Building a hearth...does this seem reasonable?

[fishboat]

The burner has been installed & it's time to start the finish work.

The stove is a zero-clearance insert-type Bis Tradition CE. The top, bottom, both sides, & back of the unit are not an issue. The only non-combustible finishing I need to do is the hearth and facing around the unit. This will be done with Durock. The pic attached is a rough mockup and what I'll be building. The yellowish? area on top is the ceiling. Basic dimensions are 6 feet wide, about 11.5 feet on the left & 14.5 feet on the right. Vertical surfaces will be dry-stacked slate, horizontal of the hearth will be slate tile.

(broken image removed)


The hearth will be 6 feet wide & about 10 inches high. The hearth assembly I'm considering is below. It'll run around 220 pounds. It'll give me an R value of 1.56 (all the Durock, not counting the slate tile). The Durock layers will be screwed together with 1.25 inch Durock screws & Flexbond thinset. The stove manual only states the hearth must be a non-combustible surface....no R or K values given. The stove puts out a max of 55K Btu with a contiuous output in the 30-35K Btu range. What do you think...is this a sound approach?

Stove front
slate tile (0.375 inch)
0.5 inch Durock
0.5 inch Durock
0.5 inch Durock
0.5 inch Durock
0.5 inch Durock
24 ga galvanized flashing under stove & fully covering hearth area
0.5 inch Durock
6.75 inches dimensional lumber 2-by
subfloor

 

[fishboat]

thoughts anyone?

I'll be making the rounds and picking up all the various materials in a few hours.

thanks,

 

[JimWalshin845]

Sounds like it is very stealthy. Good luck with the project.

 

[nshif]

Very sound, but if there is no R value you dont need that may layers of Duroc. If its just for height go to the next size 2X

 

[Gooserider]

Hearth sounds good, since you only have to have a Non-Combustible surface, you could go to a thicker 2X on the supports, a layer of 3/4" plywood, a layer of Durock and then tile over, as that would meet the requirements. However what you are doing is certainly good and will be good "future-proofing" if you ever go to a different unit.

I don't know about the walls, as I'm not certain what is reqired to hold up your dry-stack slate, but it sounds neat.

One minor concern - I saw a mantle in your mockup, will that be wood? If so, will it be high enough to meet any clearance requirements on your insert?

Otherwise it looks great.

Gooserider

 

[fishboat]

Thanks to all for your suggestions.

One of the driving forces to have the excessive number of durock layers is that I want to have a roof-flashing ember strip installed...as well as using the flashing over the entire hearth to dissipate heat. If I install the flashing at the bottom of the stove (lift the stove & insert the flashing between the stove bottom & the 2 x 8's it's sitting on) then I have 3.5 inches of filler-space to build up to the hearth surface itself. I suppose another option would be to use larger 2x material as you suggest and make a Z ember strip to insert under the stove, go up a couple inches, and then insert between a couple layers of Durcock. Naturally I don't have a sheet metal break though I could rig something up...maybe start with a piece of heating duct and cut it up. Using larger 2x would certainly be easier than cutting & wrestling durock.

The layers were also building up the R value as a "just in case"..I find it surprising the manual says only "non-combustible" without any reference to insulating from, or dissipating heat.

The mantle will be wood & probably won't look like the pic here, but it will be at the regulation height above the stove front.

This is what it looks like so far:


(broken image removed)

(broken image removed)

 

[Gooserider]

Looks good, and "overkill never hurts" but just thought I would mention the alternatives.

Gooserider