hearth extension questions

[napoleon1101]

Hi everyone,

I'm new to the forum and have a question regarding my hearth extension that I'm building. This is to acomadate a napoleon 1101 insert and to future proof for an upgraded insert later in life. I have heard this insert puts out a lot of heat in front of it.

My existing hearth is a concrete slab that is poured in a wedge shape and part of the foundation.

I have cut out an extended area in front of the hearth and removed 3/4" of hardwood and am down to 3/4" floor boards that sit on joists. The plan was to put down 1/2" of micore, 1/4" of wonder board, then lay new tile over the entire hearth.

I am concerned about the r and k value at the end of the original concrete hearth. There is 3/4" from the top of the hearth down to the floor boards. The boards will be covered in micore, but that doesn't help with the low r value of the concrete.

Any advice would be great.

 

[begreen]

Micore is soft. I'm concerned about the rigidity of 1/4 cement board and cracking if the hearth is stepped on. I would use 1/2" Durock. The hearth value needs to be K 0.84 which the 1/2" of micore will achieve. The concrete section should be ok as long as it is solid concrete down below. If really concerned you could remove the tile and then create a new continuous hearth that has micore under cement board all the way to the fireplace opening. In that case an extra layer of cement board may be needed on the floorboard side to raise the level to the concrete side of the hearth.