Contractor-Ready Construction Documents—Part 2

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Design decisions are typically based on previous experience, engineering judgment, and code requirements. However, the project location, general contractor, trade partners, and local practices may impact the structural design and detailing. Contractor involvement during design can provide input on key decisions in the selection of structural systems, use of building materials, and more. Instead of value engineering after the project has been completed, contractor assistance can avoid costly redesign efforts and schedule delays. Part 1 of this series, which appeared in the December 2025 issue of STRUCTURE, discussed contractor input that affects the design of the structure. Part 2 discusses contractor input that affects detailing, constructability issues, and construction sequencing.

During design, mechanical engineers use preferred vendors to size mechanical units with their associated weights and dimensions. This information is used to size and locate beams to support the heavy load of the mechanical unit and frame around the required duct openings. Sometimes, these units are altered during the contractor’s bidding process and the weights and/or dimensions are changed. This results in potentially reframing and re-designing a portion of the structure to accommodate the final selected unit. This effort can have schedule, cost, and re-detailing implications.

Elevators are frequently put out to bid after construction documents are issued. The hoistway size, pit depth, overrun requirements, rail forces, etc. always vary between manufacturers. The surrounding structure, such as slab edges, beam locations, and mat foundations, are all affected. Projects with concrete shearwalls frequently rely on elevator shaft concrete walls to help provide the lateral load resisting system for the structure. A change in hoistway dimensions will alter the shearwalls. Recruiting contractor assistance in producing an early-release elevator package or at least selecting the elevator supplier during design can reduce the amount of redesign and re-detailing required after construction documents are issued.

Contractor input on how to handle different foundation types in varying subsurface conditions can simplify construction and save time in the project schedule.

Prefabricated exterior wall panels provide the benefit of assembly in a shop environment and speed of erection on site. Early selection of the prefab wall supplier by the contractor provides valuable input to the design team.

For projects with large floor heights and high wind speeds, the supplier can determine the wall stud depth that will be required, so the exterior wall profile is depicted correctly.

The slab edge and bent plate dimensions will be set by how much tolerance and air space is required by the selected prefab wall supplier. This can potentially impact column locations and beam/columns sizes. Steel members with large flange widths and fireproofing can potentially conflict with the wall panels (Fig. 1)

The prefab wall supplier can help define which portions of the building elevations may not prove to be efficient with prefab wall panels and when stick-framed stud walls are more appropriate. For instance, a short stud knee wall under a strip window may be more effective with stiffening channels in the stud walls compared with stud moment resisting connections at the wall base track.

Maximum panel heights and widths and joint locations can be reviewed with the prefab wall supplier, which will need to be incorporated into the building elevations and beam designs.

Where temporary or permanent earth retention systems will be required, contractor involvement, along with their preferred specialty foundation contractor, benefits the design team by providing feasible options for the project. Determining how close a new building with a basement can be located to an existing structure may be driven by the earth retention system that is used.

Locating openings in floor slabs is critical to ensure the integrity of the structure. Prefabricated bathroom pods often used in healthcare facilities have specific opening locations with minimal tolerance for field adjustments. Early involvement by the contractor and prefab supplier will allow sleeve locations to be identified prior to construction. Not having this information prior to construction may require retrofit or additional supporting structure to accommodate field cut openings. Coring through a two-way concrete system will be problematic if there is no flexibility with core locations. Existing slab reinforcement is often cut during coring, which reduces significantly the shear/flexural capacity of the slab.

Some cities and counties require structural calculations to be submitted for review prior to issuing a permit for construction. The review process may be done by the city itself or may be outsourced to another engineering firm. The city comments may lead to changes to portions of the design and detailing of the structure, which in turn affects shop drawing production, fabrication, and the start of construction. Additional time is typically required to allow for correspondence with the City to resolve any review comments and generate any additional calculations the City may require. Discussions with the contractor during design about the City review process can assist in the development of the project schedule and owner expectations.

Expanding existing buildings always requires field verification. A set of existing design drawings is not the same as having an accurate set of as-built drawings or field survey information. At the time of the existing building construction, field modifications, RFI (Requests For Information) responses, changes made to shop drawings, etc. are often not depicted on the existing drawings. Having a contractor on site during the design phase to investigate the existing building will save potential delays once construction begins. As-built conditions can affect the design in countless ways, such as the following:

Renovating or expanding existing structures frequently involves phasing to minimize the downtime of portions of the facility. Temporary exit paths and careful phasing is an important part of the project for the owner. Understanding the phasing plan may impact the design by requiring additional foundation walls to provide temporary egress stairs early during construction. Or, if beam or joist retrofits are required, the extent of work in a particular phase may need to be increased to capture the space needed for the fix.

Contractor involvement during design can help take the guesswork out of what may be preferred and considered most economical by the contractor in addition to identifying/confirming existing site and building conditions. The design, detailing, constructability, and sequencing can be optimized to provide a cost-effective project and minimize potential design and drawing changes after construction documents are issued. ■

About the Author

Jeremy Salmon, PE, SE, is a principal at Structural Design Group in Nashville, Tennessee. He may be reached at Jeremys@sdg-structure.com. Zak Pruitt, PE, SE, is an associate principal at Structural Design Group and may be reached at zakp@sdg-structure.com