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.
Fireplace attic chase.
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.
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.
Inspecting the firebox clearances is more challenging.
Doing this leaves room to encircle the chimney pipe.
The interior of the chase has plenty of clearance to the fp and chimney.
The rsf manual in the section about chases though they mean outer wall chases says.
We also recommend to insulate the ceiling of the chase just as if it were in the attic space.
Seldom do we think about the fireplace metal vent pipe running up through the attic and roof.
Fire stops are self describing.
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.
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.
The base of the chase must accommodate the framing dimensions of your fireplace.
You can also taper the chase above the fireplace.
The chimney chase top chimney chase cover is usually metal constructed of formed aluminum or stainless steel.
Climb into your attic and locate where your chimney system will enter this space.
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.
My builder is saying that there is no requirement for a firestop since the chase and pipes are on the outside of the house with no floor or attic floor penetration.
If this height exceeds 15 you are okay to install a attic insulation shield.
Measure the height of the furthest point of the installation.
However a home inspector may tell you that there is no fire stop or that it is installed wrong.
The manufacturors recommendation is 1 from the fp and 2 from the chimney to combustable materials.