factors such as concentrateload applications and load reduction factors.

I suggest you ask the supplier to give you the criteria used in the selection or to explain why there is a difference between their design and your internet design.

If you are not happy with their explanation get a proposal from another supplier and see how this agrees with your ideas.

Dick
 
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Old 07-02-05, 10:55 PM
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STUB,

You're a neighbor I see.

I am unfamiliar with the series that they are referring to. Besides the chart was done in 2003!

I've look at the chart you mentioned and I find that you may have overlooked something.

The AJS-5 in a 9 1/2" TJI will span the distance of just over 17 feet is IF the TJI's were spaced at 12" O.C. Based on your span, the 9 1/2" does not span that distance and be structurally sound. At 16" O.C. the 9 1/2" would only be good up to 16 feet. Even then, I would size up as you get too close to what they may span to but I like a solid floor - no bounce! I think they have done this as well - sized it up.

Based on the span and the size required, they have done it correct. They 11 7/8" which at a spacing of 16" O.C. which will span up to 18'-3". The AJS-10 would be my choice.

The AJS-20 seems to be the choice they estimated to do the job and do it well. Yes, cost wise it's more. The issue is what else is going on within the plans for them to consider these.

I always use these - http://www.trusjoist.com/PDFFiles/2025.pdf

Send me some plans to look at but in all honesty, when you give plans to a major yard, they do have some good folks who strive to ensure that what is required will be estimated in the take-off. This means even if your plans are wrong or undersized.

Does this help?
 
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Old 07-03-05, 05:19 PM
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i'm in se mi too. fingerle lumber in ann arbor has a guy on staff that does this type of value engineering and design.

different sections can have different strengths for the same depth by using a thicker web, or larger flange to the wood I joist. or even stronger wood for the flange.

you can do the math to compare the taller joists to the shorter ones - if you can use fewer of the taller ones, they might be cheaper (24" o.c. instead of 16" or 12" o.c.)

I think asking fingerle will get you there really quickly though. good luck
!!
 
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Old 07-03-05, 06:11 PM
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trance,

Personally, going 24" O.C. is asking for trouble, in my opinion. I would never go larger than 16" O.C. for a floor system regardless of the height and what load it may carry.

That joist spacing would be causing some flexing and depending on the finished floor, this would not be adviseable. Hardwood and Ceramic tile applications would be subjected to repair somewhere down the road.

Just some thoughts although I know you are suggesting trying to save money with the comments made. Sometimes, saving money is not worth the trouble.

Have a great 4th!!!!!
 
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Old 07-04-05, 03:37 PM
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Everyone, thanks for the input...

Doug, I will get a print to you as a pdf.format. I need to get my print scanned first so I can send it. I will try and do that tommorrow. Thanks for the offer. As for the I-joists, I'm sure they are right tho I will ask them about it. While I'm on the subject, does anyone know of other lumber company's that have 'packages' for homes? Would they also be willing to figure out my truss and joist plan? The company I'm going thru now did not charge me a dime for figuring out any of my layouts. I would like to get at least one other estimate on my print. I just went with the current company as my brother used them when we built his house a few years ago and he was pleased with them. They are also only about 6 miles away from the build site....Thanks again,

Ron
 
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Old 07-04-05, 04:12 PM
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STUB,

When say "packages for home", I am first recalling such a word "package" for homes that have been designed or marketed by a said yard. No changes could be given and the whole lumber package was specifically for that plan.

Your's on the other hand is not a "packaged" home, in my definition of the word. It is a "custom home" that must be assembled in a material take off.

Since you designed the home, as I do as well, the plans would be sent to a major yard, like John's Lumber, Wickes Lumber or National Lumber, where by they give drawings to the truss people to determine what is needed. The drawings should have a floor joist and roof framing layout of which those items would be reviewed by an Engineer of the truss manufacturer. They are the ones that provide the seal that the Building Inspectors want to look at. They do not charge for doing a estimated cost of the project but they won't provide a material take off unless you buy from them. They provide a bid like everyone else at no cost.

I see no difference in using the latter but if your brother had good luck, use them.

Send me those plans and I'll look at what you have.

Happy 4th of July!
 
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Old 07-04-05, 05:05 PM
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Doug,

I am familiar with the packaged homes you talk about. I see that how I worded it is sort of misleading. What I meant was the company I'm using basically gives you a discount by using them(the lumber company) to buy most of the materials for the home, hence my wording of a 'package deal'. Not only can they supply all lumber, but they can also supply all windows, insulation, doors, etc.

As for my drawings, all they consisted of when I turned them over to the lumber company was a floorplan with all door openings. They had NO truss or joist layout on them. The I-joists I could have done as my home is basically a rectangle with no inside load bearing walls, but I wasn't sure how to do the trusses. I had an idea, but thats all. I discussed how I wanted the home to look, the type of ceiling I wanted, etc, and the rep. I dealt with gave this information to their truss people who in turn came up with the drawings I now have. This is what I was wondering if other company's would do. If I just handed them my floorplan, told them I need an estimate on an I-joist and truss layout for my custom home, but by the way you have to figure out the I-joist/truss layout, would they do it? Anyway, I'm just sort of rambling now I guess. I will get my print to you asap...thanks again for all your input...

Ron
 
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Old 07-05-05, 07:52 AM
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Here is some I joist info for you

When you have a multi-span situation like your the floors are loaded for all load cases. Since the dead load is applied on all cases a beam may actually span further in a multi span aplication than it would if it is a simple clear span.

Several differences exist between I-joist companies. The flange and web are made of several different types of material so calculations may vary on this. Also Engineers are like doctors every one opinion varies slightly so one company may have a more conservative engineering approach than another.


I think you would be better off to go with th 11 7/8 joist. The deeper joist doesn't seem as maxed out and therefore will likely deflect less.
 
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Old 11-25-07, 10:25 PM
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how far can i-joist span when there used as 2 nd floor
 
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Old 12-03-07, 11:09 AM
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depends on depth and loading and spacing

the answer to your question depends on the depth of the beam, the spacing and what it is used for. Another serious consideration is how much deflection (sag) is acceptable to you. Code for floors is l/360 for live load but I think that allows too much deflection. I would use a max of l/480.
 
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Old 12-04-07, 07:44 AM
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I-joist spans, any joist type for that matter, do not change depending on what level of the house they are used on (1st floor, 2nd, etc). Go to TJI's website and download some spans tables, they are pretty easy to interpret.
 
 

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