Pairing performance-based design with IPD for the best value
Learn about integrated project delivery and performance-based design trends, approaches, and challenges.
Learn the requirements of delegated design.
Review design-assist and design-build project case studies.
Integrated project delivery (IPD) is an ongoing development of the design and construction industry. This is a trend that promises to become more prevalent each year. The collaborative focus of IPD forces the engineer to reassess their approach to a project, determine how to best allocate the development of the overall design to capitalize on the skills of the contractor, and maximize the efficiency of project delivery.
One way to do this is to use a performance-based design methodology in the development of the project documentation. In other words, identify the desired outcome while leaving the exact methodology of execution open for interpretation and innovation by the contractor. This seems like a simple undertaking; however, it can be difficult for an engineer to allocate aspects of design responsibility to the contractor while maintaining “direct supervision and control” over the design as required by most professional regulations for the engineer of record (EOR). Alternatively, a delegated design approach could be used, as described below.
Delegated design approach
Delegated design is a fairly common approach for specialty-scope portions of projects, such as a curtain wall for a high-rise building or systems that are very prescriptively defined by codes and standards, such as fire sprinklers. For example, for sprinkler systems, the scope definition provided in the bid documents can be limited to identifying the incoming water source and the required design density for sprinkler application, with the balance of the system design left to the installing contractor, who becomes the EOR for the system. This approach has its shortcomings, most notably in coordinating space requirements for equipment and location of visible components during the design phase, such as control valves, hose outlets, and the sprinklers themselves. The lack of defining these needs early in the project’s design can lead to challenges for the project team when allocating space for fire pump rooms, establishing power for pumps and alarm devices, and coordinating the sprinkler layout with other ceiling elements. Additionally, owners are typically interested in the quality of materials used and the system’s ability to be reconfigured in the future.
Including more definition in the scope documentation, such as providing material specifications, showing and scheduling fire pumps, routing fire and sprinkler mains, locating standpipe risers and zone-control valves, and coordinating sprinkler locations, can resolve many of these issues. This more detailed approach provides more control over the overall design; however, unless the documentation is developed to the point of providing pipe routing down to the branch-pipe level and hydraulic calculations to demonstrate the functionality of the design, the approach is still considered a delegated design by most municipalities.
By contrast, other systems—such as HVAC, plumbing, and electrical—are much more prescriptively described in the bid documentation. Consequently, in most cases, the design engineer is still responsible for the design as EOR. In the traditional design-bid-build approach, these systems are identified from incoming utilities, through source equipment down to terminal elements, including distribution between each element. Incorporating BIM technology has, to some level, exacerbated this prescriptive model. Design engineers are using this technology to model and coordinate systems distribution prior to bidding, with the thought that the contractors can then fine-tune this design to facilitate installation.
While modeling detailed systems has allowed design engineers to be more efficient by having the ability to automate component schedules and calculations, the time spent coordinating the distribution during the design phase to the level that is needed to allow this automation is significant. The value of that effort is never truly recognized unless the model can be transferred to the contractor and used in the development of materials take-off and fabrication, which often is difficult to execute due to software differences between the engineer and contractor. Additionally, unless the design engineer has significant input from the contractor, this approach can limit the ability to incorporate elements that are easier to make and install, such as prefabricating components. Prefabrication can provide significant benefits via reduced installation time and improved product quality.
Bridging the gap by using the IPD approach
The IPD process seeks to bridge this gap by bringing the design engineer and contractor together in a collaborative team that brings the talents and insights of all participants together to optimize project results, increase value to the owner, reduce waste, and maximize efficiency through all phases of design, fabrication, and construction. By using an IPD approach, the design engineer develops the system parameters to a level that defines major components, main systems distribution, controls, and operational strategies to meet the required or anticipated performance. Based on the abilities of the contractor, various aspects of the design completion are then left up to the contractors to complete rather than the engineers. This often includes the detailed coordination and final distribution to terminal devices, typically based on criteria established by the design engineer, but it can also include final equipment selection based on performance requirements, the layout of mechanical rooms, or other aspects that benefit from considering the installation sequences and logistics.
This allows the contractor to determine common approaches to repetitive elements, increasing the ability for components to be prefabricated and the installation to be expedited. The contractor may also provide input on components and control strategies based on the equipment’s cost or lead time, ease of installation, or other characteristics that make the construction faster and more efficient. This approach has been characterized as design-assist in the past to differentiate it from design-build, in which the engineer provides a preliminary design that is completed by the contractor, who is the EOR.
In the design-assist IPD approach, the portions of the system that were developed by the contractor are defined by pre-established criteria. The design engineer maintains control over the system performance and design parameters, oversees the completion of the design by the contractor, and is still considered the EOR.
Design-build projects use an approach where the engineer is contracted to develop an initial design intent to a schematic level, and the completion of the design is then procured through a competitive process from one of several contractors. In this situation, the schematic-level design produced by the engineer is similarly performed to define spatial requirements for equipment rooms and distribution pathways, initial system selections are made, and the performance requirements and space conditions are defined. The competitive procurement process then allows the various bidding contractors the flexibility to suggest alternative approaches that are beneficial from a cost standpoint. Once the project is awarded, the contractor becomes the EOR and is responsible for completing the design and creating and stamping the permit drawings. The design engineer is sometimes retained to review and comment throughout the project and provide assurance that alterations still meet the initial design intent. This approach requires that the contractor have one or more licensed engineers on staff to act as the design professional who is responsible.
Can the design-assist or design-build IPD approach be considered performance-based design? By definition, performance-based design is a design whereby a building is required to meet certain measurable or predictable performance requirements, such as energy efficiency or seismic load, without a specific prescribed method by which to attain those requirements. It would seem that both can, to a greater or lesser degree. The contractor’s limitations to completing the design based on system selection and criteria established by the design engineer in design-assist would make this approach less performance-based. Involving the engineer early in the design to facilitate selecting and coordinating systems with building elements is included in both scenarios.
When the contractor is brought into the process, the design engineer will typically already have determined the type of system that will be used and the size and location of major components. The design-assist approach incorporates the contractor’s input, but the performance of the overall design is still the responsibility of the engineer. The design-build approach crosses over to delegated design, and the contractor in this scenario has the ability to not only influence selections and facilitate coordination, but also make measurable improvements in project results by altering the systems altogether. Including the contractor in system selection and equipment placement can provide insights on durability, ease of maintenance, and procurement and installation timelines. Leaving system selection up to the contractor gives them the responsibility of the system’s performance and the overall design. Like previously mentioned in the approach to sprinkler system design, in the design-build approach, the design engineer develops certain performance parameters and metrics to exert control over the design decisions, but then only provides assurance that the final design meets those parameters. The contractor becomes the party responsible for these decisions, so the EOR role would be delegated to the contractor.
The ability to scale back the level of documentation developed by the engineer to allow the contractor to have more freedom and flexibility in selecting systems is limited not just by the assignment of design responsibility, but also by the design process. The building design process requires the interaction of multiple parties from the very outset to determine project requirements, support elements, adjacencies and configuration of spaces, pathways for communication, as well as system distribution. For a building design to advance, it is necessary to define the potential systems to a level that allows the location of equipment spaces and clearances to access all parts of the facility.
Collaborating for project success
In a collaborative approach between the architect and engineer, the decisions related to selecting and coordinating systems are based on the needs of the building, placing equal importance on system performance and lifecycle cost as they do on available space. Considering the location for equipment spaces is weighed against the performance of various system types, their ability to serve the needs of the building, and their long-term efficiency. The ultimate building design that emerges can be greatly influenced by the systems that are selected and how the equipment is placed, such as when an interstitial floor is used for equipment and distribution. Having the engineer work collaboratively with the architect at the very start of a project allows this approach to flourish and for true system integration into the building’s design, rather than relegating systems and equipment to the spaces that are leftover once the building has been configured.
At the most basic level, selecting systems to deliver the required performance involves a choice between types and numbers of components and configurations that can provide the same result at perhaps a different initial cost, operational efficiency, maintenance frequency, and anticipated lifespan. That selection can be made on a variety of characteristics: budgetary allowances, reliability, space constraints, availability, and owner prerogative.
Once the initial building layout has been established in the early design stages, the choices become more limited. Even still, this is an area where the design engineer and the contractor can partner on performance-based design. If the contractor is brought on board at the point where the engineer is still considering a variety of system solutions at different layouts, price points, and efficiencies, the contractor can then assist in determining the most advantageous solution while meeting the desired result. The initial effort to coordinate space requirements might allow the building to be configured at this time, but there are still many decisions to make to take advantage of the collaborative process.
The choices can be between significantly different design approaches, involve the quantity and size of components, or include options related to enhanced performance or future flexibility—provided that they all generally can fit within the allocated space. By identifying the general equipment type and operational strategy of various options, the design engineer can set the stage for a thoughtful interaction with the contractor to facilitate a decision driven by input from both parties.
The two case studies illustrate the variation in levels of collaboration incorporated into an IPD process. The first describes a process where the initial system design was developed by the design engineer and the final distribution coordination was completed by the contractor based on parameters developed by the engineer. The second describes a process where the initial design effort was used to define system performance requirements established from a preliminary design, after which the engineer, contractor, and owner collaborated on the review of various reconfigurations with the requirement that the preliminary design’s performance was maintained or improved. While the collaboration is useful in both cases, only the latter can be considered performance-based design.
Daniel Fagan and Robert Ward are lead mechanical engineers and office engineering leaders at their respective offices for CannonDesign. Each has more than 30 years of experience in the construction industry and has worked on numerous projects including commercial, institutional, health care, and education facilities. Management of more than $100 million worth of construction annually has provided them with knowledge of a variety of project approaches and delivery strategies.