IMC 801.3 is short - masonry chimneys must be built per the IBC - but it's one of the highest-value coordination flags in Chapter 8. A masonry chimney can't be designed on the mechanical sheet alone; it has to agree with architectural and structural construction at every point it touches the building.
Plain-English Highlights
Masonry chimney construction follows the IBC, which means location, construction type, structural support, fire-resistance, clearance to combustibles, shaft/enclosure conditions, roof penetration, flashing, liner requirements, cleanout access, and termination height all need to show up coordinated across disciplines - not just noted once on the mechanical plan.
Permit Proof Chain
Appliance requiring chimney service -> masonry chimney construction basis (IBC) -> liner type matched to appliance and fuel -> structural support and fire-resistance coordination -> roof/wall penetration and flashing -> cleanout and termination detail.
Where To Show It
M-001: chimney/vent notes and appliance venting criteria. M-101: appliance location and chimney connection. M-501: chimney connector, liner, cleanout, roof penetration, and termination details. M-601: appliance schedule with chimney/venting basis. A sheets: chimney construction, roof penetration, exterior wall coordination. LS sheets: rated walls, shafts, fireblocking, separation requirements. S sheets: chimney support, anchorage, framing coordination.
**Do** - Coordinate masonry chimney requirements with the architectural and structural sheets, not just mechanical. - Show liner type, appliance connection, cleanout, and termination together. - Confirm the chimney is actually suitable for the appliance being served. - Address existing chimney reuse with a documented condition and liner assessment.
**Do Not** - Treat a masonry chimney as a mechanical-only note. - Show "existing chimney to remain" without stating the review criteria. - Skip roof, shaft, rated-assembly, or combustible-clearance coordination.
Masterbuild QA Lens
Run a side-by-side check: does the mechanical vent path match the architectural and structural chimney details? A masonry chimney that's correct on M-101 but uncoordinated on the A and S sheets will still fail review.
Drawing / Submittal Check
Confirm the architectural sheets show the chimney's construction type, fire-resistance rating, and roof penetration/flashing detail, and that the structural sheets show support and anchorage - both independent of, but consistent with, the mechanical liner and connection detail.
Common Review Risk
The recurring miss is an existing masonry chimney marked "to remain" with no liner size, no condition note, and no clearance-to-combustibles verification - especially on renovation projects where the chimney predates the current appliance.
When To Escalate
Escalate any new appliance connecting to an existing masonry chimney, any chimney passing through a fire-rated assembly or occupied shaft, and any condition where roof framing or exterior wall construction conflicts with the chimney location.
Field Tip
When reviewing a masonry chimney, put the mechanical vent path next to the architectural and structural details side by side. If construction, liner, cleanout, support, and roof penetration aren't all coordinated across those sheets, the design isn't permit-ready.