Joists protruding into constructional hearth

[LMCol]

Hi all, new here.
As part of my renovation I've uncovered the original fireplace opening in my 30's semi. I intend to reinstate a proper hearth, tile and get a HETAS engineer to take it from there and install a wood burner.

The concrete constructional hearth that was in place (below a 70's outset gas fire) is/was very cracked and crumbly. The hearth is supported on a brick perimeter which also supports the joists that run perpendicular. As you can see there's currently a fair bit of stick-out and I'm unsure what the current way forward... Do I:

A - Leave as-is, build a form around the opening and pour some fresh concrete. As far as I can tell, I'd then need to make sure I choose a stove which is compatible with a 12mm non-combustable depth

B - Trim the joists flush with the inside of the brick perimeter to minimise the combustible content

C - pull up the surrounding floorboards and build additional brick support piers for the joists, shim and then trim them so they are fully outside of the hearth.

One pic is the current state of the hearth, the other is right after the infill was removed but before the flooring was taken up

Thanks in advance

 

[Deluks]

B.

Most stoves these days say something like 'hearth minimum depth of 20mm' or something.
Unlikely you'll need a stove with over 5kw output.

 

[cdbe]

I found the hearth regs a bit confusing. I would trim and support the joists off some blockwork, shutter it up and cast a 100mm (ish - depending on decorative hearth thickness) constructional concrete hearth finishing at your chosen height.

According to my MI's it's 125mm constructional including a 12mm decorative (stove dependent) (but try to find anything 12mm thick as tiles are either 8/10mm or 20mm). I did 100mm slab plus 30mm limestone.

If you're going to deviate in any way from the regs or MI's I'd run it past the installer first.

Take plenty of pictures!

 

[blup]

Rebuild the constructional hearth, and create a separate dwarf wall to take the joists, blocks on a strip of dpm will work