Plain English:
501.4 pressure equalization: Size exhaust to remove the chapter-required airflow and run it whenever exhaust is required. For spaces other than Group R-3 and dwelling units in Group R-2, keep the space neutral or negative.
If supply > exhaust, provide a relief path (natural or mechanical) for the excess.
If exhaust >= supply (or exhaust-only), provide makeup air to cover the deficit.
501.5 ducts: When this section doesn't specify construction, follow Chapter 6 for duct materials, gauges, joints, supports, fire/smoke provisions, and terminations.
On Plans: Why it matters
Missed makeup air or no relief path = door whistling, odor migration, poor capture, pressure alarms, and comfort complaints.
Code Path: Where to show it
M-001: Note pressure intent (neutral/negative where required), makeup-air/relief rules, and "duct construction per Chapter 6 unless noted."
M-101/102...: Arrow the airflow balance by room; show makeup-air and relief routes; tag pressure sign (N, NEG, or BAL).
M-501 details: Air device placement/installation, transfer/relief grilles, backdraft dampers; typical duct joint/seal note referencing Ch. 6.
M-601 schedules: Room/Zone | Required Exhaust (cfm) | Supply (cfm) | Target Pressure (NEG/NEU) | Makeup-Air Source (OA/transfer/dedicated MAU) | Relief Method (RA/relief fan/transfer) | Duct Construction Note (Ch. 6 ref).
Check: Do
Balance on paper: list supply, exhaust, pressure target, and the exact path for makeup/relief.
Place makeup air so it supports capture (e.g., feed the room, not the hood face).
Review Risk: Don't
Rely on door undercuts alone for large offsets.
Leave exhaust-only rooms without a defined makeup-air path.
Assume "per code" covers duct gauges, joints, or supports-cite Chapter 6.
Field Tip:
Add a small "PRESSURE & MAKEUP-AIR" schedule on M-601. If the sum of exhaust exceeds supply for a zone, highlight the deficit and show the makeup-air device and path feeding that zone.
Masterbuild QA Lens
Pressure equalization (501.4) is most commonly missed on exhaust-only rooms - bathrooms, janitor closets, telecom rooms. Confirm each exhaust-only space has a documented makeup air path: door undercut, transfer grille, or mechanical OA supply. If the exhaust exceeds supply by more than a small margin, the space goes negative and contaminant migration follows. Show the pressure intent on M-101.
Drawing / Submittal Check
The permit set must address pressure equalization for any building with mechanical exhaust that could create negative pressure - show makeup air source location, makeup air rate, and the control sequence linking exhaust to makeup air. Duct construction table must be referenced on the drawings: confirm duct gauge and SMACNA class match the static pressure in the duct schedule.
Common Review Risk
Pressure equalization failure - exhausting more than the makeup air provides - is common in energy-conscious projects where makeup air is minimized to reduce heating and cooling loads. If the building goes negative, doors are hard to open, exterior air infiltrates through uncontrolled paths, and combustion appliances may backdraft. The energy model and the mechanical air balance must be reconciled before the permit set is issued.
When To Escalate
Escalate when the pressure equalization analysis shows the building will go significantly negative under any realistic operating scenario. A building that operates at negative pressure has air quality and combustion safety problems that cannot be solved by adjusting the exhaust rate alone. Escalate to a full building pressurization analysis before the permit set is finalized.
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.
Duct System Coordination
Pressure-equalization and local exhaust requirements influence duct sizing, dedicated exhaust trunk routing, and how makeup air is balanced against exhaust capacity. Show both exhaust and makeup paths on the same drawing.