new subfloor for tile

[wecker20]

I've ripped out the hardwood floor and the old t&g subfloor. Putting 3/4" t&g OSB down and then 1/2" backer board. I have true 2x6 joists on an 18 ft span with support beams spliting the span a max. of 6 ft. The joists are all in good shape but some are a little off and making it difficult to get the new floor flat. I thought about getting the joists as close to level as possible, lay down the OSB and shim it level. Then go into the basement and if I can't move a joist that's sitting low, sister a 2x4 to the top of the joist so the OSB sits nice and plumb. Would this be acceptable? I know some of these joist won't move as far as I need and I'd have the same problems with new ones(out of the budget too)

[pushkins]

Use the tile mortar (thinset) to help level out your problem areas. Either that or buy floor leveler and pour it on and let it set, then tile as per normal.