Hidden fireplace

Kathy asks: 

We recently bought a bank owned property and found that a previous owner had covered an original wood burning fireplace. The drywall was screwed to a 1x2 which was jammed into the front of the firebox. The firebox seems to be intact, but the hearth and all surrounding brick are gone. Originally (from looking at neighbors') it would have had a brick hearth and surround topped with a wooden mantle. There is a ceramic tile floor that goes to the fireplace wall, and drywall all around the opening. 

Do I need to rebuild a hearth, or can I simply tile around the firebox opening and add a mantle (per local safety codes) to save the floor space?

Jake's answer:

Kathy,

That was quite a find.

You should have the firebox inspected by a licensed chimney inspector prior to using the firebox.  For the purpose of our discussion, I will assume it is a traditional wood burning fireplace.  The 2006 International Residential Code requires a hearth slab thickness of 4”.  The hearth extension in front of the opening needs to be 16” if the fireplace opening is less than 6 square feet and 20” if the fireplace opening is greater than 6 square feet.  The hearth side extensions need to be 8” on each side if the opening is less than 6 square feet and 12” on each side if the opening is greater than 6 square feet.  Combustible materials, such as wood trim and mantels, should not be placed within 6” of the fireplace opening.  Combustible material within 12” of the fireplace opening should not project more than 1/8” for each 1” distance from such opening.