RE: R value lists of material needed

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firefighterjake

Minister of Fire
Jul 22, 2008
19,588
Unity/Bangor, Maine
Chimney sweep/co-worker is building a hearth . . . needs a listing of R values with various materials.

My only problem is I've found three separate sources -- The Chimney Sweep's page and two hearth articles all of which have great looking lists, but some of the R values vary when you compare the proverbial apples to apples (i.e. 1/2 inch of Wonderboard).

Specifically the sweep says he needs to build a hearth for an Englander requiring a R value of 2 for the hearth.

Any help on a definitive materials list or a suggested hearth building type would be welcome . . . he is working on this today. Thank you.
 
I've noted some minor discrepancies also. For cement board, the official R value is .52/ inch or .26 for a 1/2" sheet. This is straight from USG and CustomBuilding product's spec sheets. Are they going to put a layer of mineral board or micore down to reduce the amount of cement board needed?
 
At this point he is just looking for ideas . . . the idea of putting down 8 sheets of Wonderboard doesn't really appeal to him. Any suggested ideas . . . Micore? Metal studs?
 
firefighterjake said:
At this point he is just looking for ideas . . . the idea of putting down 8 sheets of Wonderboard doesn't really appeal to him. Any suggested ideas . . . Micore? Metal studs?

Yes. Both are alternatives. Use micore if the goal is a lower profile. If there is 5/8" or 3/4" micore 300 available, that would work fine with 2 layers of cement board on top.
 
From my Hearthstone Equinox stove manual..
 

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Next question . . . any idea where he could get some Micore or mineral wool insulation? Finding Micore here in Maine is nearly impossible . . . heck just finding contact info is a challenge.
 
That is in error for cement board and for Micore 300. Micore 300 is listed at 1.03 for 1/2" and Durock or Wonderboard are listed at R=.26. I suspect that list is also the source that Tom used on his site.

http://www.atlanticplywood.com/docs/300 Board Submittal Sheet.pdf
oh crap, I have the old spec sheets for Durock which list it at R=.26/ half inch. The new spec sheet posted on their website now lists it at .39/ half inch.
http://www.usg.com/rc/system-catalogs/durock-cement-board-system-guide-en-SA932.pdf
 
I just put 2 layers of 3/4" plywood, then 2 layers of 1/2 cement board and then tiled over the top. Was overkill for the Blaze King.
 
mhrischuk said:
From my Hearthstone Equinox stove manual..

Horizontal still air is the bargain there! I would think a raised hearth with a layer of sheet metal followed by a couple layers of durock would work providing the inspector is onboard.. Talking to the building inspector can save you lots of headaches and rework..

Ray
 
The problem with air is it doesn't support anything. You need structure and that structure isn't compliant.
 
mhrischuk said:
The problem with air is it doesn't support anything. You need structure and that structure isn't compliant.
OK suppose you use steel studs or lightweight steel beams instead of wood 2X lumber?

Ray
 
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