Replies

1. 
   Mad_Dog | Sep 01, 1999 09:39am | #1

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   Brent:
   Even though you did not specify your subfloor
   system, you could probably assume that the
   finished floor will not necessarily be "weak" but
   will most likely be bouncy, since the ratings are
   generally for strength/safety characteristics
   rather than comfort and practicality. For tile,
   there will probably be too much deflection,
   resulting in many problems down the road.

   I also inferred that you are not necessarily
   referring to maximum TJI spacing but rather to max
   spans. If this is correct, you can possibly take
   care of this underneath with a beam or other load
   distributing method. (Stud wall, etc.) Maybe a
   little more detail would help us here.

   Have you considered floor trusses

2. 
   Guest_ | Sep 01, 1999 09:59am | #2

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   1. TJI span sheets typically have several different tables to calculate spans. If you consider the "rated length" to be miminum code, or L/360, you will be quite diappointed in the performance of your floor system. Typically, L/480 is considered the minimum for average construction. You can go higher should you choose.

   There is an approximate 10% span reduction when going from L/360 to L/480. Thus, if an 11.875" TJI spaced 16"OC is rated for a 20' span at L/360, L/480 would require approximately an 18' span. (Numbers are estimates, I don't have a span chart handy.) You also lose about 6" of rated span when you don't glue the subfloor to the joists.

   2. If you consider code to be "spec", then yes, overspec them indeed.

1. 
   Guest_ | Sep 01, 1999 03:11pm | #3

   *Brent Your local supplier can tell you how much the deflection will be. let them look at the plans and give their recommdations for which joist to use. McMillian has a great support network that will be happy to help you. But let them tell you which joist to use. I just finnished one with tjipro 12" on 16" centers it spannet just over 21' in one place. The local rep said this was pushing it. But the follr is good and solid.

1. 
   Guest_ | Sep 01, 1999 03:55pm | #4

   *Brent, TJI's which are pushed to the limit probably aren't "weak". But they may not be very stiff, either. Keep in mind that strength and stiffness are 2 separate issues, and are only loosely related. Decreasing the spacing of your floor system will make it stronger. Increasing the depth of your floor system will make it stiffer. Mongo is dead on when he says to only use I-joists that make L/480 at the spans you want to use. But even that doesn't guarantee your floor won't feel springy. You can take long, skinny I-joists, close up the spacing, meet L/480, and still have a bouncy floor. In my experience, if the I-joists will go 24" O.C. and span as far as you want to go (according to the span charts), they probably won't feel bouncy. If you (or anyone) is interested, I can email you a spreadsheet which will predict the frequency in herz (cycles per second) that a floor will vibrate at. It's based on a formula from some research done at the Univertity of Virginia regarding floor performance. Mongo also makes a good point about glueing down you subfloor. Many span charts make allowances for this, or simply require it. Best of luck with your house.

1. 
   Guest_ | Sep 01, 1999 07:48pm | #6

   *Brent-There is a product that was in either FHB or JLC that is an engineered brace to replace blocking in floors. I believe the name was "IBS" but I could look it up. They are basically premade "X" braces that nail up inbetween your joists. They are rated to lengthen the span (or decrease deflection). They also are nice because they make it easy to run wire and plumbing down joist bays. This is not just something I've read about, I put them in a TJI floor that was nearing it's max span and they really made a difference in stiffness. Also, the manufacturer, which is in Canada I think, was extremely helpful. I'm not a huge fan of conventional blocking or bridging but I think these really work. They may help if you have limitations on depth for the floor. If you are interested, I can try to dig up the information for you.

3. 
   brent_collins | Sep 01, 1999 07:48pm | #5

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   I am in the processing of bidding out my home and have a couple of questions about the flooring.

   1. Will you have a weak floor if you span your TJI to their rated length?
   2. Will have ceramic tile on the floor. Should I over spec the TJI's?