[opssusan]

Hi everyone and thanks in advance for your help. We want to tile our 100 sq ft (or so) kitchen -- it's on the right front half, on the second floor of our 3 story townhouse. The subfloor is 3/4" plywood on open web trusses (24" o.c.) that run side to side across the 20 foot front 2/3 of the townhouse, switching to lengthwise for the back 1/3 of the townhouse. I know that deflection can be an issue at 24" oc -- I'm hoping that I can put Ditra XL down on top of the 3/4" plywood and have enough support for the tile job. Any opinions?

 

[JazMan]

Hi Susan,

Schluter says Ditra XL will work over 3/4" ply on joists that are up to 24" o.c. I have to take their word for it since they have tested it and I trust what they say. Just remember though, those are minimum recommendations and the span between the joists should still meet the L360 maximum deflection criteria.

Then you have the trusses' deflection rating. Have you contacted the manufacturer to see what their rating is at 50/20 live load/dead load? Minimum code is L360 at 40/10 for regular flooring, so I would like to surpass that when switching to ceramic or porcelain tile.


Jaz

 

[R&D Tile]

At 24" I would add another layer of 1/2" or better plywood, then the Ditra.

 

[Gary in WA]

And not CDX. The manufacturer says: We do not insure equivalent resistance to indention or puncture". It is a wall sheathing, not for floors, full of air pockets. Use another exterior glue plywood. Be safe, GBAR

 

[R&D Tile]

Ext grade AC or BC ply.

 

[opssusan]

Thanks everyone.....but you're talking just a bit over my head. I've seen deflection calculators on other sites, but it's for joists, not trusses. Where can I find a way to calculate the "L-factor (?)" for the open web trusses I have and if the number is within the safety range can I go ahead with just putting down the DitraXL; what are dead and live loads; will I find the exterior grade ply at HD or Lowe's?