My hearth is way over the R value required for my stove, Do I still need to cut away carpet?

[JPapiPE]

My Englander stove specifies an R-2 hearth. I have easily made that with the two layers of Micore 1/2" pieces stacked. In addition I have 2 layers of 1/2" Durock on top of the micore and to top this all off I have 5/16 " of tile on top of the Durock... Plus the whole system sets on top of a piece of 3/4" CDX plywood which is boxed in by 3/4" X 3-1/4" oak trim which is screwed to the plywood with drywall trim screws and makes my hearth portable. It's pretty now and i did take some photos of the framework all filled and stained. All I have to do now is drop in the micore and the durock and fasten it to the plywood base, and then i'm ready for tile and grout. I certainly must have gained an extra R- value of 1 added to my already value of R-2. I would really rather not cut the carpet as I may move soon and would like to take my stove and hearth with me. This is going to be a super fire resistant hearth, at 4'X 4'plus the oak trim and the 2 additional layers of Durock and tile I would guess this baby set me back some $275 for materials only.
Thanks all, Joe

 

[Highbeam]

No reason to cut carpet that I can see. It will pass inspection with carpet beneath the hearth here in WA. The combustible carpet is very protected beneath all of the hearth.

 

[myzamboni]

If your hearth is 4x4 do you still have the required 18" in front of the stove to meet code?

 

[JPapiPE]

My 4'x4' hearth is the size of the hearth before adding the oak trim and i do have 18" of hearth in front of the stove and 12" of hearth on the other 3 sides.

 

[thechimneysweep]

Not to worry, JP, it is a given that your hearth will stand on top of some kind of combustible material, be it floor joists, subfloor, plywood, wood flooring, linoleum or carpet. Protection of combustibles beneath the hearth is the reason for R value requirements in the first place: if your hearth has the R value the listing requires, there's no need to remove any of these materials underneath.

Now, whether a future owner of the home who doesn't want a stove will be able to unsmoosh that carpet and color-age it to match the surrounding carpet which has been exposed to air, sunlight, dirt, dust and foot traffic for X period of time is another issue....

 

[jtp10181]

We drop premade hearth pads on carpet all the time, never had a problem.

 

[brider]

Interesting...

I posted this same problem/quandry a while back, and the overwhelming respnse I got was to cut the carpeting.

My concern in that post was the possible deformation of the hearth pad and subsequent cracking because it was on a compressible surface, but I suppose if you consider the entire hearth pad stackup infinitly rigid, it should work.

I might re-consider and NOT trim the carpet after all.

 

[brider]

https://www.hearth.com/talk/threads/19363/

The above link is to the question I posted about a hearth pad over carpeting.

In my case, the minimum required Micore thickness was not too thick so maybe I was thinking in terms of a minimal-thickness pad, which MIGHT crack if you stepped on an edge.

But the current poster's proposed pad is a bit more stout than I was thinking of building, so maybe it WILL work!

 

[JPapiPE]

I have 2 layers of 1/2" micore that gives me an R value of 2 ( which is the minimum requirement for my stove hearth) Plus i have added 2 layers of 1/2' Durock over this and then finished the whole thing off with a layer of 5/16" tile. Plus I have a 3/4" layer of plywood beneath all this that ties the oak frame around the hearth together.

 

[JPapiPE]

Your have a very good point Brider. If your hearth materials are simply stacked onto a carpet without a rigid frame structure (including a rigid integral bottom and sides, all attached to each other) I think it has a good chance to crack, and be a dangerous siuation. It would fail as some parts of the hearth are moving from compression forces...such as standing on a corner of the hearth. This compression load produces a force called shear, as a point load is being presented to a section of the hearth and the resistance is not uniform (as in the deflection in the carpet) so you have a failure, i.e., a cracked hearth

However if you build a rigid box over a carpet, when you step on a corner of the hearth the whole compression force is applied to the whole hearth and shear does no occur. I think the minumum box would 3/4" plywood base and 3/4" thich sides. This method does also lend it self to a nice solid trimmed out hearth. My sides are 3-1/4" tall Oak to fit all the hearth layers into it, and the tile will come flush to the top of this box.