Posted: Mar 22, 2016 9:45 pm
Backer board unfortunately adds nothing in terms of strength it is there simply to decouple the tile from the wood which have radically different expansion factors. On a floor you can use the thinnest backer board you can find. In fact you can actually use membranes such as Ditra.
Plug your particular numbers into the handy-dandy 'Deflecto' calculator on the link above and it will tell you whether or not you need more plywood or stiffer joists. You will need: joist size and span between supports, joist spacing (16" or 24" typically), joist material (likely hem/fir for your place).
Plug your particular numbers into the handy-dandy 'Deflecto' calculator on the link above and it will tell you whether or not you need more plywood or stiffer joists. You will need: joist size and span between supports, joist spacing (16" or 24" typically), joist material (likely hem/fir for your place).