24" spacing on floor joists [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile

PDA

View Full Version : 24" spacing on floor joists


Loomis97
03-29-2015, 09:50 AM
I have read a lot on this subject but get conflicting answers. I have a room above my garage that I want to install tile in the concern I have is that it is a bonuse room truss on 24" centers. The span above the garage is 24' but the room itself is only 18' wide I have installed flat blocking on all the seams and sprayed 3"of closed cell spray foam underneath for added support. Basf claims that at three inches their spray foam adds 300 percent rack strength. The floor is sheeted with 3/4 t/g plywood glued and nailed to the joists in addition I have added another sheet of 1/2 glued and screwed 6" on center running across the other sheets staggering the seams by 2'. I was planning on using the ditra underlayment over the plywood. The tile we have is the wood floor type 6" x24". I have used some of the deflection calculators and they say no but they don't ask for added info on the added support. I have ran some of my own tests like filling a glass of water to the brim and jumping next to it. The water ripples but none of it spills. None of the so called tile pros around my area seem to be able to answer the question. Any help would be greatly appreciated. My question is if the floor will hold the tile without breaking tile due to deflection. Also the corner of the room sets on the exterior wall of the garage below and then goes 24' across to the other support wall

Sponsored Links


cx
03-29-2015, 10:08 AM
Welcome, JMoe. :)

The size of the room to be tiled has nothing to do with the unsupported span of the joists for purpose of determining deflection.

None of the additions you describe has helped your joist structure at all.

The only way to determine the design deflection of your joist structure is to gather the necessary dimensions and contact the manufacturer. While engineered wood floor joists are generally designed to L/480 on long spans like that, I can't guess what a builder might have used for a "bonus room." While it might be safe to presume at least L/360, I'd want more specific information on the installation before committing to ceramic tile....in addition I have added another sheet of 1/2 glued and screwed 6" on center running across the other sheets staggering the seams by 2'Am I understanding that to mean your second layer sheets are perpendicular to the first layer?

Loomis97
03-29-2015, 10:16 AM
I found the engineered truss drawings and they say meets 360 live and 240 total load on the truss t2 and on the truss t1 is says meets 240 live and 180 total load

cx
03-29-2015, 11:19 AM
Please post a link to that information, JMoe. And I can't see which of those trusses you might have from here, eh?

And how 'bout my question on the orientation of your second layer of plywood?

Loomis97
03-29-2015, 05:00 PM
I will get the info on the trusses. As for the plywood the second layer is perpendicular to the first layer with the edges of the sheets landing on the trusses with a 2' overlap on the first layer seams glued and screwed 6" o.c. The screws don't go into the trusses just the first layer of ply.

cx
03-29-2015, 05:44 PM
Sorry to be the bearer of bad news, but that means you've essentially installed a half-inch spacer rather than a second layer of subflooring, JMoe. All layers of structural subflooring must be oriented with the strength axis perpendicular to the joists.

Here is a good article (http://www.johnbridge.com/vbulletin/attachment.php?attachmentid=170333&d=1364341545) from our (Liberry) showing what I think is the very best method of installing that second layer of subflooring.

With what did you glue this second layer?

Lakee911
03-31-2015, 02:56 PM
...with a 2' overlap on the first layer seams glued and screwed 6" o.c.

What kind of glue did you use between the sheets?