Proper hearth building protocol?

[Farenheit 451]

Hey all, I’ve not gotten a ton of direction from elsewhere regarding how exactly to build my hearth for the woodstove. I went based off the owners manual for my progress hybrid and it said a base layer of plywood, a mid layer of cement board for insulation and then a top layer of whatever material. We are using stone out of the creek behind our house and put down a base of mortar and plan to grout in between. I’m not super handy but is there any reason what I’ve got going wouldn’t work? Thanks!

 

[webby3650]

I’m not familiar with the PH hearth requirements. If that’s all they require then you are doing great! Most manufacturers only require ember protection these days, with a few exceptions..

 

[FuzzyOne]

I can't comment or provide any advice on specifics. However, if this is a project you will have inspected, you should pose the question to the inspector.

I had met with my fire official prior to my install of a new chimney and insert. He provided sound advice and inspected the final install based upon the guidelines in the installation manual.

Did you check with them? Looks great BTW!

Sent from my SM-G955U using Tapatalk

 

[webby3650]

I can't comment or provide any advice on specifics. However, if this is a project you will have inspected, you should pose the question to the inspector.

I had met with my fire official prior to my install of a new chimney and insert. He provided sound advice and inspected the final install based upon the guidelines in the installation manual.

Did you check with them? Looks great BTW!

Sent from my SM-G955U using Tapatalk

If the installation is done in a manor that the manufacturers approves of, the inspector has nothing to add.

 

[Farenheit 451]

If the installation is done in a manor that the manufacturers approves of, the inspector has nothing to add.

I guess my father in law was wondering if the gaps between the Stone were too great. I didn’t see anything in the owners manual about measurement between material use where grout would go. As far as I can tell when it’s finished the way we are building it should be to manufacture specification.

 

[webby3650]

Mortar is considered part of the non-combustible surface.

 

[webby3650]

If they require ember protection only and no R-value, then there’s no worry.

 

[Farenheit 451]

If they require ember protection only and no R-value, then there’s no worry.

I’ll double check but concerning actual material thickness and R value this is all the owners manual mentions. Seems I’ve got it right, right?

 

[SpaceBus]

Wow, that will be amazing when it's done! I've started collecting ledge from around my property for future projects

 

[coaly]

I’ll double check but concerning actual material thickness and R value this is all the owners manual mentions. Seems I’ve got it right, right?

By your installation instructions you would need double cement board. (don't know the reduction of r value or if you have the optional 3.5 ash lip for reduced r) The portion of the page doesn't show the total r required.
Stone is only .08 per inch and mortar is .1 per half inch thickness.
Double 1/2 cement board would be .78, so added stone with mortar between them is over the required .80. 1 layer cement board (.39) and 2 inch of stone (.16) is only .55 r, which is below the requirement.

 

[begreen]

Yes and not just regular cement board. It would need 1" of Durock Nex Gen to meet the R=.80 spec. The river rock on top is no problem even with wide mortar joints. One issue may be having a level surface for the stove to sit on. If the rocks are quite rounded then it may be hard to have all 4 legs on a level surface. If you can place larger flat rocks where the legs will hit and keep them level that would be good.

 

[Farenheit 451]

Yes and not just regular cement board. It would need 1" of Durock Nex Gen to meet the R=.80 spec. The river rock on top is no problem even with wide mortar joints. One issue may be having a level surface for the stove to sit on. If the rocks are quite rounded then it may be hard to have all 4 legs on a level surface. If you can place larger flat rocks where the legs will hit and keep them level that would be good.

Yes the cement board was 3/4 inch however the total R value requirement takes all components used so between the board, 1 inch thick of mortar and then the rocks them selves which are between 1-2 inches and some of them larger we should be in the end zone at 0.8.

Thanks for the feedback everyone this was very helpful. I’ll definitely post pics once it’s finished!

 

[xman23]

I guess your doing all the stone layout before starting. That lets you move them around for a mix of big and small rocks. You need to get them all the same height, a little more mud under the thin ones. How about power washing them before you start.