New lolly column under new tile floor?

[tvs13]

I'm going to be installing new tile floor in my kitchen but my floor at the present time is too "springy". Currently it's 3/4" T&G with 1/2" plywood and linoleum. I'll be removing the linoleum and screwing and gluing 1/4" hardibacker or wonderboard to the plywood. Now for my question. I'll sister a joist or two in the basement where possible. (Lots of penetrations for wires/plumbing etc) but I'd like to add a lolly column or two to stiffen the floor. Since these are not part of the original structure and are primarily stiffening the floor above, will it suffice just to have them sit on top of the basement slab (about 4" thick) rather than cut a hole and pour a footing? Thanks

[awesomedell]

When you start planning for a "new tile floor" you need to look at the overall framing & subfloor to determine whether or not it will meet minimum deflection rates for tile. Several factors come into play, you have to take into account the size of the of the joists (2"x8", 2"x10", etc), the spacing (16" on center, etc), the span (how far is it between supporting columns, walls) all need to be known so you can figure the deflection rate for the surface. If you will post back with this info I'd be happy to calculate the deflection rate for you and advise further. Adding support columns will decrease the span and stiffen the floor, but without knowing the other factors can't say if a tile install will hold up or not.

Other thing you mentioned that isn't proper procedure is the glue & screw of the cbu. Glue shouldn't be used, as glue will still give you some give. Instead it should be set in thinset over the plywood subfloor, which should be a minimum of 1-1/14" in thickness.

Post back with the additional info and we'll go from there.

[tvs13]

To understand this you need to draw a picture on an 81/2 x 11 piece of paper. At the bottom of the sheet draw a 2"x4" rect. horizontally. On top of that draw a 2x4 inch rect. vertically. On top of that draw anouther 2x4 rect. horizontally. You should now have a large block style letter "I" on your paper. This is the outline of my basement with each rectangle being about 12x24. Each rect. has 2x8 floor joists on 16 inch centers runnung in the 12' direction, in other words the joists in the upper and lower rects are running vertically and in the center rect they are horizontal. The lower rect is the 12'x24' area I want to tile. The floor joists in this area rest on the foundation walls except where the lower and center rect's meet. In this area they sit on a ledger strip and are nailed into quadrupled 2x10's which run horiz along the lower edge of the center rect. In the center of this area is where the most movement is along with a slight sag. The house was built in 1950 and seems to be structurally quite sound otherwise. Thanks for your patience.

Oooops I double checked after work and those sistered beams that the lower rect are tied to are 3 (not 4) 2x10's notched to 2x8's to fit onto the sill plate at each end. I guess I'll need a lolly for sure at the center of that bottom rect. where it meets the vert rect. I wish there was a way for me to draw a pic. Thanks again. T.