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What Is Included in a Structural Calculation Package? A Guide for Owners and Builders

A contractor submits a permit set for a two-story addition. A few weeks later, the plan checker returns a comment: “Provide structural calculations supporting the framing shown on the structural sheets.” The drawings looked complete, yet the project stalls. This situation is common, and it usually traces back to a simple question: what is a structural calculation package, and why does a building department ask for one?

A structural calculation package is the engineer’s written record of how a structure was designed. It documents the criteria, loads, analysis, and member checks that justify every size, spacing, and connection shown on the structural drawings. The drawings tell the builder what to build. The calculations explain why it is adequate.

This article explains what a complete package contains, how it is organized, which code provisions govern it, and how owners and builders can recognize a package that will move smoothly through plan check. At JMVC Consulting Structural Engineers, we prepare these packages for projects of many scales, and the same fundamentals apply whether the building is a single-family addition or a multi-story commercial structure.

1. Design Criteria and Basis of Design

Every credible package begins with a statement of the design basis. This section tells the reviewer what rules the engineer followed and what assumptions were made before any number was calculated.

A typical basis of design identifies the project address and a brief description of the structure, the governing building code and its edition as adopted locally (for example, the International Building Code with ASCE 7 for loads), and the design method used, either Load and Resistance Factor Design (LRFD) or Allowable Stress Design (ASD). It also lists material properties, such as the lumber species and grade, the specified concrete compressive strength f’c, reinforcing steel grade, and structural steel specification.

Soil and foundation criteria

The allowable soil bearing pressure is one of the most important assumptions in the entire package. When a geotechnical report exists, its recommended value governs. When it does not, IBC Table 1806.2 provides presumptive load-bearing values that depend on soil classification, ranging from 1,500 psf for clay and silt soils to 2,000 psf for sand and silty sand, among other categories. IBC Section 1603 requires that the structural design criteria and design loads be shown on the construction documents, so the values stated in this section must match the drawings exactly.

2. Gravity Loads and Member Design

The gravity section establishes the loads that act on the structure and then checks each element that carries them, from roof framing down to the footings.

Dead loads are calculated from the actual assemblies: roofing, sheathing, framing, insulation, finishes, and mechanical equipment. Live loads come from IBC Table 1607.1; for example, 40 psf for most residential living areas, 30 psf for sleeping rooms, and a 20 psf minimum roof live load. Snow loads are determined from ASCE 7 Chapter 7 based on ground snow load, exposure, and roof geometry. These loads are combined using the load combinations in ASCE 7 Section 2.3 for LRFD or Section 2.4 for ASD.

Checking beams, joists, headers, and columns

Each member is checked for bending, shear, bearing, and deflection. For wood members, the National Design Specification for Wood Construction (NDS) governs, including adjustment factors for load duration, size, and repetitive use. For steel, AISC 360 applies; for concrete, ACI 318. Deflection is checked against the limits in IBC Table 1604.3, where floor members are commonly held to L/360 for live load. A beam can satisfy bending and shear and still fail this check, which is why a floor that is technically strong can feel bouncy.

The package should also trace the load path. A post that carries a beam must be shown to deliver its load to a footing, and the calculations should make that chain visible from the roof to the soil.

3. Lateral Analysis for Wind and Earthquake

Lateral design is where many incomplete packages fall short. Reviewers expect to see both seismic and wind forces evaluated, with the controlling case clearly identified.

For seismic design, the engineer establishes the site class, the mapped spectral accelerations, the seismic design category, and the response modification coefficient R for the selected system. The seismic base shear is then calculated using the equivalent lateral force procedure of ASCE 7 Section 12.8, where V = Cs x W, and distributed vertically to each level. For wind, ASCE 7 Chapters 26 through 31 define the basic wind speed, exposure category, and the resulting pressures on the main wind force resisting system.

From lateral force to shear walls and anchors

Once the controlling lateral force is known, it is distributed through the diaphragms to the vertical elements. In wood construction, shear walls are designed using the AWC Special Design Provisions for Wind and Seismic (SDPWS), which provides the unit shear capacities for sheathing and nailing. The package should show the shear demand on each wall line, the selected sheathing and nail schedule, the overturning moment, and the required hold down anchors. Collectors, or drag struts, that deliver diaphragm forces into the walls should be checked as well./p>

4. Foundations and Connections

The final technical section confirms that the load reaches the ground safely and that the pieces of the structure are tied together. Footing widths are sized by dividing the service load by the allowable bearing pressure, then checked for flexure and shear under ACI 318 where reinforcement is required. IBC Chapter 18 governs foundation requirements, including minimum depths and anchorage.

Connections deserve the same attention as members. Anchor bolts or anchors at the sill plate, hold down hardware, beam to post connections, and ledger attachments should each be supported by a calculation or by a manufacturer’s evaluated capacity. In practice, a surprising number of field problems originate at connections, not at the members themselves.

5. What Plan Check Reviewers Look For

A package is judged on more than its arithmetic. Reviewers want to see that the calculations and drawings describe the same building. They typically look for an index and consistent sheet references, a clear statement of assumptions, software input and output that can be followed, and a signature and seal from the responsible licensed engineer.

The most frequent cause of resubmittals is a mismatch: a beam size in the calculations that differs from the drawings, loads that do not match the criteria on the cover sheet, or a lateral system that is drawn but never analyzed. A well organized package avoids these comments by keeping every number traceable from assumption to result to detail.

Conclusion

A structural calculation package is not paperwork added at the end of a project. It is the engineering foundation behind the drawings, covering design criteria, gravity loads, lateral forces, foundations, and connections in a form that a plan reviewer can verify. Knowing what belongs in a package helps owners and builders ask the right questions and avoid costly delays during permitting.

If you are planning a project that requires structural calculations, or you have received plan check comments you would like help interpreting, you are welcome to contact JMVC Consulting Structural Engineers to discuss your needs.