Here's the deal, I have found and Avalon 996 "extended" insert for $500. I finally found a manual online and it calls for 18" of floor protection and no r value is mentioned. Beings that this is an older stove I worried that specifications may have gotten more stringent since 1990. So I looked at a manual for a Avalon Rainier. It calls for 1/4" noncombustible floor protection with a k value of .72. If my math is correct this equates to an r value of .33 (.25 (thickness)/.72 = .328) Does this look correct? I just worry that specs on the 996 may be out of date and I should build floor protecttion that is a better than called for.