Layers of Durock considered solid.??

If you bond the layers with thinset, it will be solid. It's not about the weight, it's about the heat. When I installed my RSF, if I didn't raise it 6 inches, I would have had to have a 4 inch solid masonry hearth or a special heat shield that consisted of layers of sheet metal and expanded steel mesh. They have since rescinded that requirement.

Sounds to me like the insurance company is quoting NFPA 211 for an unlisted stove. Your stove manufacturer's instructions take precedence over that IF the stove you're installing is a listed appliance. What's the stove? Rick

Rick is right - they are quoting generic specs - so unless you have some kind of old stove with no manual or listing plate this does not apply. Use the info from the manual.....but, in most cases (anyway) 2" of Durarock will do the job - and even more so with a sheet of metal slipped somewhere in there!

OK, then that is what applies. Luckily for you, that also is the 4 sheets of Durarock, which is approx R=1.0 - so you will be veru fine as described.

Be sure that your floor is stout. I recall each 3x5 sheet of durock weighing 96 lbs. So 4 layers will require say 5 sheets at 500lbs. I whole sack of thinset and tiles at say 100 lbs. The stove at another 400+lbs, throw in a load of firewood and a man warming his bum and you're well over 1200 lbs there.

I added a pair of beams and 4 columns under my hearth to be sure. It wasn't hard and I feel better about the situation. I don't feel good about the steel studs in my elevated hearth pad, they seem too flexy so next time around I would use something solid.