Raised Hearth Materials

[Str8781]

When building a raised hearth out of foundation blocks, what non-combustable material is best to set between the foundation block and floor of a zero-clearance fireplace? Mainly, I'm worried about the possibility of 500+ pounds of constant pressure affecting/warping a cement board or other material.

 

[begreen]

I'm not sure what the question is about. If a couple layers of cement board are well supported, they won't warp. We see several installations built this way with just four stove legs on the hearth. A ZC fireplace usually is flat on the bottom, distributing the load evenly over a large area. For that reason, the cement blocks seem overkill here, but I may be missing something. Is your concern about putting cement board under or over the cement blocks? Which ZC fireplace? What are the R-Value (or K-value) hearth requirements for the stove?

 

[mranum]

I just had a ZC fireplace put in but I didn't need any special cement board or anything even fireproof. It could sit right on combustables. There is a heat sheild and air space below the firebox. Here is how we built ours, its a 12" high platform. We used 2x4's layered with 1/2" OSB to make a height of 5" then put 2x6's on edge on top of that. We spaced the 2x6's evenly except in the opening you see below, that was to make room for the outside air tube. Its built to support way more than our burner weighs.

Hope it helps.

 

[trailblaze]

i would think you'll be ok with 3/4 plywood, then 1-2, maybe 3 layers of Durock depending on the fireplaces R value needed...

just keep the blocks close to evenly support the plywood