what underlayment for hearth extension?

[mstoelton]

I'm installing a Clydesdale in my livingroom. The elavated hearth is 20 inches deep. I will need to create a new hearth pad on the floor below the existing hearth to extend the hearth and allow for the 3-6 inches of hearth that will be covered by the clydesdale. I'm planning to extend the hearth using marble tile, but I need some underlayment with the proper R value to get me to the minimun R value as specified in the hearthstone specs.

What should I use as underlayment for the tile?

 

[BobUrban]

welcome from another Michigander - please provide more info regarding the R value requirements and photos of the hearth if possible. More info than you will need provided by many here after that.

 

[mstoelton]

The necessary r value is 1.0. The hearth/fireplace is elevated ~10 inches above carpeted floor. Current hearth top is 8 feet long and 20" deep marble. Will post a picture as soon as I can.

 

[begreen]

Three thicknesses of Durock NextGen cement board will get you to R=1.17. Or a 1/2" layer of Micore of Fiberfrax under that marble will also suffice.

 

[KindredSpiritzz]

can you use 3 inch thick cement blocks for a hearth pad? If so what would the R value be?

 

[cableman]

(broken link removed to http://www.chimneysweeponline.com/horvalue.htm)

Maybe .095 per inch if there just solid cement. Just making sure but this is not a slab and there is a wood structure under this room now?

 

[KindredSpiritzz]

actually i think its a slab, i havent tore the floor apart to fully investigate yet but in one corner it seemed i got down to concrete. That'd be good cause then i could just sit it on the poured concrete right? Just figure the 3 inch blocks would give me a nice looking raised platform.

 

[cableman]

Ya then you dont worry about r value cause there is no cumbustable under it.

I would prolly just throw some tile flat with the ground in front of the hearth, unless you dont mind building it up and you can spare the extra room it will take up.