Question..I have a 3/4" wafer board?..Particle board? sub floor..which is laying on laminated joists that are 24" apart..my thoughts were to lay a 1/2" sanded underlayment to that perpendicular to sub floor..staggering any joints,now this is a very small floor just around 106 in length by 53 in width and with the 17.5 tile that's only a 3 tile by 6 tile job and not a single tile cut has to be made ..not a single one..first question with the new 1/2" underlayment it should be glued? not glued? and not screwed to the joists through the sub floor? 3/4" + 1/2" + 1-1/4 inches which is sufficient thickness if the the joists are spaced 16"..but what about if they are like mine 24" apart..I also purchased a Hardie 1/4" backer board the would give me 1-1/2" thickness..is this two much? need to know about not nailing 1/2" underlay to joists...and do I really need the Hardie Backer Board for such a small project? basically it is a kitchenette with a large fridge and an commercial grade ice cream stand that will just sit there and probably never be moved again...please help me with this thank you...SM.
Beef up the floor while you can
With 24's and chip board I would consider cutting the floor and adding purlins in between the joists and replace the floor with plywood. Then I'd go with Schluter underlayment.
This is a steel shed floor in the picture but the concept is the same, just with wood.
Then go with double 5/8 offset seams and Schluter. The floor will be thinner and stronger.
If you want to stick with what you have proposed I would glue and screw everything and hope it's not you taking it up down the road.
Really not a single cut? That's amazing.