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Alternate 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.

Basic Connections, Perimeter, and Lateral Splay Bracing  


  • Minimum intersection strength limits @ MT / CT

180 lbs

  • Vertical hanger wire 12-gauge @ 4' o.c.


  • Connection device from vertical wire to the structure above must sustain min 100 lbs


  • Main tee classifications


  • 1 in 6 max plumb of vertical hanger wires

Required if perimeter hanger wires are used

  • Perimeter vertical hanger wires not more than 8" from wall


  • Grid end/wall clearance

Min 3/4"

  • Perimeter closure (molding) width

Min. 7/8" with ACM7 Seismic Clip

  • Grid connection to perimeter attached on two adjacent walls


  • Perimeter tee ends tied together

Required (ACM7 Seismic Clip satisfies this requirement)

  • Horizontal restraint (splay wires or rigid bracing) within 2" of intersection and splayed 90° apart at 45° angles


  • Compression posts (struts) 12' o.c. in both directions, starting 6' from walls


  • Splay bracing connection strength 200 lbs or the design load, whichever is greater


  • 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



Light Fixture Attachment



  • Light fixture (all types) mechanically attached to grid NEC 410-16 (two per fixture unless independently supported)


- Surface-mounted fixtures attached to grid


Not required

- Pendant-hung fixtures directly supported from structure with 9-gauge wire (or approved alternative)



- Rigid lay-in or can light fixtures


≤ 10 lbs – one wire to structure (may be slack)



11 to 56 lbs – two wires from housing to structure (may be slack)



≥ 57 lbs – supported directly to structure by approved



Light Fixture Supplementary Hanger Wires



  • Intermediate Duty Main Tees with cross tee rating below 16 lbs./LF


- 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


- 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



  • Air terminals

≤ 20 lbs – positively attached to grid



21 to 56 lbs – positively attached to grid and two wires to structure (may be slack)



≥ 57 lbs – directly supported to structure



  • Sprinkler heads and other penetration clearance

Min 2" dia. opening or a swing joint

  • Cable trays and electrical conduit independently supported and braced




  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.