Designing Kitchens and Bathrooms - Replacing Bathroom Subfloor?

I am remodeling a bathroom and the subfloor is made up of what looks to be 1"x7" slats. Some of these are pretty loose or cracked.

I will be laying a tile floor. Can I just put concrete backer board over the slats and then lay the tile or do I need to remove the slats, install exterior grade plywood and then the backerboard?

If I need to remove the slats - how do I go about this. I am not sure if the edge of the floor falls on joists or not and want to make sure if I cut the slats out around the edge of the room that the edge of the new subfloor will be strong.

I have gutted the entire bathroom.

Thanks for any help.

What you are looking at are angled 1x6 or 1x8 subflooring. My house was built in 1978 and has this method. It seems to be quite good, since the slats are on an angle bias to the joisting. If there is no rot or other damage to the "slats", don't remove them. Go ahead and calculate the height you will need to build up the floor to meet the existing floor at the bathroom door. If the remaining height is 1/2 or less, then apply the backer board directly to the subflooring using the screws made for this application and spaced as the instructions stipulate. If you need to build it up, of course you can use the appropriately sized plywood to add to your subflooring, then the backer. Your floor will be just fine.

It would be best to lay down a layer of 1/2 inch plywood (don't screw into the joists), then your cbu. Without the ply there is too much movement in the subfloor. movement=cracks and a failed install.

Make sure when you install your cbu you set it in thinset.

You can not put backer over that plank subfloor. This type of wood has way to much movement, expansion contraction. You must put at least 1/2" ply over the planks. Use an exterior grade plywood bc or better. Face grain must be pependicular to the joists. Use an unmodified thinset between the ply and the backerboard.