Poured chimney liner as hearth extension?

[Easy Livin’ 3000]

Need to extend my hearth to meet stove requirements. It needs to be level with existing pine plank over floor joists. I'd like cut into the planks and joists and frame a box with hardyboard on top and bottom, and fill the box with pourable chimney liner mix to be lightweight. Still need to figure out what to use to frame this hearth extension box. Perhaps fashion some laminated boards out of hardybacker? Needs to be fireproof and as lightweight as possible.what am I missing?

 

[bholler]

Need to extend my hearth to meet stove requirements. It needs to be level with existing pine plank over floor joists. I'd like cut into the planks and joists and frame a box with hardyboard on top and bottom, and fill the box with pourable chimney liner mix to be lightweight. Still need to figure out what to use to frame this hearth extension box. Perhaps fashion some laminated boards out of hardybacker? Needs to be fireproof and as lightweight as possible.what am I missing?

Is this infront of a fireplace? What stove is it for?

 

[Easy Livin’ 3000]

Is this infront of a fireplace? What stove is it for?

Yep. Flame Energy insert. Same required clearance as a Drolet 1800i. Only have about 6" currently. Think it requires at least 18", and pretty thick, will need to replace the floor, don't want a heavy concrete slab cantilevered out over the cellar. I can refer the exact specs when I am home.

 

[bholler]

Yep. Flame Energy insert. Same required clearance as a Drolet 1800i. Only have about 6" currently. Think it requires at least 18", and pretty thick, will need to replace the floor, don't want a heavy concrete slab cantilevered out over the cellar. I can refer the exact specs when I am home.

If it is a permenant hearth extension infront of a fireplace it needs to meet the code requirements for that. And what you are proposing is not even close.

 

[Easy Livin’ 3000]

If it is a permenant hearth extension infront of a fireplace it needs to meet the code requirements for that. And what you are proposing is not even close.

Could you refer me to the code that I can read to know what I'm missing, please? I'm willing to be creative to get a lightweight, fire-"proof" hearth extension that isn't a concrete slab that I'll have to support with posts in the middle of my tiny cellar. I probably am not explaining my concept clearly, I'll try to do a better job: imagine a prefab panel that exceeds the dimensions required in the stove manual, with hardyboard sheathing on both sides, fireproof structural framing- read: joists- (to be determined, maybe even steel, leaning toward laminated concrete board), filled with lightweight "concrete" (poured chimney liner), plugged into framed out hole I cut into the floor.

 

[begreen]

Based on the 1800i it looks like you need at least R=2.0 protection. The hearth extension depth if the hearth is lower than 4" is a surprising 29"!

The masonry hearth should be at least 4 inches (102 mm) higher than the combustible floor in front of it. If the hearth elevation is lower than 4 inches, the non-combustible (B) floor protector in front of the insert should have an R value equal or greater than 2.00 and shall extend 29 inches (737 mm) in front of the unit.

You could put some micore under a couple layers of Durock nex-gen to get that value and it wouldn't weigh too much.

 

[bholler]

Could you refer me to the code that I can read to know what I'm missing, please? I'm willing to be creative to get a lightweight, fire-"proof" hearth extension that isn't a concrete slab that I'll have to support with posts in the middle of my tiny cellar. I probably am not explaining my concept clearly, I'll try to do a better job: imagine a prefab panel that exceeds the dimensions required in the stove manual, with hardyboard sheathing on both sides, fireproof structural framing- read: joists- (to be determined, maybe even steel, leaning toward laminated concrete board), filled with lightweight "concrete" (poured chimney liner), plugged into framed out hole I cut into the floor.

 

[bholler]

When i get to my computer i will link the code for you

 

[bholler]

Based on the 1800i it looks like you need at least R=2.0 protection. The hearth extension depth if the hearth is lower than 4" is a surprising 29"!

The masonry hearth should be at least 4 inches (102 mm) higher than the combustible floor in front of it. If the hearth elevation is lower than 4 inches, the non-combustible (B) floor protector in front of the insert should have an R value equal or greater than 2.00 and shall extend 29 inches (737 mm) in front of the unit.

You could put some micore under a couple layers of Durock nex-gen to get that value and it wouldn't weigh too much.

it also says this


"The masonry fireplace must meet the mini
mum requirements found in
the building code
enforced locally, or the equivalent for a safe
installation."

Which means your hearth extension needs to comply with this code
R1003.9 Hearth and hearth extension. Masonry fireplace hearths and hearth extensions shall be constructed of concrete or masonry, supported by noncombustible materials, and reinforced to carry their own weight and all imposed loads. No combustible material shall remain against the underside of hearths and hearth extensions after construction.

R1003.9.1 Hearth thickness. The minimum thickness of fireplace hearths shall be 4 inches (102 mm).

R1003.9.2 Hearth extension thickness. The minimum thickness of hearth extensions shall be 2 inches (51 mm).

 

[begreen]

Hearth extensions for wood stoves are often just a type 2 hearth extension board. As the documentation says, they are actually non-combustible floor protectors. Cement board is a masonry product, no? And micore is a non-combustible support.

 

[bholler]

Hearth extensions for wood stoves are often just a type 2 hearth extension board. Cement board is a masonry product, no? And micore is a non-combustible support.

Yes a temporary board is fine. But if it a permanent part of the structure it needs to meet code for a hearth extension. And yes cement board would be fine but it needs to be supported by non combustible material and micore is not a suitable supporting material it is insulation.

 

[bholler]

And an extension made of poured liner material would be fine as long as it could support its own weight and all imposed loads and it was supported by non combustible materials. But if I understand correctly what was proposed would still be supported by the floor joists.

 

[begreen]

Yes a temporary board is fine. But if it a permanent part of the structure it needs to meet code for a hearth extension. And yes cement board would be fine but it needs to be supported by non combustible material and micore is not a suitable supporting material it is insulation.

Yes, the attempt to make it flush is an issue.

 

[bholler]

Yes, the attempt to make it flush is an issue.

yes