We also recommend to insulate the ceiling of the chase just as if it were in the attic space.
Fireplace attic chase.
The manufacturors recommendation is 1 from the fp and 2 from the chimney to combustable materials.
As currently designed the distance inside the chase to the chimney or firebox will be more like 24 on average with the closest spot about 6.
Any wood that is too close to the chimney will undergo a process called pyrolysis and even catch fire at temperatures as low as 200 degrees.
They are installed to stop a fire in the chase area where the vent pipe runs through to get to the roof.
The chimney chase top chimney chase cover is usually metal constructed of formed aluminum or stainless steel.
If this height exceeds 15 you are okay to install a attic insulation shield.
Seldom do we think about the fireplace metal vent pipe running up through the attic and roof.
We find leaks here especially where the top is framed and enclosed flat and the top flashing lacks adequate pitch and stiffness to avoid collapsing even becoming concave where there are snow loads.
Most of the units inspected by chimney professionals are improperly installed and a trip to the attic to check clearances is definitely time well spent.
A chimney installer indicated that i would need a firestop in this chase between the first second floor and another one 8 feet up from that.
Fire stops are self describing.
The base of the chase must accommodate the framing dimensions of your fireplace.
If the climate in your area is very cold insulate the chase to the top to keep the chimney warmer increase the draft and reduce creosote buildup.
Smaller dimensions for a rough frame of a chimney chase are about two square feet.
The rsf manual in the section about chases though they mean outer wall chases says.
Inspecting the firebox clearances is more challenging.
You can also taper the chase above the fireplace.
The interior of the chase has plenty of clearance to the fp and chimney.
Doing this leaves room to encircle the chimney pipe.
However a home inspector may tell you that there is no fire stop or that it is installed wrong.
Measure the height of the furthest point of the installation.