/ Field knowledge · IMC 501.3.2
Insect cloth is not a ¼-inch screen.
IMC 501.3.2: exhaust terminations get corrosion-resistant screens, louvers, or grilles with openings not less than ¼ in and not more than ½ in. Hurricane-prone regions: AMCA 550 for the exact model and size. Insect cloth that drops the opening below ¼ in is a fail.
Educational 2024 IMC 501.3.2. Confirm adopted edition. Distinct from 401.5 intake mesh (residential vs other occupancy). Exhaust here is ¼–½ in for the termination, not the occupancy split. Distinct from 501.3 location. Packet: 501.3.2 PDF · ES.
- Outdoor terminations must use corrosion-resistant screens, louvers, or grilles. Openings ≥ ¼ in and ≤ ½ in. Protect against local weather.
- AMCA 550 is a hurricane wind-driven-rain test. IMC 501.3.2 requires AMCA 550 louvers in IBC-defined hurricane-prone regions.
- When the opening is in an exterior wall that requires protection/rating, also meet IBC exterior-wall opening protectives — coordinate with the architect.
Verify actual slot/mesh, not brochure nominal. Keep screens cleanable. Ask the vendor for (1) AMCA 550 letter for the exact model/size and (2) AMCA 500-L free-area vs face velocity — put both on M-601. Daily Code Talk’s field tip: keep face velocity reasonable (often 500–700 fpm) to limit water carry-over, and state your basis. That range is a field check, not a sealed selection.
Decorative grille, no ¼-in screen
Wrong opening size, no AMCA 550 in Miami-Dade, missing IBC protectives on a rated wall. Insect mesh that starves airflow. Backdraft damper in the spec and not on the termination detail.
Source: DCT 501.3.2 · intake: 401.5 · discharge: 501.3.
What to send
The louver cut sheet (opening size and AMCA marks) and whether the wall is rated.
If the exhaust louver has no AMCA 550
Send the cut sheet. MasterBuild will say whether 501.3.2 even has a 550 path — or the mesh is already outside ¼–½ in.
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. Recirculation and mesh sizes below are 2024 IMC education from Daily Code Talk — not a system selection. This page is not legal advice.