Author Topic: Joist choice: I-beam vs boards and girders vs truss joist  (Read 1833 times)

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Offline MTScott

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Joist choice: I-beam vs boards and girders vs truss joist
« on: April 08, 2016, 12:47:12 PM »
I'm making basic design choices now so I can estimate costs better.

I see many of you using a girder beam and smaller joists in some of your builds, even when there are methods of spanning the full width without (or so I think).   I'm curious what would swoon you one direction or the other.

I'm considering both 16' wide, and 20' wide plans at this point.  I've seen some builders place a girder beam and overlap the joists even on the 16' builds.  It seems you could easily span 16' without a beam.  At 20' wide there are I-beams that will span that well.  Is it so you can use smaller joist boards?  I can imagine cost is a concern, but by the time i add up the cost of beams, piers, etc... it is a wash.  Is it strength?  Does a 20' span on I-beams get spongy?

I'm curious what you guys have to say, on a 20' wide floor (x 30, 40, whatever), why would you go one direction or the other?  It seems to me that if the span tables say it'll do it, simply spanning 20' with I-beams is much simpler... but I'm new here :).

Truss joists are an option as well I suppose, but those boys are spendy.

Offline DaveOrr

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Re: Joist choice: I-beam vs boards and girders vs truss joist
« Reply #1 on: April 08, 2016, 02:46:49 PM »
When I was costing out my cabin I looked at Ijoists but the cost was triple what dimensional lumber was up here in Yellowknife.   :-\
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Offline Don_P

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Re: Joist choice: I-beam vs boards and girders vs truss joist
« Reply #2 on: April 08, 2016, 03:16:44 PM »
Dimensional lumber is better in fire. engineered joists are flat, straight, and can go long. Long spans do have vibration issues, I prefer shorter spans but people like larger and larger clear spans.  Although when you have a girder and a joist there are two spanning/ vibrating elements. Sheathing both sides of the joists helps a whole lot. We framed for one client with 24' open web joists that were annoying. He went over it with a second layer of subfloor and then a hardwood floor, that did dampen it.

Offline flyingvan

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Re: Joist choice: I-beam vs boards and girders vs truss joist
« Reply #3 on: April 08, 2016, 05:11:28 PM »
   My first build was all dimensional lumber.  The second, the floors were all TJI's.  As Don said, they were all perfectly straight.  They were stiff in compression, easy to move into place.    If you always cut the same end, all the knockout holes for utilities line up perfectly. 
    That said--
   When I break ground on building #3 I will go back to dimensional lumber.  I like how it feels.  I like how it smells.  I like the look of all that lumber lined up perfectly, although it'll get hidden.  I also like how it holds the subfloor.  The problem is, around here at least, finding good, straight, clear dimensional lumber is getting harder and harder.  I think the rapid growth plantation timber just isn't as good
Find what you love and let it kill you.

 

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