What the Code Says: Truss Placement Diagrams


What the Code Says: Truss Placement Diagrams

SBCA’s Research Report clarifies the sometimes
misunderstood role of these documents

Truss placement diagrams (TPDs) may be one of the more misunderstood documents in our industry. The belief persists that TPDs contain engineering analysis rather than serving simply as a guide to installers during the erection of trusses. This mistaken belief sometimes leads to disagreements on whether truss design engineers are required to seal TPDs and, as a consequence, assume greater responsibility than they should under what the industry and their contracts state is their limited scope of work. Fortunately, the building code clarifies the role of TPDs.

In response to this issue, SBCA has published Research Report 1511-07 for the IRC and Research Report 1507-10 for the IBC. This document can be used by component manufacturers (CMs) when speaking with building designers, building officials and others who request the CM’s TPDs be sealed.

Research Report 1511-07 explains that the majority of residential structures in the United States are built using the prescriptive standards of the International Residential Code (IRC). Trusses are engineered structural elements, considered replacements for the joist and rafter applications outlined in the code.

The 2012 and 2015 versions of the IRC specifically state (in sections R502.11.4 and R802.10.1) what information needs to be on a truss design diagram (TDD) and outline the responsibility of a truss designer to prepare it (sections R502.11.1 and R802.10.2).

To find specific language on TPDs, we have to turn to section 2303.4.2 of the 2009, 2012 and 2015 versions of the International Building Code (IBC). An exception that required TPDs to be sealed when prepared by an engineer was removed as of 2009. The intent was to clarify that a TPD is not an engineering document and therefore does not require an engineer’s seal. The rationale for the change is that a truss placement diagram is an erection diagram that either replicates or identifies the assumptions made by the truss manufacturer with respect to the information on the approved construction documents. Because it requires no engineering input, a seal from a registered design professional (such as a truss design engineer) is not required.

Jurisdictional laws come into play when we look at section R106.1 of the 2012 and 2015 versions of the IRC. This section states that the plans and specifications for a project shall be prepared by a licensed architect or engineer where required by the laws of the jurisdiction in which the project is being constructed. Many states exempt residential structures from needing licensed design professionals to prepare such documents. Under these circumstances, unless otherwise required by contract, the truss design drawings and the TPDs are often not sealed by a design professional.  

We can also turn to ANSI/TPI 1-2014 (TPI 1) for further clarification, which is a referenced standard in both the IBC and IRC. TPI 1 states that, in preparing the construction documents, the building designer is responsible for providing the truss design engineer with the information necessary to properly design the trusses for the building.

TPI 1 section states: “When the Truss Placement Diagram serves only as a guide for Truss installation, it does not require the seal of the Truss Designer (i.e. truss design engineer).” This is reiterated in TPI 1 section, which states that the truss manufacturer will prepare a TPD if required by the construction documents or contract. In this case, the TPD will identify the assumed locations of each individual truss as it corresponds to the TDD. The TPD serves only as a guide for installation and requires no engineering input, so it doesn’t require a seal. This then is true even in cases where legal requirements mandate a registered design professional design the building.

In summary, the language in the IRC, the IBC and TPI 1 is quite clear: TPDs do not require the truss designer’s seal when they serve only as a guide for truss installation.

About the Author: A graduate of UW-Madison with a degree in Journalism, Matt Tanger has five years of experience in residential home construction. As a technical writer and member of the SBC Magazine team since 2014, he works closely with members of NFC and SBCA.