evening, we are thinking of having a solid hardwood floor(oak) over our proposed new UFH which is between joist with a dry mix covering the pipes up to the top of the joists.The joist c-to-c are 400 mm.The UFH supplier and wood flooring suppliers are a bit vague about the following ..Can the hardwood be secret nailed straight on to the joists?With no other material between?. If so is there a minimum thickness of board and is there a maximum width that we should be looking at? Any other major pitfalls we should watch out for?Any advice welcome, thanks