Standard Seismic Applications Guide - IBC Category C
Standard IBC
Category C
Standard IBC
Category D,E,F
Alternate IBC
Category C
Alternate IBC
Category D,E,F
The following are all the IBC Category C2 Code Requirements for lay-in acoustical panels and direct-hung acoustical tiles.

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Basic Connections, Perimeter, and Lateral Splay Bracing Requirements
Minimum intersection strength limits @ MT / CT3 60 lbs
Vertical hanger wire 12-gauge @ 4' o.c. Required
Connection device from vertical wire to the structure above must sustain min 100 lbs Not required
Main tee classifications Intermediate- or heavy-duty
1 in 6 max plumb of vertical hanger wires4 Required
Perimeter vertical hanger wires not more than 8" from wall Not required unless molding < 7/8"
Grid end/wall clearance Min 3/8"
Perimeter closure (molding) width Min 7/8" (or use perimeter wires)
Grid connection to perimeter attached on two adjacent walls Not permitted
Perimeter tee ends tied together Required
Horizontal restraint (splay wires or rigid bracing) within 2" of intersection and splayed 90 apart at 45 angles Not required
Compression posts (struts) 12' o.c. in both directions, starting 6' from walls Not required
Splay bracing connection strength 200 lbs or the design load, whichever is greater Not required
Partition attachment Allowed only if ceiling is able to move laterally
Seismic separation joint Not required
Rigid bracing for ceiling plane elevation changes Not required
Light Fixture Attachment Requirements
Light fixture (all types) mechanically attached to grid NEC 410-16 (two per fixture unless independently supported) Required
Surface-mounted fixtures attached to grid Not required
Pendant-hung fixtures directly supported from structure with 9-gauge wire (or approved alternative) Required
Rigid lay-in or can light fixtures
≤ 10 lbs one wire to structure (may be slack) Required
11 to 56 lbs two wires from housing to structure (may be slack) Required
≥ 57 lbs supported directly to structure by approved Required
Service Applications Requirements
Air terminals
≤ 20 lbs positively attached to grid Required
21 to 56 lbs positively attached to grid and two wires to structure (may be slack) Required
≥ 57 lbs directly supported to structure Required
Sprinkler heads and other penetration clearance Min 3/8" on all sides
Cable trays and electrical conduit independently supported and braced Not required


1. Refers to CISCA installation recommendations for zones 0-2 via ASCE 7. Max ceiling weight: 2.5 psf.

2. The above information is correct to the best of our knowledge at the date of issuance. Because codes continue to evolve, check with a local official prior to designing and installing a ceiling system. This is only intended as a quick reference.

3. All USG DONN® brand ceiling suspension systems meet these requirements.

4. Per ASTM C635.