Down to the annoying details - hearth pad

[Ditchmonkey]

I'm pretty close to ordering a Woodstock Fireview which we are very excited about. However, you know a project has a certain time/money threshold and there's a tipping point where that ONE MORE THING just makes the whole thing not worth it? I was almost there when I learned our current hearth pad was just a few inches too small and not the right R value to meet the specs for that stove. I stared at it for several hours last night until a plan formulated that I could live with and I wanted to run it by the knowledgeable folks here at Hearth.

My current hearth pad has a metal outer edge that encloses flat rocks set in concrete. My idea was to simply create a new hearth pad out of this old one, that is a bit larger and with better R value. It would have a 3/4 inch sheet of plywood as a base, with durock cement board on top of that, and my old hearth pad on top of the durock (and trim around the whole thing so it doesn't look like the Frankenstein of hearth pads). The part of the new hearth pad that is larger than the old hearth pad will be finished with tile or something on top of the durock.

Now here's where we get to the really annoying details. Woodstock told me the min R value for the hearth pad is .45. The R value of a durock board is .39. This site https://chimneysweeponline.com/horvalue.htm lists just about any kind of one inch rock as at least .079 so the durock + the old hearth pad should come in at over .45. BUT WHAT ABOUT THE METAL EDGE? The old hearth pad has the metal edge around it and this thin portion will not meet the .45 R value requirement. Does anyone have an opinion as to whether this small detail is going to derail the permit process? Is this something to worry about from a safety standpoint? Am I being completely ridiculous?

Thanks for you input!

 

[Poindexter]

The metal, at least in my jurisdiction, would be counted as conductive of heat and therefore not insulating. But if the metal is right outside the hearth area required to be insulated, I am golden.

So if you need 45x45 and the rock/durock part measures 45x45 with the metal band outside the required 45x45, no worries.

 

[pdxdave]

Durock at 0.39 plus the tile and two layers of thinset should put you easily over 0.45. The edge as long as it is outside the spec distances (6" sides, 16" front) is fine.