Tile subfloor

I have removed the flooring in the kitchen to the sub floor which is 1x8" planking on 16" center 2/8" joists nailed at a 45 degree angle to the joists. I have 3/4" height to the adjoing room's hardwood floor. I want to install tile in the kitchen; can I put down 1/2" backer board on the 1/8" flooring which with the tile would get me to the 3/4" height and be stable enough?

No. The planks will move too much between seasons. A plank floor requires a minimum of 1/2" plywood on top of it, then either a membrane (thinner) or cbu (1/4" is fine), then the tile. The only other alternative is to remove the planks and put down a layer of 3/4" ply. Also, check the overall deflection of the joists to see if they are strong enough for a tile install. A good place to do that is at www.johnbridge.com. Use the "Deflecto" tool in the blue bar of the forum.

Thanks Jim, I suspected that,,,I can live with 1/2" ply with 1/4" backer, I will just put a transition guard in the door way.