Hearth pad values

[loneeagle15]

Ok I am about to start making my hearth and tileing the surrounding floor area mysub floor is wood so I need to put down the fiber board before putting down the tile and cement board under my stove. I was looiing at the r values chart and are listing thesame values for cement board and backer board am I reading this correctly? Also myunderstanding is if I use cement board and need a r value of 1.01 then I need to have 2" of cement baord am I fiqureing this out correctly?
Thank you
You guys are great
JD

 

[babalu87]

1/2" Micore + 1/2" cement board = More than enough r-value if you only need 1.01
The you can tile and grout

 

[webbie]

Cement board is sometimes also called tile back board. It is one and the same product. Bab mentions micore, which I have no experience with but has a good value......in many cases it is easier to build up 3 or 4 layers of cement board.

Yes, according to :
https://www.hearth.com/articles/64_0_1_0_M1.html

You would need 4+ layers of this board to have your value.
The Micore would MORE than do it. Perhaps some folks here can help you with a source.

Some stoves have an optional bottom heat shield which cuts the hearth requirements. Also, the tile or brick you are gonna put on top counts.

Although it is not in the chart, it is well known (and documented by NFPA) that a sheet of sheet metal below or in-between the layers adds vastly to the radiation deflection.

Can't find my NFPA stuff right now, but it does contain some generic setups.

 

[Gooserider]

Micore is hard to find, but it is definitely the solution if you need a high R-value hearth, and want to keep the thickness down. It is hard to find, but if you look hard it is available. (broken link removed) MAY help you find a source.

The other things to keep in mind are

1. Micore is fairly soft and squishy stuff, so you probably want at least a thin layer of Durock or other hard cement board between it and the tiles.
2. You don't need a ton of fasteners to hold it down, the stove does a good job of anchoring %-P Also, at least in theory, the fasteners can act as conductors of heat into the combustibles, so it is best to use short fasteners to attach each layer to only the layer under it, and stagger them. That way there is no direct path for heat to travel through the pad. It also is good to minimize the number of fasteners directly under the stove, they are mostly just needed around the edge anyways.

Gooserider

 

[Highbeam]

I am also trying to constuct a hearth with a R-1.2 value and that leaves me with 6 layers of cement board or? The micore stuff is as rare as hens teeth though if you can find it, it would be ideal. Remember that each layer of 1/2" durock is going to be pretty heavy.

 

[elkimmeg]

Micore is simmilar to ceiling tiles try looking at ceiling tiles r ratings and combustiability and burn characteristics smoke spread rating

 

[rdrcr56]

I found micor for my pad at an acoustical ceiling supply house in Denver. The pad I made is portable, 3/4 plywood, micor, cement board, micor, cement board than tile. If we move and the people that buy the house don't want the stove the pad goes with us.

 

[colsmith]

As I just posted in another thread, if you want to find Micore, ask to speak with a stove installer. The regular salespeople at stove stores might not know squat about it since it isn't officially for sale. But the place you buy your stove would probably sell you a sheet of Micore if they already use that themselves when they build hearths for customers, which they often do. Or you can go with all the sheets of cement board, but that seemed a pain in terms of height (we tiled the sides of our hearth material as well.)

 

[dstapl]

These postings are quite old, are there any updates or new experiences for using Micore and perhaps Durock under tile for a woodstove hearth? I have one update and that is USGypsum no longer recommends Durock under a hearth - their latest version (NexGen) isn't rated for this application, although earlier versions are satisfactory.

At this point I'm mostly concerned about
(1) the success of layering Micore ('soft and squishy') under cemetboard to provide a durable hearth and
(2) what might substitute for Durock as a cement board underlayment for tile

Dan

 

[DanCorcoran]

As I posted on another thread, Imperial Group of Canada sells a "stove board" in different dimensions. I bought mine for $43 at Lowe's (end-of-season clearance; normally $56) in 36" x 48". It is 1/2" of insulating material covered on top and sides with black sheet metal. On the back of the board is printed "USG Micore", so it isn't at all hard to find, if one of their dimensions fits your needs. My wood stove store sells the same pads for somewhat more money. The 1/2" Micore is R= 1.1 according to the charts I've seen. The Micore does seem pretty flexible, though, so you may want to put something stiffer under it (or above it, if your stiffener is fireproof).

 

[Gooserider]

As I posted on another thread, Imperial Group of Canada sells a "stove board" in different dimensions. I bought mine for $43 at Lowe's (end-of-season clearance; normally $56) in 36" x 48". It is 1/2" of insulating material covered on top and sides with black sheet metal. On the back of the board is printed "USG Micore", so it isn't at all hard to find, if one of their dimensions fits your needs. My wood stove store sells the same pads for somewhat more money. The 1/2" Micore is R= 1.1 according to the charts I've seen. The Micore does seem pretty flexible, though, so you may want to put something stiffer under it (or above it, if your stiffener is fireproof).

Slightly different application Dan... Although your board might be a useful approach to solving the same problem... Essentially the earlier messages are from the situation where people are wanting to build a permanent custom hearth application, where your board is more intended to be a "quick and dirty" solution of drop the board on the floor and stick a stove on it... Nothing "wrong" with that idea, but some folks want something fancier, or have a situation like I had where the existing hearth wasn't the right size and shape to put the new stove on, and I needed to extend it in a "permanent" way (code won't buy off on a removable extension) that was reasonably aesthetic...

The challenge in many of these cases can be to build up a hearth pad that has the required R-value for thermal protection of the underlying structure, but isn't so thick as to be a problem... Micore was a desirable approach because it gave a high R-value in a thin sheet. However since Micore is slightly flexible, it was usually recommended to sandwich it with a layer of cement board in order to get the rigidity that you'd want to have when covering it with stone or tile. Generally though, the challenge was to find the Micore from a local source

That said, it might be possible to "bury" a board like yours instead of a plain sheet of Micore, and get the same thermal advantage, with the advantage of possibly easier sourcing.

What might be more of a concern is the other Dan's post saying that the newer version of Durock was no longer approved for use, as there wasn't any other approved cement board type product I was able to find when I did my hearth extension a couple of years back... I don't know what to suggest.

Gooserider

 

[begreen]

Yes, this is a little disconcerting. USG appears to be muddling the issue badly. The installation guide in the link provided has wall shielding incorrect. They only are using 1/2 durock furring strips and no air gap top or bottom. This is quite different from the excellent instructions they had for 1st gen durock.

 

[Gooserider]

As I posted on another thread, Imperial Group of Canada sells a "stove board" in different dimensions. I bought mine for $43 at Lowe's (end-of-season clearance; normally $56) in 36" x 48". It is 1/2" of insulating material covered on top and sides with black sheet metal. On the back of the board is printed "USG Micore", so it isn't at all hard to find, if one of their dimensions fits your needs. My wood stove store sells the same pads for somewhat more money. The 1/2" Micore is R= 1.1 according to the charts I've seen. The Micore does seem pretty flexible, though, so you may want to put something stiffer under it (or above it, if your stiffener is fireproof).

Slightly different application Dan... Although your board might be a useful approach to solving the same problem... Essentially the earlier messages are from the situation where people are wanting to build a permanent custom hearth application, where your board is more intended to be a "quick and dirty" solution of drop the board on the floor and stick a stove on it... Nothing "wrong" with that idea, but some folks want something fancier, or have a situation like I had where the existing hearth wasn't the right size and shape to put the new stove on, and I needed to extend it in a "permanent" way (code won't buy off on a removable extension) that was reasonably aesthetic...

The challenge in many of these cases can be to build up a hearth pad that has the required R-value for thermal protection of the underlying structure, but isn't so thick as to be a problem... Micore was a desirable approach because it gave a high R-value in a thin sheet. However since Micore is slightly flexible, it was usually recommended to sandwich it with a layer of cement board in order to get the rigidity that you'd want to have when covering it with stone or tile. Generally though, the challenge was to find the Micore from a local source

That said, it might be possible to "bury" a board like yours instead of a plain sheet of Micore, and get the same thermal advantage, with the advantage of possibly easier sourcing.

What might be more of a concern is the other Dan's post saying that the newer version of Durock was no longer approved for use, as there wasn't any other approved cement board type product I was able to find when I did my hearth extension a couple of years back... I don't know what to suggest.

Gooserider

I just wanted to confirm that Durock Next Gen is suitable for use as a floor protector. I downloaded the data sheet from their website and it cleary states "Can be used as a heat shield and floor protector".
Anyone interested can follow this link to their website and then click on data sheet under the next gen name.

(broken link removed to http://www.cgcinc.com/home.asp?nav=156&mkt=30&bc=1.48.156)

I agree. I'm not a code enforcer, but it certainly would look to me like the product would work for floor protection, and since it's pretty much intended to be covered by tile or equivalent, I don't see why it wouldn't work - Dantheman, can you provide any further information as to why you said it wasn't approved?

I don't see anything in the specs given that would suggest that it would not work - the R-value looks about like the old stuff, it's billed as non-combustible, and so on...

Gooserider

 

[begreen]

Here is the proper document for wall shields and hearth. Note it is a 2007 1st gen durock document that they are referencing in the later doc.
(broken link removed to http://www.usg.com/rc/data-submittal-sheets/panels/durock/durock-cement-board-submittal-CB198.pdf)

 

[dstapl]

I see the "heat shield" reference but I've read and was told today by someone at USGypsum that NextGen is NOT rated or aproved for used as hearth material.
On a Hearth.com posting by "Inferno" on Feb 27th last year, it said
"For anyone who cares: The new version of Durock is NOT rated for hearth use. The formula they now use includes foam beads. The beads can outgas during prolonged heat exposure. The old stuff was good. The new stuff is not (for hearth use)."

 

[begreen]

Sux.

 

[Gooserider]

OK, that makes sense - I remember encountering another version of cement board that had the foam beads in it back when I was dong my hearth extension project, and getting the same answer from that manufacturer at the time...

Now of course, the question should be whether or not one can get the old generation stuff, or if there IS an approved alternative...

Gooserider

 

[DanCorcoran]

Actually, I'm using the Micore stove board as a base, then using furnace cement to glue ceramic tiles to the (scuffed) metal surface, then gluing oak moulding strips around the whole thing as a finish. I'll take photos, when (and if ever) the stove is installed. I bought the stove on December 30, and March 30 is the third time I've scheduled installation. Snow and ice on the road to the cabin are creating an ongoing problem (but that's the flip side to having a nice, isolated location!)

 

[NH_Wood]

Question: is the r-value requirement mainly for if a burning coal or log leaves the stove and lands on the pad, or is it because of the heat given off from the stove? I just built a hearthpad for my new Hearthstone Mansfield - built on upright 2/4's, 3/4" plywood, 1/2" cement board, and tile. I just can't see how the stove heat could ingnite material under the tile and 1/2" cement board - especially with the ash ban buffer in place, but now I'm a little worried. How hot would the plywood have to get before it ignited? It would seem that the heat from the bottom of the stove would have to be INTENSE to cause the plywood to burn.......any thoughts? Cheers!

 

[begreen]

Hearth requirements vary with stove construction. Some stoves just need ember protection and others need much greater insulation. It depends on the requirements set by the stove manufacturer for that model stove. Follow the manual's guidance here.

 

[dstapl]

Hearthstone recommends both Wonderboard and Durock in their wood stove installation manuals (available on line - Woodstock manuals also online), allowing an R-value of 0.2 per 1/2." We know now that Durock's "NextGen" is no longer rated for this purpose (I got that verbally from USGypsum yesterday (although they said some of their old product is still probably out there as this is a recent change) but Wonderboard's technical department ("Custom Building Products, Inc") told me today that their product has not changed. So since Hearthstone recommended Wonderboard in their manual, that should still stand.

At this point, I plan to sandwich two layers of Micore (probably Micore 300 as their Micore 160 seems to be only a lighter weight) under two layers of Wonderboard (plus tile) to give me the R 2.5 that Hearthstone says I need. This all sits on top of my 2.5" concrete slab hearth on top of a hardwood floor. I'll tie in a different 'sandwich' (extension) in front of the existing concrete hearth for the projection in front of the stove and door.

Hearthstone (and others) make the point that the heat shielding in not just for loose embers flying around; it is primarily for the heat given off by the stove and the need to protect combustible objects underneath or beyond. Different stove mfgrs and their different models all have different heat shielding requirements.

I too have a log home (in Haymarket, VA) and plan to install a Hearthstone Homestead stove on a fireplace hearth. The hearth is odd shaped (90" x 24") and I need to (1) improve the existing hearth's r-factor and extend it to provide the proper protection (16", now 18" from the stove door, etc.). You'd think either the dealer or their recommended installer would find all this out for me but I'm left to dig for the details myself.

 

[Gooserider]

Question: is the r-value requirement mainly for if a burning coal or log leaves the stove and lands on the pad, or is it because of the heat given off from the stove? I just built a hearthpad for my new Hearthstone Mansfield - built on upright 2/4's, 3/4" plywood, 1/2" cement board, and tile. I just can't see how the stove heat could ingnite material under the tile and 1/2" cement board - especially with the ash ban buffer in place, but now I'm a little worried. How hot would the plywood have to get before it ignited? It would seem that the heat from the bottom of the stove would have to be INTENSE to cause the plywood to burn.......any thoughts? Cheers!

It is mostly to deal with the heat put out by the stove, as simply having a non-combustible surface would be sufficient to deal with the occasional coal or burning log... The problem is that prolonged heating of wood at even relatively low temperatures can cause chemical changes in the wood that drastically lower it's ignition temperature - we are talking in terms of cooking the wood for years in some cases, not just a few hours, as this is a very slow process.

I forget the exact numbers, but I think the NFPA standards say that the combustibles under a hearth, or on the wall next to a stove are not allowed to reach a temperature more than 50°F above ambient, or something in that range... Essentially the manufacturer clearance values are set by burning the stove on a very carefully instrumented hearth setup with movable walls, and then pushing the walls in until they reach the critical temperature. They do a similar deal with the hearth floor to determine how much protection they need there.

Gooserider

 

[madison]

Pasted below is text from the Mansfield manual: do you actually need any R value for the Mansfield? or just non combustionable surface?
///////////////////////////////////////////
HEARTH REQUIREMENTS AND FLOOR
PROTECTION
If the floor is wood or other combustible flooring, the
stove must be placed on non-combustible floor protection
that extends 16 inches to the front and 8 inches to either
side of the front door opening.
The unit must be placed on a *non-combustible floor
protector that extends 16” in front and 6” to each side of
the unit. If installed in an alcove at reduced clearances
with NFPA 211 wall protection, the area in front of the
unit must have an additional insulative R-value of .8, or a
listed floor protection must be used.
The floor protector for the stove must have minimum
dimensions of 34-1/2” x 46” (876 x 1168 mm) and must
be placed as illustrated here:

*An example of a non-combustible floor protector would
be a hearth constructed with a continuous layer of a listed
backer board (such as Wonder-Board or Durock) used for
ember protection with a tile, brick, slate, or another nooncombustible
facing.

 

[DanCorcoran]

My Hearthstone Shelburne requires a 36" x 48" minimum pad with an R=0.8, without mentioning anything about alcove installation, so they're all different.

 

[Gooserider]

Pasted below is text from the Mansfield manual: do you actually need any R value for the Mansfield? or just non combustionable surface?
///////////////////////////////////////////
HEARTH REQUIREMENTS AND FLOOR
PROTECTION
<snip>

My reading is that as long as you aren't going into an alcove, then all you need for a Mansfield is a non-combustible surface. However as noted, there is a lot of variation, between stoves, so you need to check the exact model that you are wondering about. This can make life very frustrating for a person that is wanting to do a built in hearth that is relatively "future proof" against the requirements of any future upgrades...

There is no really good answer, but the best suggestion I can make if building from scratch, is to put as much insulation value into it as you practically can w/o extreme effort, especially if you can get over a 0.8 R-value, as that seems to cover MOST installs. If you are extending an existing hearth, make your best estimate of the existing value, and try to match it - not much point in trying to go higher, as you'd be needing to replace everything if you needed to upgrade the original hearth anyway...

Gooserider