You can also taper the chase above the fireplace.
Fireplace attic chase.
We also recommend to insulate the ceiling of the chase just as if it were in the attic space.
Inspecting the firebox clearances is more challenging.
The manufacturors recommendation is 1 from the fp and 2 from the chimney to combustable materials.
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.
The chimney chase top chimney chase cover is usually metal constructed of formed aluminum or stainless steel.
Seldom do we think about the fireplace metal vent pipe running up through the attic and roof.
If this height exceeds 15 you are okay to install a attic insulation shield.
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.
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.
Climb into your attic and locate where your chimney system will enter this space.
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 rsf manual in the section about chases though they mean outer wall chases says.
However a home inspector may tell you that there is no fire stop or that it is installed wrong.
After you know where the penetration point will be for both attic and roof add 2 to all sides.
Measure the height of the furthest point of the installation.
The base of the chase must accommodate the framing dimensions of your fireplace.
Fire stops are self describing.
Smaller dimensions for a rough frame of a chimney chase are about two square feet.
They are installed to stop a fire in the chase area where the vent pipe runs through to get to the roof.
The interior of the chase has plenty of clearance to the fp and chimney.
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.