Wood "I" beam spans ?

schiada · September 19, 2018, 06:29:18 PM

So I am working on the floor joists over a cement block basement.

Will wood "I" joist be ok for a 28'+- span ? Looking at the net. most would need to be 2 1/2" x 14" on 12" centers.
It maybe more a question about keeping the floor from having a bonce to it.

And can I do the same thing on the second floor ? Trying to stay clear span for the most part.The floors will have some walls but would like to keeep the basement clear.

Ideas ?

Thanks, Randy

MountainDon · September 19, 2018, 06:48:03 PM

Where I am the builders use more open web joists than the TJI type. One advantage of the open web design is there is no need to cut or drill holes for piping, wiring, or ductwork. I'm not sure if there are disadvantages. Looks like the ones I linked to as an example are available in up to a 30-foot span and the ends are trimmable. All the multiple story homes here use floor trusses, the main floor on slab.

The link is just an example. We have a local truss fabricator.

September 19, 2018, 07:58:41 PM

My local truss company was very helpful - just went in and told them what I wanted to do; took them a few minutes to tell me my design options and provide price estimates.

1akbig1bear · September 22, 2018, 11:33:07 AM

Schiada,

I am in the process of building a cabin with the same exact 28' span and used the TJI joists. I agree with CabinNick a 100% in the aspect that whomever you purchase your materials from will in fact help out with the question but also keep in mind they will always over engineer to protect themselves. The good news is that you will have a solid base to start with if you follow their lead.
Now, speaking from experience on my own build I would not have a 28' span without a center support. I would be curious to see your plans and the roofing plus interior design.
Here is a link to some photos I posted of my build and would be happy to share the blueprints I'm utilizing for my 28'x36' cabin. Simply copy and paste the link

https://imgur.com/a/mCLl0

Don_P · September 22, 2018, 02:49:25 PM

My experience has been that the suppliers of engineered products will offer you a code minimum solution first, so called "value engineering". This is how the free market works, he is in price competition with other means and methods at this point.

They may ask or you may look over their proposal and see higher deflections or lower design loads than you would like. With something like this they will come back in moments with the next solution. We've moved beyond the minimum, it will cost more but will perform to the higher specification, it is you who will make the call to "over engineer". When you are at this point in the conversation the tech is on board, this isn't a price shopper, we are designing a good floor, roof, beam, whatever. He then begins tuning the design in that direction. He knows more ways of getting where I want to go, the process might become iterative for a bit.

For instance, if you get a floor of this clear span specified, the first option is likely to be a deflection of L/360, to code. That is about an inch of sag. I would ask for about half that, a stiffer floor. If you've ever walked on one of those long span stiff floors it is like walking on a snare drum, that's no more fun than the saggy floor. To calm that down make sure the underside is sheathed and you need more mass, "mass damping", a double subfloor is one way. Run the numbers with a double dead load and there is one way to a better performing floor.

As much as possible, that isn't a floor I would build without cautioning that they might not be happy in the end. Ah and another popped into mind from that class, because floor vibration is a function of not just the joists but if they are supported by spanning girders and headers, that increases vibration. Design them to a deflection of L/600 or less.

The way the engineering of these products is done from a liability standpoint they will engineer the beams or joist or trusses but they are no designing what it is supported by other than to give minimum bearing areas. For instance on 1akbig1bear's they engineered the beams and joists not the posts and foundation. That can give a builder a false sense of security, they aren't scrutinizing that part of your plan, they are designing their elements not yours. Keep this in mind as you design, generally you are the engineer of record, you are subcontracting that element of design.

September 22, 2018, 03:39:24 PM

Well, I can only speak from my personal experience which was over engineered based on the material recommendations they came back with, utilizing my blueprints. I can guarantee I too was price shopping but based it entirely on ease of build. They absolutely did not provide a code minimum or value engineer solution and my building material supplier clearly stated this when providing the recommendation from the manufacturer. He specifically said "They will always provide a solution to protect themselves from suggesting something that may be just meeting code".

schiada · September 23, 2018, 12:43:06 AM

1akbig1bear,that is looking very good.Thanks for the link.

Have another post going and thinking of going with a center LVL or glulam from eve to eve with one support in the garage, and running 1/2 of the 40' to the gable wall of the basement to get the floor load out of the garage door opening.

Don_P · September 23, 2018, 08:51:49 AM

In the spirit of explaining how the legal stuff works. The supplier and staff have satisfied any liability concerns when he satisfies code minimums. Beyond that we are asking for higher performance than is required. It sounds like the supplier did that for you which is great, he designed beyond a minimally performing floor, it was not done out of a fear of liability. Much the same, I don't build strictly to code, I don't want to hear about my poor performing bouncy floor from the loafers at the country store.

1akbig1bear · September 24, 2018, 09:41:32 PM

Don,
I'm just curious, are you an attorney? I was wondering since your an expert as to how legal "stuff" works.

September 25, 2018, 07:10:51 AM

Oh no, I eat their lunch

. Well, looks like we're speaking plainly now. I'm a builder. I have been trained and tested and called as expert testimony on the legal stuff. I politely tried to clear up some confusion. How you choose to take that probably does inform us.

QuoteI agree with CabinNick a 100% in the aspect that whomever you purchase your materials from will in fact help out with the question but also keep in mind they will always over engineer to protect themselves. The good news is that you will have a solid base to start with if you follow their lead.

The thought that the supplier will exceed the minimum as a matter of course and provide a superior floor out of a fear of liability is incorrect. There is no fear of liability there, something else was driving that spec.

Think.

There is nothing wrong with some motivations, they can work in our favor. I try to find win-win solutions whenever possible, but it is never a bad thing to understand what is going on around you. It sounds like he took care of you well, that is good.

For the legal, the design is "according to accepted engineering practices" at code. Liability done with. You'll find that spelled out in chapter 3 of the IRC. Understanding the code specification and then being able to read and interpret the suppliers paperwork is never a bad idea, the numbers on the page mean more than the salesman. You've said the floor is better than code.. in what way?

To continue with that thought. If you put an engineered, to code or better floor on top of a non code foundation, is there any liability on the part of the supplier of that floor? Negligence is going to take care of that concern pretty quick. Another place this often happens is an engineered truss being placed on a non engineered house, there are specific design duties of the truss engineer and the building designer, understanding the handoff points is very often misunderstood.

Where all of this was going, pay attention to the details, if you are doing the designing strive to understand what you are doing.

NathanS · September 25, 2018, 07:41:19 AM

Just throwing in my experience, I went 24" OC for my upstairs floor. It had the unintended consequence of requiring a second layer of subfloor in the bathroom so I could put down tile.

If I had known that between the joist deflection was a thing for tile, I'd have thrown a couple extra 2x12s in the bathroom floor.

It is hard to keep track of all this stuff when building a house. Don giving experienced advice is a great help on this forum, sometimes we don't even know what questions we should be asking, though.

Bobmarlon · September 27, 2018, 09:08:59 AM

If you have your floor designed by a lumber yard they will give you a number rating telling you how well your floor will preform. I'm almost certain you should put in a beam that spans mid way. You will probably also need lvls for shear strength. For reference I am building a house with a clear 26 x 26' room on a first floor with another story above it. Highly recommend hiring an engineer being able to email somone who can give you difintive answers is great.

Also at the bottom of your plans from a lumber yard there will probably be a huge disclaimer that says you should get it checked by an engineer.