Time For Another Round Of "Is It Safe?"

[PSFarms]

We're upgrading to a True North TN20 woodstove. In anticipation of the upgrade, we were donated a hearth. Since I'm a little new at this, could you folks take a look and see if you think its construction is safe? The bricks are 1/2 inch thick and the wood is 1 inch thick. Thanks for playing!!

 

[steppinthrax]

I'm very new to this (about 1 or two posts), but I did find this PDF regarding Fireplace/Chimney Code.

It calls for the following.

Hearth extensions shall be of masonry or concrete at least 2 inches (51 mm) thick and supported by noncombustible materials and reinforced to carry its own weight and all imposed loads.

So based on this it fails

 

[steppinthrax]

(broken link removed to http://www.greenwichct.org/upload/medialibrary/867/hearth.pdf)

Now I just looked at this, it's for Connecticut, but I don't see how it should differ too much.

 

[rwhite]

You need to get the manual for the stove. IF I read it correctly it needs non combustible ember protection only so technically the tile surface qualifys. The hearth pad also needs to be of a size to meet all the requirements listed in the manual. If this is a free floating hearth that will sit on carpet I doubt the 1/2" particle board would support the weight without bowing.

 

[bholler]

Hearth extensions shall be of masonry or concrete at least 2 inches (51 mm) thick and supported by noncombustible materials and reinforced to carry its own weight and all imposed loads.

Yes but that is for a hearth extension for a wood burning fireplace not a hearth for a wood stove. That requirement is set by the stove manufacturer. This manufacturer only requires ember protection. The problem I see is that the tile is just on wood. That means if there are any cracks in the grout you dont have complete ember protection. So no unless there is a sheet of metal under those tile it does not meet the requirements.

 

[rwhite]

I think that bowing and flexing would ultimately lead to cracks in grout and tiles. Your best bet is to start from scratch and put the proper tile underlayment on over the floor surface.

 

[PSFarms]

Thanks for all the great answers!! Looks like it's back to the drawing board!

 

[Sprinter]

Two bibles: local ordinances and the manufacturer's requirements.

Actually three if you count my own advice Ember protection is usually stated as 16" from the door in the US. Please add two inches, as is the standard in Canada. I've got a few melt spots in my carpet to back myself up....

 

[begreen]

You would be fine with a sheet of cement board if the budget is tight.

 

[leco]

I'll echo what others said here; You need to find out what your stove manual specifies with regard to flooring protection. It will likely say that some "R-value" is required over a space, so many inches beyond surfaces of your stove (Such as the door and sides)

I am pretty new here, but just built a hearth pad for my stove and found a few things

R-values of common hearth materials:

Ceramic Tile 1/4” 0.020
Granite 1/4” 0.020
Slate 1/4” 0.025
Cement Mortar 1/2” 0.025
Cementboard 1/4”-1/2” 0.20-0.39
Common Brick 2.25” 0.450
Common Brick 4.00” 0.800
Mineral/Ceramic Fiber Board 1/2” 1.10-1.470

Specifications for floor protectors may be listed in terms of R-value, K-value, or C-value.

To convert K or C value to R-value use the following formulas.
K to R: R=1/K x T (Thickness of the alternate material)
C to R: R=1/C

Of course the best source of information on the R value of a material, is that material's specification sheet. For instance, here is the (broken link removed to http://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/durock-cement-board-submittal-CB399.pdf). (I'm not endorsing it, I just know a lot of people use if for a pad material.) You can see on page 3, where the thermal values are listed, in both "R" and "K" values.

Basically you add up all the R values of all your non-combustible materials, between the stove, and the first combustible flooring item.

My stove required a 0.893 R-value for floor protection. I was using cement board as a primary insulating layer. Each 1/2" sheet has 0.39 R value. 2 sheets (0.78 R) was not enough, so I used three sheets. This sat on top of a plywood platform, and then had tile on top of it. It looks, layer by layer, something like this:

STOVE
(0.02 R) Tile
(0.39 R) 1/2" cement board
(0.39 R) 1/2" cement board
(0.39 R) 1/2" cement board
(combustible) Plywood
(combustible) 2x4s
(combustible) Plywood
FLOOR

Totaling up the R values between the stove and the first layer of combustibles, you see I have 1.19 of R value, which exceeds my requirement of 0.893 R.

Good luck with your hearth build.

 

[firefighterjake]

If your stove only requires ember protection I would say technically this hearth meets the requirement . . . but would I use it . . . nope? As mentioned, if there are any cracks in the grout or tile there is a chance an ember or small coal cold work its way to the wood underneath which is combustible.

Me . . . I think you have two options (assuming this existing hearth meets the size requirements for your stove).

A) Put another lay of tile or cement board over the existing tile and hope the first layer was mortared in well . . . and that the tile underneath doesn't pop off.

B) (My personal recommendation) . . . Build your own hearth. If money is a major concern you can get by with a sheet or two of cement board for now. If this is going right on top of carpet I might suggest getting a thick sheet of plywood for the base, screw down one layer of cement board and then a second layer of cement board on top of that (making sure the seams do not line up.) If you still have the time and money you can then pick out a nice tile and lay down that layer over the top . . . or simply run the stove with just the cement board on top if time and money are not available right now.

 

[CenterTree]

Two bibles: local ordinances and the manufacturer's requirements.

Actually three if you count my own advice Ember protection is usually stated as 16" from the door in the US. Please add two inches, as is the standard in Canada. I've got a few melt spots in my carpet to back myself up....

Embers in the US are not allowed to jump any farther than 16 inches,,,that's part of the rules.
Canadian embers have a little more freedom and can go the extra 2 inches. That's a fact. Hence the "rule".

 

[Sprinter]

Embers in the US are not allowed to jump any farther than 16 inches,,,that's part of the rules.

Good one.