Truss Bracing At Supports
Question:
I almost always see wood trusses erected with no stability bracing at points of support. It seems to me that common sense and section 3.3.3.4 of The American Wood Council’s National Design Specification for Wood Construction (NDS) require that lateral support be provided at points of bearing. Plywood decking doesn't provide any more restraint for a wood truss than it does for a roof joist. I doubt if it was a concern with short span trusses having 4 in. high heels, but I see lots of longer span trusses with energy heels that are not braced. At times, it is hard to draw the line between an energy truss and a bottom chord bearing truss. When a truss can clearly be identified as bottom chord bearing, there is not as much resistance to bracing it. When I tell someone that the trusses should be braced, I cannot point to a code requirement that specifically addresses this facet of bracing. Is there any published guidance on a requirement for this type of bracing?
Answer:
The type of permanent bracing that you are describing is part of the building design that needs to be calculated by the building designer, who should then provide details about required bracing. This is bracing which is ultimately part of the diaphragm design.
There are requirements for lateral restraint in IRC 2012/2015 R802.8, IRC 2012/2015 R802.10.3, and IRC 2012/2015
R602.10.8, which includes requirements specific to braced wall lines and especially related to seismic concerns. This section also includes specific blocking details. For additional guidance on bracing and blocking, see the following:
Ventilation v. Eaves Blocking in Seismic Zones
Connections for Tall Heel Trusses
Blocking for Trusses at Braced Wall Panel Locations
Connecting Wood Trusses to Braced Wall Panels