Design & Tools

Prescriptive or Engineered Design

Structural design with wood framing typically follows one of two fundamental design approaches:  Prescriptive or Engineered Design.

Prescriptive Design


Prescriptive design is where span tables, specific detailing requirements and similar pre-defined design options and rules are used to create a code-compliant design. To the professional familiar with the process and standards, prescriptive design approaches are relatively fast to use without performing significant job-specific calculations. The construction style following the prescriptive approaches is referred to as Conventional Construction. Prescriptive structural design standards are included within:

Engineered Design


Engineered design provides much more flexibility and is applicable to any building. With engineered design, the design team is responsible for providing a structural design meeting the code and project requirements.  The design team can use conventional construction details where they are applicable, but the design is not constrained to fit within the limitations of prescriptive design standards. The model building code for most US building projects is the 2012 IBC and earlier versions.

Two primary standards, referenced in the IBC, are the basis for most engineered designs of wood-framed buildings in the U.S.:

Lateral Design


Lateral design of buildings commonly accounts for wind and seismic loading from natural events. Lateral resistance of wood-framed buildings is frequently provided by wood structural panel sheathed walls as vertical shear walls and wood structural panel sheathed floor framing for horizontal diaphragms. The basis for determining the loading on buildings is ASCE 7. The code-referenced standard for designing lateral resistance using wood members is the Special Design Provisions for Wind and Seismic (SDPWS) from the American Wood Council.

In all cases, the design team should be aware of both the specific building code applicable and amendments to the model codes and referenced standards adopted by the authority having jurisdiction over the project.