I'm sending up the Bob Signal! Bob Harper, that is. Or anyone else who can tell me about these strange fireplace forms/supports.
Normally I see the boards or plywood that have been left in place from the fireplace construction, and my understanding is that they should be removed so that sparks migrating down through cracks won't fire them up.
But these are between the fireplace and the joists, which I've never seen before. They are loose when poked with the old WDO screwdriver, too.
What to do?

Attached Images

FP boards.jpg (35.5 KB, 44 views)

In an obvious move to put this post back on the New Posts list, ...

did I mention that the hearth is pretty much flush with the floor?

Well John, you have a very thin floating hearth. The forms are combustible and should be removed. Not just sparks but heat conduction hazard. The slab should be pinned into the foundation with rebar then a high psi glass fiber reinforced slab that tapers from 4-6" cantilevered from the foundation. Then they can set their finished hearth extension on that and remove the forms.

Sometimes the framing moves so much they resort to stuffing shims in the space in an attempt to support it a little. Many of these floating hearths are so weak, I expext to see someone fall down into the basement ala' Agent Maxwell Smart in the phone booth scene.

HTH,
Bob

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disgusted with some people on this forum. Out of here!

Thanks, Bob. You da man.

Hey Bob.........I personally liked agent 99, lol