Flooring Tile - Tile on floor and walls

Just checking if 1/2 in hardy backer board (hbb) on floor(over plywood)or and around the tub.Or should I put two 1/2 pieces on floor.Is it necessary to use any thing else, like tar paper for a moisture block.With 1/4 on the wall (over plaster board)to hold tiles.

Technically, you only need 1/4" for the floor, and 1/2" for walls, but you can use 1/2" on the floor too if you have height issues.

No tar paper needed for the floor, but you should install a plastic barrier against the studs in the tub/shower enclose, then hang the board.

Remember to install your board according to the instructions, which state to install the board in a bed of thinset AND screwed to the floor.

Do you know your floor joist sizes, spacing, and unsupported span? How thick is your plywood subfloor? I ask this because we want you to have a long lasting installation, and we need to make sure floor deflection is up to snuff.

I think the floor beams are 16 in and its 3/4 in thick plywood on floor (Won't know for sure until I rip it up).I've seen some kind of plastic in HD , Lowes,that they say apply to floor and then the HBB over that.When you say apply plastic around tub,do you mean say 6 mil plastic or something else.The walls are straight but you are saying use 1/2 on walls,but would still use 1/2 on floor.

Yes, use 1/2" for the walls and 1/4" or 1/2" for the floor.