Hearth Floor and R Value

[timeuser]

Okay, I'm getting ready to build a hearth for a Englander 13nc I just picked up and it requires floor protection of at least R 2. per the manual. I've been reading everything I can find on here and elsewhere on the web and this R value stuff for a hearth is confusing with a lot of conflicting info. Anyway, it seems the consensus is that the surest thing is something like the Micore 300 board put between some layers of Durock or Wonderboard. The Micore is near impossible to find and potentially expensive when you do.

Apparently you can order it here: (broken link removed to http://www.mantelsdirect.com/Products-Accessories/Marble-Granite-Slate/MC300-Micore-Board)

There's lots of discussion of just using sandwiched dead air space with steel studs between layers of Durock. The issue is no one seems to agree anywhere on the R value of the air space. I think I'd just assume go this route as I could get all my materials locally and it'd be cheaper but calculating the R value seems iffy. Best I gather is the R value of a dead air space of at least an 1" is about R1.

What does anyone think of pouring some vermiculite in that air space with the steel studs? Seems that'd be a cheap way to definitely bring the R value to at least 2+ easily?

 

[edthedawg]

timeuser,

Here's a link to an old thread regarding R2 hearth construction on the cheap. Mebbe it'll help? Might be the thing you absolutely wanna avoid?

https://www.hearth.com/talk/threads/31683/

Only other thing I could offer would be to use firesafing mineral wool insulation. My Heritage manual claims it gives R 3.12 per inch of thickness. I can readily obtain vast quantities of it for cheap at any good building supply company (hint: NOT HD or Lowes). I used it a bunch in my recent renovation, where I needed to fireblock a bunch of floor and wall cavities. Great stuff, and easy to work with.

Hope this helps!

 

[branchburner]

Your best price on micore will not be from a stove/hearth source, but from a commercial building supply house, someone who sells things like fire safing and soundproofing for office buildings and such.

 

[Wet1]

Steel studs with two layers of Durock plus tile/stone on the top should be sufficient. If you're overly concerned about it, you can buy perlite on ebay for dirt cheap. A couple of cu ft of perlite or vermiculite will be more than enough.

 

[Wet1]

Micore is used in office cubical partitions and in sound deadening panels. If you can find a source for used office equipment, these should be very cheap.

 

[edthedawg]

I thought about that in the past. But how do you sell that line of reasoning past the Inspector? If it's marked and labeled as "Micore" then great...