To brace ducts.


Provide transverse and longitudinal bracing in accordance with theSMACNA Seismic Restraint Manual Guidelines for Mechanical Systems.

Supplies Required

  • Steel angles—size varies with ducts
  • Machine bolts—1/2″ diameter
  • Sheet metal screws—No. 10


  1. Provide angle braces sized in accordance with the SMACNA guidelines. Attach together with machine bolts. Maximum spacing is 40′ for transverse bracing and 80′ for longitudinal bracing.
  2. Provide screws at 18″ on center maximum from the bracing to the duct.
  3. Attach bracing to the structure above in accordance with the SMACNA guidelines.


  • Bracing is required at ducts exceeding 6 square feet in cross-sectional areas, and for round ducts exceeding 28″ in diameter.
  • No bracing is required if the top of the duct is 12″ or less from the support above. See SMACNA guidelinesfor hanger requirements.
  • Walls, through which ducts pass, can be substituted for transverse braces. Provide blocking around the duct.

Duct Bracing
Source: Noson, Perbix, SSD