Plain English:
505.4 makeup air required: If a domestic kitchen hood system can exhaust more than 400 cfm, you must provide makeup air at approximately the same rate.
Makeup air must have a means of closure (damper)
It must automatically start and run whenever the hood exhaust runs (interlocked control)
505.5 common multistory domestic kitchen exhaust: If multiple dwelling kitchen hoods connect to a shared vertical riser/shaft, the "common system" has strict rules:
The duct must be in an IBC-rated shaft.
Dampers are prohibited in the exhaust duct (except where 505.3 allows). Shaft/duct penetrations must be protected per IMC 607.5.5 Exception 2.
Use rigid steel duct inside the shaft: min 26-gauge and built per SMACNA.
No offsets in the shaft ductwork (keep it straight).
Fan/motor safety: motor per IMC 503.2 and located outside the airstream.
Fan runs continuously and must be on standby power.
Fan status must be monitored and alarm/indication provided if it's not operating.
If any individual kitchen exceeds 400 cfm, it still needs makeup air per 505.4.
Provide a cleanout at the base of the shaft: min 12 in x 12 in.
No screens at the termination.
The shaft serves only kitchen exhaust and must be independent of other exhaust.
On Plans: Why it matters
The 400 cfm trigger is where "simple residential hood" becomes a pressure/control problem. And once you go to a common riser, it's no longer "duct routing" - it's a life-safety shaft system with standby power, monitoring, cleanouts, and strict construction rules.
Code Path: Where to show it
M-001: "IMC 505.4 MAKEUP AIR" note: HOODS >400 CFM REQUIRE MUA APPROX. EQUAL TO EXHAUST, WITH AUTOMATIC START/STOP INTERLOCK AND MEANS OF CLOSURE.
M-101: Identify any kitchens on a common riser and label "COMMON DOMESTIC KITCHEN EXHAUST RISER PER IMC 505.5 (RATED SHAFT, NO OFFSETS)."
M-601: Riser/fan schedule fields for CONTINUOUS OPERATION, STANDBY POWER, FAN STATUS MONITORING, MOTOR OUT OF AIRSTREAM, CLEANOUT PROVIDED.
Check: Do
Check hood submittals early for "capable of >400 cfm" and coordinate makeup air before ceiling layouts lock.
If using a common riser, coordinate shaft rating, cleanout access, standby power, and monitoring with Arch + Elec from day one.
Review Risk: Don't
Don't treat a common kitchen riser like generic exhaust.
Don't provide makeup air without an automatic interlock to the hood exhaust.
Field Tip:
On multifamily jobs, add a small "HOOD >400 CFM?" checkbox next to each kitchen tag. If YES, add "MUA INTERLOCKED" right on the plan. It prevents the classic late surprise where the hood cut sheet triggers 505.4 after ceilings are already coordinated.
Masterbuild QA Lens
Domestic kitchen exhaust airflow rates are not code-specified in the IMC for all scenarios - ASHRAE 62.2 or the residential code may govern. Confirm which standard applies for the project occupancy, whether the listed fan provides the required cfm at the actual duct system static pressure, and that the rated airflow is achievable with the installed duct length and elbows.
Drawing / Submittal Check
For makeup air and multistory kitchen exhaust (505.4-505.5): the drawings must show the makeup air source, the air balance for the space, and the control sequence linking makeup air to the exhaust fan. For multistory common exhaust, show the riser diagram with each unit's connection, the fan capacity, and the fan serving each unit.
Common Review Risk
Makeup air for large residential range hoods (over 400 CFM) is frequently not addressed in the design. When the hood is specified at 600 or 800 CFM, the building pressurization drops significantly - combustion appliances backdraft, doors are hard to close, and infiltration brings in unconditioned exterior air. Size the makeup air to match the exhaust rate and show the source location on the drawings.
When To Escalate
Escalate when makeup air for a large residential kitchen range hood is not available from the exterior without significant penetration of the building envelope, and for multistory common kitchen exhaust riser systems where the fan serving upper units does not have sufficient capacity due to stack effect or long duct runs.
Rated Assembly Coordination
Makeup air and common multi-appliance cooking exhaust ducts that cross rated assemblies require appropriate dampers. Confirm that each combination of appliances sharing a common exhaust trunk has a compliant penetration detail at every rated wall and floor crossing.
Kitchen Exhaust Coordination
For kitchen exhaust, tie the hood schedule, appliance lineup, grease duct route, cleanouts, fan discharge, fire suppression interface, and make-up air strategy into one reviewable story.