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Standard Seismic Applications Guide - IBC Category D, E, F

The following are all the IBC Category D,E,F2 Code Requirements for lay-in acoustical panels and direct-hung acoustical tiles.

The specifications below are for standard applications.
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Basic Connections, Perimeter, and Lateral Splay Bracing Requirements
Minimum intersection strength limits @ MT / CT 180 lbs
Vertical hanger wire 12-gauge @ 4' o.c. Required
Connection device from vertical wire to the structure above must sustain min 100 lbs Required
Main tee classifications Heavy-duty
1 in 6 max plumb of vertical hanger wires Required
Perimeter vertical hanger wires not more than 8" from wall Required
Grid end/wall clearance Min 3/4"
Perimeter closure (molding) width Min 2 "
Grid connection to perimeter attached on two adjacent walls Required
Perimeter tee ends tied together Required
Horizontal restraint (splay wires or rigid bracing) within 2" of intersection and splayed 90° apart at 45° angles Required
Compression posts (struts) 12' o.c. in both directions, starting 6' from walls Required
Splay bracing connection strength 200 lbs or the design load, whichever is greater Required
Partition attachment Bracing independent of ceiling splay bracing
Seismic separation joint4 Required for areas > 2,500 sq. ft. (or full height partition)
Rigid bracing for ceiling plane elevation changes 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
Light Fixture Supplementary Hanger Wires Requirements
Intermediate Duty Main Tees with cross tee rating below 16 lbs./LF Required
     - Min. 12-gauge hanger wires must be attached to the grid members within 3 inches of each corner of each light fixture.  
Heavy Duty Main Tees with cross tee rating below 16 lbs./LF Required
     - Min. 12-gauge hanger wires must be attached to the supporting cross tee within 3 inches of the corner of each light fixture.  
Supplementary hanger wires for Heavy Duty Main Tees with cross tee rating equal to 16 lbs./LF Not Required
Service Application 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 2" dia. opening or a swing joint
Cable trays and electrical conduit independently supported and braced Required


  1. Refers to CISCA installation recommendations for zones 3-4 via ASCE 7.
  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. Required for ceilings larger than 1,000 square feet.
  4. Where substantiating design calculations are not provided.