The State of Oregon Building Codes Division has recently amended their requirements for Lateral Force Bracing to coincide with those of ASCE 7-05 Section 13.5.6.2.2 item c. Lateral Force Bracing is only required for suspended acoustical ceilings that exceed 1,000 square feet. Previously the Oregon Building Codes Division required lateral bracing for suspended acoustical ceiling to be installed whenever the ceiling areas exceeded 144 square feet. With this change, NWCB was able to merge the two separate 401 documents into a single document. Along with the merger, the current 401 document has been updated to reference the most current sources such as the 2009 IBC, ASTM E 580/E 580M-08 and ASCE 7-05. We ask that you download the updated 401 Document, retain the superseded version for your files and distribute the revision to your field staff.

There is one item in the 401 document that deserves a cautionary note. In the section that addresses Hanger (Suspension Wires) is a sentence from CISCA Zones 3-4 that discusses the use of a trapeze when obstructions prevent the use of a suspension wire. “Trapeze suspensions shall be a minimum of back-to-back 1-1/4 inch cold-rolled channels for spans exceeding 48 inches.” There are limits to the capability of back to back channels so we should be prudent with their use. It is not unusual for the placement of ductwork to require a trapeze that is six feet long, and you will rarely be asked to provide documentation that the back-toback channels in a six-foot length provide adequate support. The problem usually arises when the size of the duct is such that you need to trapeze for ten feet or greater. In situations such as this you may be asked by the inspector to provide verification/engineering that you have provided adequate support.

ASTM E 580 states it a little differently from CISCA when it says: “Trapeze suspensions shall be sized to resist the dead load and lateral forces appropriate for the seismic design category,” sounds a lot like engineering language. Large ductwork and/or other mechanical equipment may put you in a situation where a standard trapeze system is not adequate.

During the bid process, if mechanical drawings are available, take a look to see if there are MEP elements that may require engineered trapeze systems. If there is obvious MEP interference you should clarify your Bid Proposal so that all costs associated with a non-standard trapeze system are the responsibility of others.

If you have questions about the latest revision, call the NWCB office in Seattle at 206.524.4243 or in Portland at 503.295.0333. TK