Installing porcelain planks 6"x 36" with 11mm thickness, in main floor Living room that was previously carpeted. House is 2 story town, 13yrs old.
Room size across W 18' x Length joist span of 11.8'(below shows end of joists are sitting directly over steel support beam, directly under in room below shows ceiling joists span of 11'4"rest on steel beam) ,S.P.F. 2x8 joists, 16"oc, cross braces. According to-Deflector Cal. is L337
Subfloor is 5/8" OSB possibly T&G, some unevenness, dips and joint lipping more on large area on one side by patio door entry. No bounciness but does not feel as stiff as should be for large tile. Alot of squeaking and creaks even though applied several screws on all seems only lessened somewhat. I am now at this point.
I will add 1/2 or 5/8 plywood perpendicular. Then follow with a membrane like Ditra and then tile.
But advised now of possible Deflection L337 but I can not get to floor joist thru basement to sister any joists, as room is finished ceiling. How do i accomplish this correctly. Am I on borderline deflection or do I need to do more to fix this, other than stiffen with another layer plywood running perpendicular?
Appreciate any input, thx Jake