putting ply then under floor heating then tile help?

[Phil_h]

Putting in warmup underfloor heating in and then getting it tiled.

When we put 12mm plywood down on to top of floor boards how do I screw this down....

What size screws should I use ?

What spacing do I need need between screws?

thanks.

 

[gcol]

This is covered in the tiling sticky under "Timber floors".