# How much cement board under wood stove?



## SSSS (Apr 3, 2011)

I will be installing Durock cement board under a wood stove (that I don't have yet -being installed by a contractor). I would like to know if anyone knows what the international building code specifies for the thickness that this cement board needs to be? I will install porcelain tile in thinset mortar above the cement board. Thank you for any suggestions on this.


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## nate379 (Apr 3, 2011)

Depends on what stove.


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## Mt Ski Bum (Apr 3, 2011)

SSSS said:
			
		

> I will be installing Durock cement board under a wood stove (that I don't have yet -being installed by a contractor). I would like to know if anyone knows what the international building code specifies for the thickness that this cement board needs to be? I will install porcelain tile in thinset mortar above the cement board. Thank you for any suggestions on this.



the amount of insulation needed (it's R-value) for a hearth pad depends on the stove. Some stove only need ember-protection, while other stove models require much more insulation. Check your wood stove's manual to see how much insulation is required for your stove (if you know what stove you're getting, but don't have it yet, you can probably find the stove's manual online- many stove companies post the manuals for their stoves on their website)


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## fossil (Apr 3, 2011)

It's the R-value (insulative quality) of the hearth that's important.  This comes from the stove manufacturer's installation documentation.  You need to select a stove first, then build to those requirements.  Some stoves are available which require nothing more than non-combustible ember protection beneath them, while other stoves require much more in terms of the insulative property of the hearth.  You need to begin stove selection, keeping this in mind.  Don't get into building a hearth until you know what stove's gonna be sitting atop it.  Rick


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## begreen (Apr 3, 2011)

+1 Building code doesn't specify the insulative value of the hearth. The manufacturer is the one that pays to have this tested and specifies it in the stove's installation manual.

What stove is this?


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## SSSS (Apr 3, 2011)

Thank you. I don't have the stove yet and cannot find the manual online (I sent them and email asking for specs). It is a Buck Stove E85. I will try to find out. Would anyone happen to know what R value the Durock cement board or cement board in general has? I have a spec sheet from them but it doesn't note what the R value is as far as I can tell (the only info is in section 3.6 here) : http://www.westsidebmc.com/Files/Cache/file_151715.pdf?time=634373452482239889 It seems odd to me to stack layers of cement board on top of each other : /


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## begreen (Apr 3, 2011)

Most cement boards are rated at R = .52/inch. Stacking cement board to build up R value is not uncommon. If the hearth requirements are high, there other alternatives, like adding a bottom Micore layer or air space.  I'm not familiar with the Buck E85 and also don't have docs for it, but here is where their manuals reside: 
http://www.buckstove.com/stovemanuals.html

Contact Buck and ask them for the manual and tell them to post it on their site.


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## fossil (Apr 3, 2011)

SSSS said:
			
		

> Thank you. I don't have the stove yet and cannot find the manual online (I sent them and email asking for specs). It is a Buck Stove E85. I will try to find out. Would anyone happen to know what R value the Durock cement board or cement board in general has? I have a spec sheet from them but it doesn't note what the R value is as far as I can tell (the only info is in section 3.6 here) : http://www.westsidebmc.com/Files/Cache/file_151715.pdf?time=634373452482239889 It seems odd to me to stack layers of cement board on top of each other : /



Maybe you were reading a bit impatiently.  They list the R-value for a 1/2" layer of Durock as being 0.26 in the first part of the link you posted.  It's actually not at all odd to stack layers of Durock, if that's what you choose to do.  Lots of wood stoves are safely burning out there on multiple layers of cement board.  However you choose to build the hearth, and whatever materials you choose to use, the single most important consideration must be the safety of the installation, and that all starts with the stove manufacturer's requirements.  Rick


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## SSSS (Apr 3, 2011)

Thank you begreen and fossil. I did miss that. I will check the manufacturer's requirements and stack the cement board as necessary or look into the micor. I appreciate your help very much. Thank you.


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## Mt Ski Bum (Apr 3, 2011)

Here's the manual for the Buck Model 85

btw- off topic, but whats up with the stove manual saying that pine creates more creosote??  A stove company should know not to buy into that old myth...


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