need advice on adequate support for hearth install

[UPswede]

I am preparing for a new stove install on the far end wall in the main floor LR of my ranch style home and have questions about building a flush (or nearly flush) 48" W x 52" deep porcelain tile hearth. The ember-protection stove has the pedestal option and all clearance to combustibles and floor protection dimensions will be exceeded.

My concern is if I will have adequate support under the 1/4" tiles to prevent flexing and cracking.

Will this work? I have 3/4" T&G plywood on 2x10 joists spaced 16" apart (metal cross-bridged). The joist span is about 14 ft. On top of the plywood I was thinking thinset / 1/4" hardiebacker / thinset / and then 1/4" porcelain tiles.

Thought I would give the floor some additional support by building two stud walls extending from the concrete basement floor up to the bottom of the 2x10 joists (each 2x4 stud/support wall would extend out from the foundation end wall about 34 inches). The two short stud/floor support walls in the basement would reinforce 3 joists midspan and be under the stove (stub walls about 30 in. apart). By putting in two walls I can incorporate some shelving between the walls for storage purposes in the basement. Thought I could install 2x10 blocking between the joists if needed to provide additional stiffening.

Comments and ideas on how to do this easier and/or better are appreciated.

 

[Simonkenton]

With 2x10 joists 16 inch OC spanning 14 feet you are probably up to spec on subfloor support, even for a heavy wood stove installation. But, you are like me, better safe than sorry, I would go ahead and build the little wall in the basement to provide additional support.
However 3/4 inch of plywood is inadequate for a tile intall, you need to add 1/2 inch sheet of plywood to that to get up to spec. You need to put construction adhesive between the 2 sheets of plywood, and screw the top sheet of plywood into the joists with 3 1/2 inch decking screws.

 

[UPswede]

Thanks for your reply. I was hopeful that the fact that it is tongue and groove plywood might be sufficient with the additional floor support. Would that make any difference? (T&G)

 

[begreen]

He is correct. You want to avoid flexing. There is no need to put thinset down between the plywood and the backer board. Note that 1/2" Durock NexGen will provide greater insulation protection and more stiffness.

 

[UPswede]

SK and BG
Good to know. Thanks

 

[srbellis]

Don't use hardieboard. USE DUROCK