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I-Joists Vs Floor Truss?

john7g's picture

If you had your choice which would you choose for floor framing?  Wood I-Joist or Floor Trusses? 


Seems like trusses require a little design & fab lead time.  I like the idea of the open chords of trusses but maybe I'm missing something. 

(post #77057, reply #1 of 82)

From my perspective -

Advantages of I-joists -

1. Readily available and relatively cheap

2. Long spans are readily available - We sell up to 48'

3. Cut to fit in the field

.

Disadvantages of I-joists -

1. fire performance

-------------------------------

Advantages of floor trusses -

1. Lots of room for mechanicals (Particularly in deeper depths)

2. Least labor to install

.

Disadvantages of floor trusses -

1. Lead time can be a problem

2. Not easily modified in the field

.

.

There are probably others, but that's all I can think of at the moment.

The First 40 Years Of Parenting Are Always The Hardest.

(post #77057, reply #3 of 82)

Yeah but, Boss, I'm sure your point of view is skewed, being a truss designer and such. <G> 


I see ads for the i-josits but they never show all the extra labor required for blocking & such... you don't have to have a better product, just better marketing. 

(post #77057, reply #4 of 82)

The amount of blocking depends on the job. Most jobs that I deal with have no blocking at all. But we also mostly deal with one story houses.

What I say goes.
(Unless DW says it doesn't)

(post #77057, reply #8 of 82)

This'll be 2 stories above a basement.  I suppose if the truss designer were given an idea of preferred loc for HVAC ducting they could try to accomodate?

(post #77057, reply #11 of 82)

Rectangular HVAC ducts in floor trusses have to be roughly halfway between the bearings.

Generally I tell people that the rule of thumb is that if you want all your HVAC stuff in the truss space, the trusses need to be at least 18" deep. Otherwise you're gonna have problems.

Plumbing lines can be a problem even with 18" deep trusses, depending on where they run in relation to the suply and return air ducts.

If you REALLY want the HVAC in the floor system, I'd strongly suggest having your HVAC guy meet with the truss guy BEFORE anything is built. I've done it many times - It avoids most problems.

Regarding what you asked about 28' spans - The "Spec House From Hell" has 28' clear span floor trusses. They're 24" deep and 2' O.C. The floor is as solid as any house I've been in that wasn't on a concrete slab.

The basement is great. I really like not having a lot of posts & beams to contend with. The depth can sometimes be a problem when you're designing a house. But - Everything's a tradeoff.

While you're thinking about floors - Have you thread the thread on floor vibration?

http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=21010.1

Nobody Knows The Trouble I've Been

(post #77057, reply #18 of 82)

I was already kind of considering the HVAC guy being the first one to to talk to on this project, but maybe I'll just send him to the truss folks and we'll work from there.  I've been figuring on an 18" truss.  The floor plan was based on 2x12s for floors but the need to put everything in the floor lead me to the trusses but 24" was going require too much of an increase in the direction of the stair runs (already added 2ft) so I'm hoping it can be done with 18s with spans less than 22' ...but now after reading the link to your prior thread I'll have to see if I can make the stairs work with 24s. 


back to ciphering and thanks to everyone.

(post #77057, reply #19 of 82)

Why don't you give Openjoist 2000 a look. http://www.openjoist2000.com/ I am just getting ready to start construction of a 3000 sf home for my family outside of Philadelphia. Basement will be 10' Superior Wall xi system and prefab Nascor walls from Canada. The Openjoist my choice because it gives you the benefits of open web and I joist since it has 1' trimable ends.

John

EPStructures Inc

(post #77057, reply #25 of 82)

Very nice but the shipping on those would probably eat my lunch since the closest distributor is MI and I'm in GA.  Do they have provisions for HVAV ducting other than the trainlge creted by the web bracing?

(post #77057, reply #20 of 82)

John, you know, if you only need 12" of framing there is another option.  You can install all the mechanicals below the joists and soffit around them.  If layed out properly it can be a design element.  Huge expanses of flat ceiling are pretty boring anyway.

 


 


"This is a process, not an event."--Sphere


And I'm a legitimate certifiable Tool [JOBSITE WORD].--Dieselpig

 

 

(post #77057, reply #26 of 82)

No argument there Woodguy, but I'd like to have the soffits as an architectural option as opposed to being forced into the issue.  I also think the HVAC might be more efficiently located in the floor (ie distribution possibilities). 

(post #77057, reply #21 of 82)

On a 22' span, I'd personally be happy with anything 16" deep or deeper. And I'm pretty conservative on floor design.

Never turn your back on a threatened danger and try to run away from it. If you do that, you will double the danger. But if you meet it promptly and without flinching, you will reduce the danger by half. Never run away from anything. Never!" [Winston Churchill]

(post #77057, reply #52 of 82)

"Yeah but, Boss, I'm sure your point of view is skewed, being a truss designer and such. "


I'm not in the business (mine is telecommunications), but I'd reach the same conclusions as Boss did. I'd love to have atruss-joist based home.

(post #77057, reply #54 of 82)

well.. quote it correctly
"Yeah but, Boss, I'm sure your point of view is skewed, being a truss designer and such. <G>"


<G> = a little sarcasm/humor in this case.


 

(post #77057, reply #12 of 82)

Thank you for the comparison.  I would be interested to know why I-joists have more of a fire problem - is it due to their thinner cross section?

(post #77057, reply #13 of 82)

Some of it is just my opinion. Some of it is experience. I don't consider myself an expert on it.

I did a thread once where I threw a piece of an I-joist on a brush fire:

http://forums.taunton.com/tp-breaktime/messages?msg=37987.1

I was really surprised at how fast it burned.

One time I met with an I-joist rep who worked for the dealer who sold I-joists to our truss plant. I was curious about the subject, so I asked him about fire performance of I-joists.

He said he didn't like to takl about it. If any of our customers brought it up, he suggested trying to change the subject.

.

So how important are the fire concerns? That's up to the individual. I don't think it's an important enough issue that I'd refuse to sell 'em. But I don't really like it, either.

He makes no friend who never made a foe. [Tennyson]

(post #77057, reply #16 of 82)

Boss,


I think there have been postings here re: fire vis-a-vis I joist. Some one said that Fire dept. personnel were instructed to evacuate the structure and fight it from outside if exposed I-joist were in use. Just hear-say on my part.

(post #77057, reply #17 of 82)

"....evacuate the structure and fight it from outside if exposed I-joist were in use."

When I've given presentations to firefighters, that's exactly what I suggest to'em. But I suggest it on EVERY building, regardless of the construction.

I don't see any point in risking the lives of firefighters just to sava structures.

I Love The Smell Of Sawdust In The Morning

(post #77057, reply #29 of 82)

Hey Boss, I've got 11-7/8" I joists at 16" spanning 17'-3" or 6"...can't recall exactly.

Anyway, one area of the house has "some" bounce, or vibration (I'm not sure of the difference).

Of course the truss guy (Okaw, out of Arthur, IL)said 19" is no problem for these I-joists.

The salesman from the yard was out measuring for doors, and said he would bring the truss guy back around, because he felt it was a little substandard also.

What is your casual recommendation?

Squash blocks mid span?

fill in the webs with ply?

Box the whole joist with ply?

Something else?

A medium to large guy named Alan, not an ambiguous female....NOT that there is anything wrong with that.


Edited 3/30/2007 9:55 pm by bigal4102

A medium to large guy named Alan, not an ambiguous female....

NOT that there is anything wrong with that.

(post #77057, reply #31 of 82)

I ike to limit 11 7/8" I-joists spans to 18'. You're under that limit, but not a whole lot. But I would typically expect your floor to be fine.

What's the situation with the house? Still being framed, partially done, or is someone already living in it? The reason I ask is that the vibration may change once things like flooring and furniture are in the house.

A beam can contribute to vibration. Is one end of the area supported on a beam? If it is, what are the details on the beam? (Size, type, post spacing, etc.)

I don't go for trying to beef up existing joists with plywood. It might possibly work in some cases. But it's basically guesswork, and I don't recommend something unless I'm sure it will work.

Stiffness comes from depth, not strength. Since adding stuff on the sides of the I-joists doesn't add depth, I wouldn't expect it to increase stiffness measureably.

All socialism involves slavery. [Herbert Spencer]

(post #77057, reply #33 of 82)

Comparing I-joists to factory floor trusses, my impression is that a stiffer floor can be had via floor trusses vs. I-joists of the same height.  Care to comment?


BTW - one disadvantage to floor trusses is that the floor system can't really be insulated effectively - OK - maybe with a spray in product. 


Also when talking about lead time - the big deal comes into play when it turns out that a truss (or several) were designed (and delivered) incorrectly, and say for example are 3" too short.  The order back can be a killer, although my truss supplier usually has 2 or 3 day turnaround on such a screw up.  Makes framers very unhappy and rightfully so.   As you know, for joists that are too long, a field fix can often be engineered but even that is usually a minimum of a 4 hr delay.


Also, just for the clarifications for those not real familiar with floor trusses, when you said deep floor trusses can cause design problems, (or whatever it was that you said) one thing it equates to is more step risers.  For other than large houses, extra feet of length of steps is a BIG deal.  


Another comment for the general population here:  Even with, say 18" floor trusses putting plumbing and HVAC in the same floor system can be problematic, since if the plumber needs to put in a long horizontal run of pipe this precludes ducts from being run in that area.


Don't get me wrong - I prefer using custom floor trusses if the situation is right.

Matt

(post #77057, reply #35 of 82)

"my impression is that a stiffer floor can be had via floor trusses vs. I-joists of the same height. Care to comment?"

Yup. I'd say that's absolutely, positively, not exactly right or wrong.

For instance - What brand I-joist are you talking about? Every manufacturer has 3 or 4 different Series of I-joists in different depths. Each one has different characteristics.

With floor trusses - Are they low grade SPF chords, or high grade SYP? How much loading are they designed for?

Have you read the Floor Vibration thread? Based on what I presented there, I believe stiffness is MUCH more a function of the span/depth ratio than what the floor members are.

CUBS = Completely Useless By September

(post #77057, reply #39 of 82)

Thanks Boss.  Good point about the different series of I-joists.  I think here, the ones with the 2x4 sized flanges are special order and I've never seen the ones with the 2x2 sized flanges, so I forgot about that.  We use LP and GP I joists around here.  BTW - yes I've read the floor vibration thread - maybe about 4 times.  The first time being when it was at the top of the current topic list...

Matt

(post #77057, reply #36 of 82)

I know you don't agree with me on this, but I gotta throw it out anyway.

I have had several experiences where adding strapping under the TJIs decreases the defl;ection and the vibrations.

And it is an easy solution most of the time.

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #77057, reply #49 of 82)

I don't necessarilly disagree with you. I just don't recommend that anyone do something that *I* don't have firsthand knowledge or experience with.

Strapping falls in that catagory.

Ten percent of men prefer women with large thighs.
Another 10% prefer small thighs.
The other 80% prefer something inbetween.

(post #77057, reply #40 of 82)

We are presently finishing the inside, no carpet yet.


My framers are as old school as it gets, they didn't like them new fangled I-joists anyway.


I have been told carpet will help, I have also been told I'm being to anal about it.I'll try to throw in a pic .



 


Piffin, do you think simple 2x4 strapping on the flat will help, or are you suggesting something else?


I am not against trying something simple as this "problem" is so negligeble, that several people don't recognize it as a problem at all.


They called me anal about a dry basement to, but it is still dry so far.....:>D


A medium to large guy named Alan, not an ambiguous female....NOT that there is anything wrong with that.


Edited 3/31/2007 10:42 am by bigal4102

A medium to large guy named Alan, not an ambiguous female....

NOT that there is anything wrong with that.

(post #77057, reply #43 of 82)

2x4s would work. We usually use a milled 1x3 sold here as strapping. You could use 1x4 too.

The thickness is not so important. What you are doing is turning the floor system from a platform into a thicker diaphragm. The whole floor benefits from having things in tension both ways when somebody walks orjumps around upstairs.

Strapping is the norm here in NE and offers many benefits. Added strength is one, sound isoation is another, better attachemnt points for the sheetrock is yet a third.

The straping goes on perpendicular to the joists at 16"OC normally. aids performance in much the same way as blocking, bridging, or strongbacks

Hey, that brings up an idea - did your old school framers install the strongbacks in these web trusses? That could be a part of your problem. I al;ways notice a difference in strength just in the way an open deck walks when we add the strongbacks.

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #77057, reply #46 of 82)

We can get 1x3's here, but they are pretty ratty, sold as furring, but not intended for what you easterners use them for, they aren't usually very straight and not close to clear.

I have I-joists, and my framers did check into necessary blocking, and we were told none was needed.

What are you calling strongbacks? We used strongbacks, or stay lath in the roof trusses, to keep them tied together in the middle, and bottom chords, but I don't understand for I-joist, or deck use.

The yard guy, said they sometimes specify squash blocks, but strapping would be alot simpler.

To jump in on you and Matt's fuel debate, here in the midwest, propane is king, natural is usually available in town.

Just like the strapping for drywall, regional differences are pretty significant.

A medium to large guy named Alan, not an ambiguous female....NOT that there is anything wrong with that.

A medium to large guy named Alan, not an ambiguous female....

NOT that there is anything wrong with that.

(post #77057, reply #47 of 82)

I got confused - thought that you had open web trusses which is where you would use a strongback.

Squas blocks wouldn't do a thing for you IMO.
Solid blocking might but would be hard to do.

So 2x4 would probably your best bet regionally speaking. Your strapping sounds similar to ours tho.

Matt and I were just copmparing notes, not arguing in the least. I know about regional diffeernces too, having lied in FL, TX, CO, NY, and more briefly at stops in between.

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #77057, reply #48 of 82)

Screw the subfloor down with 2-1/2" screws. 


I-joists for some reason seem to be stiffer if the subfloor is screwed down. 


 


I will remember before I forget. 

Matt- Woods favorite carpenter. 

(post #77057, reply #50 of 82)

That 33' long area - Is that ALL a bearing wall? Or is part of it a beam?

Vision. Tell people you have it - Employers love that crap.