Why are continuous headers connecting portal frames over multiple openings not recommended?


Some have interpreted the International Residential Code (IRC) to require continuous headers across multiple spans in order for the building to comply with the IRC wall bracing requirements. This application is mostly seen when there are multiple garage door openings. Some might assume that a continuous header will make the entire front wall of the garage stronger, or believe that Figures 602.10.6.2 through 602.10.6.4 require that the headers be continuous across multiple openings, extending from portal frame to portal frame. However, a continuous header is subject to buckling at intermediate walls or columns unless the walls or columns are laterally braced to prevent the wall and header from buckling. Therefore, in the case of multiple garage door openings, two or more single span headers connected to a portal frame on one end and full height studs at the other (at the intermediate wall or column) is recommended. IRC Figures 602.10.6.2 through 602.10.6.4 are confusing and can be easily misunderstood. The intent is that, for a single portal frame condition, the single span header is connected to the portal frame at one end and supported by an intermediate wall with full-height studs at the other end. For a double portal frame condition, the single span header is connected to a portal frame at each end. The figures are not detailed for a continuous header across multiple openings. In fact, continuous headers over multiple openings should not be permitted unless designed in accordance with accepted engineering practice.