Actual brick fireplaces should NEVER be supported on wooden floor joists,
they should be supported by a masonry foundation on heavy footings. The
hearth may be supported by wood, and normally this is only until the
concrete sets, but this may be the hearth framing that you are seeing. If
you have problems discerning what is supported by what, it is time to call
in an engineer or somebody who knows.

"CompleteNewb" wrote in message
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We have a vaulted ceiling living room, with a fireplace at one end.
Currently the fireplace just has a stone border going around it, with the
chimney that goes to the ceiling just standard plaster wall (like the rest
of the room). We're hoping to put flagstone or some other stone face all
around it up to the top (like at those ski lodges and cabins). We're not
sure about whether we'll use real stone or cultured, but one thing I'm
concerned about is the weight. In the basement, you can look up and see
that there's some type of additional wood between the joists, like a
second little subfloor under the first, that one of my handyman buddies
thinks is just for the brick floor of the fireplace, because of the
weight.

How can we know if the floor will support the stone of what we plan to do?
Or, what could we do to just make sure it'll support anything, and not
worry about exact specs?

Any ideas, advice, etc. are appreciated, and thanks for reading.