Hearth pad with high R value, > 3, max 2" thick, 4' x 8'

[frankm1960]

I am considering building a hearth pad for use on top of a wood construction floor. It needs to be relatively thin with a high R value. I don't have a lot of height to spare as the stove will go in front of my old fireplace.

So I'm thinking of using a sandwich construction consisting of 1.5" roxul comfort board IS and 1/2" durock.

I would lay the 4 roxul (2' x 4') sheets on right on top of the subfloor and the 4' x 8' sheet of durock on top of it.

I know the roxul comfort board is rigid but not sure how easy it compresses. I may have to include some strips of durock 1.5 wide and put them on edge between a couple sheets of roxul for support right where the stove sits. I would install a wood edge around 3 sides of the pad for edge support and to keep everything together. The back would be right up against the fireplace. I would finish it with ceramic tile.

I haven't done anything yet as I would just like to hear some feedback from the folks here first.

So, has anyone tried using roxul and durock in this way for a hearth pad and any idea of what the R value would be ?

 

[hoverwheel]

Other than building an elevated platform (my stove is short and I'm tall) and slightly different materials...

I need 1.5 R and plan to obtain that with four layers of Durock. 1/2" thick Durock (Next Gen) is 0.39 R. I'd planned to use a layer of brick to reduce costs but it wasn't worth the extra effort. All this will be tiled over.

Around here Durock comes in 3x5 sheets. If you really are getting 4x8 sheets, get a friend or two to help - they'll be heavy...

R Value list, from a thread here on Hearth.com:

https://chimneysweeponline.com/horvalue.htm

Roxul doesn't appear to be on that list. Make sure it is non-combustible or R Value or not you won't meet code or safety.

 

[xSpecBx]

Have you looked into Micore 160 or 300?

 

[frankm1960]

This is off the Roxul website.
Roxul has a melting point of around 2150deg F and is non combustible. It really should be on the list because fibreglass bats are there.

Back on topic. I found that roxul comfort board is way to unstable and for what I had in mind (see my original post) and so is durock, it's way to brittle and has very little strength unless it's installed on something real solid. It's back to the drawing board.


I have not looked into micore. HD does not sell it I'm told.

 

[begreen]

Some background is required here. Covered in this thread:
https://www.hearth.com/talk/threads/rear-flue-exit-vs-top-flue-exit.122666/