You are reading a single comment by @Tenderloin and its replies.
Click here to read the full conversation.
-
I think the suggestion is about right. You want one consistent sub-floor which won't flex or contract differently and it will allow you to improve the thermal efficiency. It would also give you the opportunity to re-route any pipes or services at the same time. Alternative would be to overboard the original floor boards and build things up that way but wouldn't seem the best option.
Tenderloin
1 = original floor boards
2 = OSB boards in the extension
3 = ply that was on top of the floor which was tiled