/ Field knowledge · IMC 801.19
Two floors, one vent shaft is the comment.
Appliances on different floors generally cannot share the same venting system. The exception is narrow: every appliance in a room accessed only from outdoors, and the enclosure does not communicate with occupiable areas. An exterior door is not enough if a corridor door, grille, or shaft still opens into the building.
Educational 2024 International Mechanical Code (IMC) 801.19 from Daily Code Talk. Confirm the adopted edition. Distinct from solid-fuel dedicated flues (801.11) and positive-pressure venting (801.9). Gas appliances also follow the fuel-gas code. This is not a common-vent design.
- Default: common venting systems serving appliances on more than one floor level are prohibited.
- Exception — both conditions together: all appliances served are in rooms or spaces accessed only from the outdoors, and those enclosures do not communicate with occupiable areas (no openings, doors, grilles, shafts, or other pathways into occupied space).
- A mechanical room that happens to have an exterior door still fails if a corridor door or a shared shaft communicates with occupied floors.
On the set: one line per appliance on every common vent — ID, floor, enclosure type, and whether the enclosure communicates with occupied space. If more than one floor is in the table and both exception boxes are not yes, the common vent is not acceptable as drawn.
Two mechanical rooms, one shaft
A common vent serving two floors because both rooms share a shaft, with the exception assumed rather than demonstrated, reaches both the mechanical and architectural drawings. Do not leave floor configuration to field coordination after the riser is installed.
Source: Daily Code Talk — IMC 801.19 · solid-fuel: 801.11 · mechanical draft: 804.3 · existing: 801.18.
What to send
Appliance schedule with floor levels, the common-vent / riser diagram, and architectural access into each mechanical room (exterior door, corridor door, shafts, louvers).
If two floors share a vent shaft
Send the riser and the room access. Masterbuild will say whether 801.19 even has the exception — or the common vent has to be split.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. This page is 2024 IMC 801.19 education from Daily Code Talk — not a common-vent design. This page is not legal advice.