Chimney box open to the attic... Is this normal?
My home was built in 1982, which apparently was before building codes were active in our area. After buying the home in the spring, I took an adventure up into the attic to replace a bathroom fan. I noticed that the chimney box, which is just a wooden 'box' going up the exterior of the house that surrounds the metal fireplace flue, is open in the attic. There's a cardboard barrier to keep the blown-in insulation from falling down to the fireplace. I didn't walk up to it, but it appears that I could just climb down the chimney box to stand on the fireplace itself.
The fireplace face is flush with the exterior wall in the living room. Outdoors, there is a small metal box on the backside of the fireplace area to allow airflow into the fireplace or chimney.
It looks to me that having the chimney open to the attic space can cause two problems. A) Heat build-up in the attic, which is a bad thing in the winter, and B) A fire in the chimney box would literally have an open door to the attic.
Is the chimney design correct, or should it be firewalled from the attic?