# Fireplace Insert Raised off the Slab



## Hambone (Apr 4, 2007)

Cross posting from Masonry as we are still in the 'rough-in' stage and seems quite a bit of knowledge here ....

I am the GC (home addition) and am getting ready to install an insert fireplace. The Homeowner wants the insert to sit off the floor so that a sitting bench can be accomplished. The insert has the front opening and a side opening - kind of a corner fireplace. I plan to sit the insert on a few cinder blocks to elevate it off the slab - the question I have is related to how best accomodate the sitting bench that will be on the front of the fireplace and 1 side (wraps around). 

Thinking so far about mortering the cinder block to the slab - then laying the sitting bench on the blocks - hanging over far enough for the sitting bench effect. Then attaching the insert fireplace to the sitting bench.

Can I make the sitting bench out of say plywood or some other easily workable material - then cover it with brick pavers or stucco? Any other ideas come to mind? Since the "bench" will extend 18" or so from the cinder blocks it is sitting on with no supports - I am not sure what the best way is to do this. Obviously need something strong here.

Thought of using a large slab of stone/granite to sit atop the cinder blocks - but I need something pretty thick and the HO would like to put brick pavers or stucco over the material in order to bring the hight of the "bench" up to the floor level of the fireplace. So not sure using Granite/stone is the best option.


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## georgia dawg (Aug 12, 2005)

All my inserts go into wood frames for the surround and hearth(mostly 2x4s) and then apply OSB sheathing (rough side out) covered with lathe to set up for rockwork, I use lightweight cultured stone for the surround and fieldstone for the hearth, but any rock or brick material should do. My inserts are zero clearance, but be sure to follow your insert mfgers instructions for setbacks (sides/top/etc.) and proper installation.

FYI- I start off by framing up a platform for the insert and then rough-in its opening and then build up the surround. When I get to the hearth last I just make framed boxes and attach them to the surround. (Hint: If your insert has a removable bottom panel(sometimes for a blower), be sure to lower your hearth enough so that the addition of top hearth rockwork won't "seal" in the panel. Been there, done that. To adjust for this, I got in the habit of sitting my inserts on 2x4s on top of my platform and adjusting the rough in accordingly. That way, I don't have to remember to adjust my hearth for rockwork. However, either raising the rough-in or lowering the hearth will accomdate for the rockwork.


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## Hambone (Apr 4, 2007)

*Thanks*

Georgia Dawg - thanks. I like the idea of putting it on a 2x4 platform. And thanks for all the tips you provided!!


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## hrscammisa (Mar 9, 2007)

You need to be vary careful. 2x4 and ply wd dont get it any more. My partner just got back from a class in reno nv the heat can break down the ply. that can be a start but you might need some dura rock down better check all the specks first or call the manifactor to be sure. By the way after the secind day he left the class. The liabilty was to great.


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## petermichael (Apr 13, 2007)

*Dawg is correct*

The manufacturer performs many tests on every variety of installation. The installation manual included with the fireplace will have EXACT specs on what you can and cant do. Thousands of fireplaces are installed on plywood every year with no problems when done properly. 

The main issue with any metal box fireplace is the face of the unit. The unit is engineered to push all heat out towards the face, and eliminate as much as possible everywhere else. It is for this reason that there are very critical & specific mantle and hearth requirements for all. Plywood, sheetrock, and any other material that is considered "combustible" is usually forbidden, especially on the hearth of a wood burning unit, but as I mention above, the installation manual goes into great length providing you all the information you will need.

A fireplace _insert_ is a fireplace unit that is installed into an existing fireplace. From what you are describing, it sounds like you are putting in a zero clearance fireplace, not an insert? Also, is the unit a wood or gas unit?


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## Hambone (Apr 4, 2007)

*Wood Burning Gas Unit*

Thanks for the information. The unit is a zero clearnance unit and it is wood burning with a gas connection. i.e., use the gas to start the wood then turn the gas off .... or hook up gas logs and forget the wood.


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## petermichael (Apr 13, 2007)

*Yeah*

I figured you'd say that. 

Very critical hearth requirements!


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## keepitstraight (Nov 12, 2006)

even for zero clearance i always go at least 1/2 inch minimum. make sure your fireplace guy doesn't have someone screw up the pipe clearance later, hopefully they will frame the firestops too so then nobody will get too close. not sure the clearance with double wall gas pipe but for wood some pipes require up to 12 inches of clearance from combustible materials and a firestop (one hour here, ibc 2007) of 5/8 min firestop drywall.

great points georgia. i think my brain has died tonight and there is only residue of coffee, 'night all.


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