I need some expert advice regarding floor trusses.
I just received a quote regarding a shell package. There is a 15k price difference between two lumber yards. 41k and 26k including trusses.
I don’t have any experience at understanding floor truss specs. In the past, I’ve only installed what they shipped. Now I’m going to have to explain the differences in these quotes and I’m sure some of it will be in the floor loading.
Heres my question(s).
If you were designing for an anal engineer type, what would you spec for floor loading? There will be some tile, some hardwood and some wood floor.
Please give me a quick primer on what the terms L360, L240 or whatever mean. I’ll be getting the explanation from the lumber guys, but I want to make sure I’m not getting too much bs.
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It's late in the east... Boss is probably asleep by now.
I think he does all his posting at work. Thats why they are six weeks behind.
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Watch it... I ribbed him about something like that once... he punched me out.
I'll leave it to others to answer the engineering questions, but as a guy who gets down on his knees to set tile, gimme a L/480 floor frame with 1-1/16" subfloor, if your client can afford it.
My client is interested in high end performance, but I'm not going to recomment 1 1/16'' ply unless someone can tell me why it's better. It sounds heavy and we might have to lay it.
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L/360 minimum. Basically that means that the member can deflect 1/360 of hte total span. If you have a 24' truss it can deflect up to .8" (288/360=.80).
I know the TCA specs a maximum deflection of L/360 with a #300 point load. Since you have an engineer to satisfy I would never settle for less and investigate what it would cost to step up to L/480.
Jon Blakemore
RappahannockINC.com Fredericksburg, VA
I'm not asleep yet, but am headed there.
I'll type more in the morning when I have a bit more time. I post a lot of stuff early when the jobs are downloading via email and I'm waiting on them.
Thanks Boss.
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Let's start with the loading stuff first. Typical residential floor loading around here is 40 PSF live on the top chord, 10 PSF dead load on the top chord, and 5 PSF dead load on the bottom chord. (We are talking about residential loading, aren't we?)If we know there will be tile, we add another 10 PSF dead load to the top chord. (Although I think that's overkill)Speaking of tile - I've heard it said that the floor system should always be 16" O.C. if you use tile. I assume that has something to do with possible deflection of the plywood between the joists, but don't know for sure. Maybe someone else will jump in who knows more about it. I've never seen a code that addressed this - I think the recommendation was made by a tile manufacturer..On the deflection stuff - Like Jon Blakemore said, L/360 means that something can deflect up to 1/360th of it's span. The thing that can be confusing about this is that there is a second deflection number that's implied. For instance - If you go to a truss company and specify L/360 for the floor, that's generally taken to apply to the LIVE load only. The second number that's implied is L/240 for TOTAL load deflection. (the live and dead loads combined)So in Jon Blakemore's example of a 24' truss at L/360, the design would be allowed to deflect .8" under live load, and 1.2" under the TOTAL load. That's a lot of deflection.On floors, I wouldn't suggest accepting anything less than L/480 for live load. That means .6" max live load deflection, and .8" total load deflection..If your customer is a number cruncher, he might be interested in the stuff I posted in the floor vibration thread. Here's a link if you don't have it handy:http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=21010.1.I also have the floor vibration formula in a spreadsheet that I'd be glad to email to ya. .Do you have printed quotes from both places? If you do, and want to fax them to me, I'll look them over and tell you whatever I can figure out from them. But I ain't gonna post the number here. Don't want some of these loonies to get ahold of it......(-:
If life was fair, Elvis would be alive, and all the impersonators would be dead.
Thanks for the info Boss. I don't have anything specific to share with you yet, but when I do, I'll get it to you.
I did print out that link and I'll share it with my client.
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