Repair/Reinforce Hearth Joists

[EmberEnergy]

I'd like to repair some termite damage that's unfortunately located in/around the hearth framing and floor joists.

I am looking for any intel to determine how my hearth was built. My hope is it is a monolithic slab with rebar tying it into the chimney and foundation wall but what are ways to confirm that is the case? Also, to check my understanding, if the hearth is a monolithic pour and is tied to chimney by rebar, the floor joists and framing surrounding the hearth are not actually bearing the load of the hearth once concrete has cured, correct?

I've attached a diagram and pics. In terms of damage, the small ~4ft joist and small inner framing wood (highlighted red) are completely toast and the larger ~14ft sister span (highlighted orange) has moderate damage that gets worse toward the right side of the house if facing the foundation wall. I think the double short joists framing the sides of the hearth are essentially undamaged, or superficial damage. All joists are 16" on center. None of the main floors sag or bounce and the hearth is not cracking away from the firebox - there isn't any structural damage I can see aside from termite damage to the joists.

If the hearth isn't depending on the floor joists, I would think the repair becomes much easier and I could put jacks up in the spots I have denoted with green circles just to be safe. For repairs, I am thinking to replace the ~4ft joist entirely. For the sistered run, I would take the outer one off and if the inner one looks ok, I'd just replace the outer one. If I need to replace the inner sister, that would be trickier cause I'm assuming I might need to re-secure to the slab - really long tapcons and washers?

 

[kennyp2339]

You can always just build some temp supports using 2x4 studs in the vertical position, cutout the bad pieces and when installing the new joists double them up and using joist hangers to tie them in.

 

[EmberEnergy]

You can always just build some temp supports using 2x4 studs in the vertical position, cutout the bad pieces and when installing the new joists double them up and using joist hangers to tie them in.

Yeah the challenge will be the dang central air handler sits directly under the middle of the sistered run so looking for a creative way to provide adequate support.

Do you mean joist hangers for the very ends? The brick wall has a 3-4" ledge and then provisions (holes) in the block wall for each joist including both sisters so the new joist would sit in the same recessed hole. Or were you thinking something else for the hangers?