Q: One visitor asked, "I have a 175 year old farmhouse with wide plank flooring in the kitchen. It is very uneven, as well as the foundation of the house being on a downhill slant in the kitchen. What should I use to put over the existing floor - we have considered 3/8, 5/8 or 3/4" plywood. Is this appropriate?"

A: I think that would depend what you want to accomplish by using the plywood. If you are looking for a smoother, more even surface to install a hardwood floor over, then you should be fine with 3/8 spruce plywood, screwed through the existing pine planking, into the floor joists. But this will not eliminate the slope you mention. How much of a drop is there from one end of the room to the other? If it is very severe, then you may have to either build an additional sub floor over this, or, even better, remove the sub floor that is existing, and install shims on the joists as needed to make them all the same height. In this case, you could either use the boards you have removed as your sub floor, or use 3/4 plywood.