Replies

1. 
   Mike_Smith | Jul 30, 2001 11:37pm | #1

   *
   ... i have beam tables for 3x12 @ 23' but no joist tables....

   also you need the F(sub-b) to enter the table which is dependent on the species and grade...

   if it was #2 Doug Fir (1956 ?.. could be ...)

   say F(sub-b) 1100 and modulus of elasticity of 1.6...

   but... who know s?

   here's what you can do... load the floor with bags of material you know the weight of and observe the deflection...

   .no deflection ?... no problem..

   deflection at the design weight.. then you can't do it....all you need to test is the long span area...

   b but hey, whadda i no ?

1. 
   Mike_Maines_ | Jul 31, 2001 05:06am | #2

   *Ed, 3x12's at 16" o.c. are about the same strength as 2x12's 12" o.c. Mike's estimated values are about what I came up with. If you plug the numbers into a 40 psf floor you are almost there. If you plug the numbers into a 60 psf floor (close to your situation) you are way over. May not fall down, but at that close to the maximum allowed values it'll feel plenty bouncy. Will you be putting a tile floor on top of the gypcrete?Mike

1. 
   Steve_Wright | Jul 31, 2001 05:26pm | #3

   *To reinforce what Mike & Mike have said,Since you didn't give species and grade, take two cases:SPF with E=1.0e6 and Fb=900:11" deep joist needs to be 3.6" wide to span 22.5'Even so, at 3.6"x11", the deflection mid-span is 1.25" or 1/215.It does pass for horizontal shear stress.Doug Fir with E=1.6e6 and Fb=150011" deep joist needs to be 2.18" wide to span 22.5', so 2.5" works.But, at 2.5"x11", the deflection mid-span is 1.1" or 1/239.It also passes horizontal shear stress.There are saftey factors built into the Fb and E numbers, so your 2.5x11 joist probably won't break (unless defects are present), but deflection is a problem.Steve

1. 
   Ed_W | Jul 31, 2001 05:35pm | #4

   *Mike, I do plan on putting tile on the Gypcrete. this portion of the house is where the Kitchen is so I'm also concerned about the weight of the appliances too. Maybe I should look into another alternative to Gypcrete. I know there are some company that sell panels that the EX tubing snaps into that I can put on top of the floor which is much lighter. Thanks much for your reply.

1. 
   Mike_Maines_ | Jul 31, 2001 07:03pm | #5

   *Steve, is there any practical way to put a beam under those floor joists? That would solve the problem nicely.Mike

2. 
   Eric_M._Borgman | Jul 31, 2001 07:05pm | #6

   *Ed,If the only reason you want Gypcrete is to bed radiant heat tubes, why don't you consider mounting them under the floor deck from the basement side? There are several systems marketed for this purpose. Sunjoy also makes an electric coil mounted to a back-up sheet that you thinset & tile over. Avoid reinventing the wheel here, my friend.Eric

3. 
   Ed_W | Jul 31, 2001 10:15pm | #7

   *Eric,I was considering the Gypcrete because I already have a hydronic system in the house. I have baseboard in the basement and and radiant heat in the ceiling upstairs. I need to get additional heat in the kitchen since we are expanding it in an unseated enclosed patio area. Since my plaster ceilings are cracking I thought it would be a good time to move the heat into the floor. Electric is out of the question due to the cost to run it and the basement ceiling is plaster so I can't mount tubing under the first floor. I have been looking into a similar system that uses aluminum panels that mount on top of the floor and uses plywood sleepers.

4. 
   Michael_Ryan | Aug 03, 2001 10:08pm | #8

   *I have tiled many bathroom floors and have always followed the minimum of 1" plywood under a thinset tile floor rule of thumb. (I usually used 1.5")Does anyone know if 1/2" concrete board over 3/4 T&G plywood would be as sturdy and what are the benifits or drawbacks?ThanksMike

5. 
   Kevin_AtHome | Aug 07, 2001 12:11pm | #9

   *Ed, if it's quality ceramic or stone tile you plan to install and in a kitchen where the floor gets lots of visual review, you are probably asking for trouble with ANY lumber spanning 23 feet. Building codes use deflection limits of 1/360th of the span for maximum sag at the center of the span. Usually 1/4" stone /tile installations require deflection to be limited to 1/480th of the span or there abouts. If adding a center support is out of the question, you might be forced to consider "sistering" every joist with a steel plate or a man made lumber product that can better handle the long span. With a tile floor, err on the side of caution! LOL

6. 
   Ed_W | Aug 07, 2001 05:58pm | #10

   *Kevin, thanks for the advice. I've decided not to go with the gypcrete and go with an aluminum channel that I can mount on top of the floor which is much lighter. -Ed

2. 
   Ed_W | Aug 07, 2001 05:58pm | #11

   *
   I have a ranch that was built in 1956 with 3x12(2-1/2"x11" actual) floor joist 16"cc spanning 22-1/2 feet. This is the center portion of the house which is approx. 23 feet wide. The front and rear of the house have 2x12 floor joists but span no more than 16 feet due to support walls in the basement. I'd like to do a Gypcrete over pour which is 15lbs./sq.ft. Will the existing floor support this load? Should I call in a structural engineer or is there a "load table" for this info. I've seen load tables for 2x12's but nothing for the 3x12's since they are probably no longer available.
   -ad