Im building a hearth for a Quad 4300 ST and the Installation instructions for floor prtection is stated as " For US installations, it is necessary to install a floor protector of a minimum of 3/8 inch (9.5mm) thick metal clad millboard or equivalent a minimum of 16 inches (406mm) in front of glass and 8 inches (203mm) to both sides of the fuel loading door. " Im interested in the equivalent as I cant find metal clad millboard anywhere around here. Im hopeing that 2- 1/2" layers of Hardibacker over 2x4 metal studs over a 1/2" layer of Hardi will do what I need. All of this will be capped with 3" non combustable cultured stone. I am aware that the front protection now needs to be 18". Any thoughts would be helpfull. Thanks guys and gals.