Clearance - non combustible wall

[whitesjtaa]

I installed a woodstock woodstove in a corner installation with all the proper clearances from the corner walls. This was 3-4 years ago. I just built a wall behind the stove to close the corner behind it and will ultimately put in a marble mantle to create the appearance of an existing closed off fireplace behind the stove. The stovepipe down to the stove level is all insulated metalbestos rather than regular internal stovepipe as I always planned to enclose it.

The wall is made with metal studs and cementboard (the newer tan version versus the old gray version) and the clearances are less than that required for a combustable wall. The stove has a shield on the back and the wall stays pretty cool around the stove. However, the cementboard just above the horizontal stovepipe gets pretty hot over an area about 8-10 inches above the pipe. I am pretty sure that what I have created is a non-combustible surface but want to be sure. Is the new tan cementboard non-combustible? When cutting and installing it this weekend, it seemed to have a fiberous texture in the center.

Thanks

 

[jtp10181]

It is Hardibacker board?

http://www.jameshardieeu.com/pages.php?pages=products&subpage=hbacker

 

[Jay Shank]

It most likely fiberglass. the cement-board we used to install as underlayment for tile had this i believe it was called wonderboard.

jay

 

[whitesjtaa]

Yes, it is hardibacker. Thanks for the link. The website indicates the cellulose fiber is from "plantation grown Radiata Pine trees" but it also says specifically that the fibre cement material "will not burn". Says that "small amounts of other chemical additives are used to provide products with particular characteristics". Hate to think what they added, but as long as it won't burn, I think I'm okay.

If anyone can think of something I'm missing please let me know. Otherwise, thanks for the help.

Jeff

 

[begreen]

The preferred product is a pure cement board like Durock. From the Hardibacker FAQ regarding use in barbeques and fireplaces: "While Hardibacker® Backerboard is an interior non-combustible product, it is often used with barbecues. It is not a recommended or a warranted application."

This seems like a bit of double-speak, saying it's used a lot for this application, but we can't recommend or warrant it.

 

[whitesjtaa]

Well, that was helpful. Their webiste is not terribly clear or useful to state that the product "will not burn" and then not recommend it around fireplaces. Looks like I should do some work this weekend replacing the Hardibacker with Durock.

Thanks for pointing that out.

 

[Metal]

That would be the best idea. Better safe than sorry.

 

[whitesjtaa]

I noticed another thread in hearth.com on this exact topic last night. Thought I would tie it into this thread in case someone else is looking.

https://www.hearth.com/econtent/index.php/forums/viewthread/1183/

Basically, very similar confusion regarding the fire rating with an ending suggestion to use a wall thimble for a combustible wall. I don't believe I will go that far with it but I am going to switch to Durock and change my single wall stovepipe going through the Durock to a double wall stovepipe.

Thanks for all your help on this.

 

[elkimmeg]

I'm offering a different point of view Hardibacker board is 90% portland concrete

Non-Combustibility
When tested in accordance with ASTM Method E-136, HardieBacker cement board is recognized as a non-combustible building material in NER-405.

Surface Burning Characteristics
When tested in accordance with ASTM method E-84: Flame Spread – 0, Fuel Contributed – 0, Smoke Developed – 5.

Fire Rated Assemblies
Hardibacker cement board may be used as a component in one-hour fire-resistive wall construction; consult NER-405 and Intertek-ETLSemko website listings for recognized assemblies, or contact James Hardie’s Technical Services at 1-800-9HARDIE (1-800-942-7343).

 

[whitesjtaa]

I just spoke with a tech at James Hardie. He confirms that the Hardibacker is non-combustible and meets all required standards. When I pointed out the FAQ comment on their website regarding "not a recommended or a warranted application" he said that just relates to the fact that the product was developed and designed for backing in wet areas.

When I described my application, he confirmed the hardibacker product would be non-combustible. I am still going to switch to a double walled stove pipe for the pass through and perhaps increase the size of the hole for more air circulation but I believe I'll leave the hardibacker.

Thanks to all for your help.

 

[elkimmeg]

I seamed a shame to do all that work and rip it out to use wonder /durarock board when the product you used is actually better I wish you posted a picture of what you are doing so I could focus on what you are trying to do