Best practices for mixed-use buildings

Taking on a mixed-use structure—such as one that includes retail and residential portions—can be an engineering challenge. With all the different engineered systems involved, it can be like working on and integrating several different projects at once. A group of engineers share their experiences and offer practical advice on mixed-use projects.

By Consulting-Specifying Engineer September 29, 2014


  • Anil Ahuja, PE, RCDD, LEED BD+C, CxA, President, CCJM Engineers Ltd. Chicago
  • Jason R. Gerke, PE, CxA, LEED AP BD+C, Mechanical and Plumbing Team Leader, GRAEF, Milwaukee
  • Keith Lane, PE, RCDD, NTS, RTPM, LC, LEED AP BD+C, President/CEO, Lane Coburn & Associates, Bothell, Wash. 
  • Brian A. McLaughlin, PE, Associate, Arup, Los Angeles

CSE: Please describe a recent mixed-use project you’ve worked on—share details about the project, including building location, size, etc.

Keith Lane: Lane Coburn & Associates is working for Joy Okazaki of Keep Calm on the Ivar’s Restaurant remodel project. The project includes the remodel of the kitchen, the historic Curiosity Shop, restaurant, retail, office, and ship docking stations as well as a parking garage. When it comes to mixed use, this project has it all. Throw in the historic nature of the site and you have a complex project. Ivar’s Restaurant and the Old Curiosity Shop are famous historic destinations in the Seattle area, and we are proud to be on the design team.
CSE: How have the characteristics of such projects changed in recent years, and what should engineers expect to see in the next 2 to 3 years?
Jason R. Gerke: Design engineers should be aware of the increasing complexities that will occur as more and more various types of occupancies are combined into the same buildings. Engineers have experienced restaurants and retail under residential units for many years, but what is next? Light manufacturing occurring under or adjacent to residential? Can you live and work in the same building that is producing a manufactured high-tech project? These are ideas that should be considered: How do the possibly hazardous exhaust, loud noises, or vibrations get isolated from living or office areas in multistory buildings?
CSE: Please explain some of the general differences between retrofitting an existing building and working on new construction.
Keith Lane: In my opinion, retrofitting an existing building is always more complex than designing a new building. First, you must ensure that you have proper as-built information that includes all renovations since the original build. This can be very difficult. Then you must ensure that the new retrofit meets the owner’s new power density requirements and all applicable codes. In some projects, this requires a completely new service, but a comprehensive analysis needs to be complete prior to making this recommendation. Additionally, the telecommunication system typically requires a major overhaul. These retrofits have to be done in a cost-effective manner to ensure the project is viable.

Anil Ahuja: Retrofitting existing buildings is always a unique challenge due to lack of existing condition information and especially when occupancy changes. Over the years codes have changed, ventilation requirements have changed, lighting level requirements have changed, etc. The existing infrastructure, be it electrical service, existing ventilation systems, domestic water service, heating plants, etc., is not always capable of handling new or anticipated demand. The existing structure can also create obstacles that you would not normally see in new construction. In existing structures and retrofit projects, the existing building limitations and conditions must be accommodated as it is far more difficult to change or modify.
Gerke: New construction is always the most talked about, glamorous design everyone wants to do. The only problem is that almost everyone can do it. Engineers are able to design energy-efficient and well controlled systems that work with a new building. They can ask the architect and structural engineer to push and pull the building size to fit the systems. Engineers designing for retrofitting existing buildings have the challenges of working with what is already in place for structure and space. Sometimes it is more work to achieve energy-efficient and cost-effective design within the constraints of an existing space. 
CSE: What are some challenges you have faced in coordinating structural systems with mechanical, electrical, plumbing, or fire protection systems?
Ahuja: On a recent school project in the city of Chicago, a new annex was being added on to the existing building. The existing building was partially below grade. Because the addition required the addition of an elevator to connect the new and existing buildings, it created a unique structural condition that required a great deal of coordination in order to fit all mechanical and lighting above the finished ceiling while maintaining adequate ceiling heights throughout the building. The ductwork was flattened as much as possible, and the light fixtures were changed to a low-profile type fixture to reduce the amount of depth required above ceiling. Plumbing was rerouted in structural web with openings in beams for small pipes. The structural element was driven by the existing building and elevator requirements, which in turn created a great deal of coordination among all trades to facilitate a functional system.
Gerke: One of the biggest challenges we face is the limited floor-to-floor heights and access shafts that ascend through the building. Many older buildings where we are designing for retrofits of existing spaces have heavy construction types, and knocking a hole here or there can be a big deal. Other challenges related to building structural systems include adding equipment on existing roofs not designed for any equipment loads, much less capable of meeting today’s code requirements for wind or snow loading.
CSE: Describe any recent mixed-use development project (residential, commercial, retail, cultural, or a mixture of building types) you worked on. What were its challenges and benefits? 
Ahuja: We are converting a single-owner project in Chicago’s West Loop area to a multi-tenant and mixed-use project due to a change in business of the original owner. A few things we are doing to convert the building and attract tenants is adding amenities like a fitness center, hoteling within office spaces, a restaurant and bar, a small retail space, and artwork in the lobby; opening a patio for an outdoor experience; and using a roof garden to attract networking events. This creates challenges of retrofitting the existing engineering infrastructure and accommodating existing infrastructure not designed for mixed-use.
CSE: When dealing with space constraints (tight floor-to-floor conditions), what tips or tricks can you offer to other engineers? What type of clash detection systems or software do you use to help avoid problems? 
Gerke: We model everything in Autodesk Revit, working closely with structural engineers and project architects to ensure the details that we need for coordination are included in the BIM designs. Our office considers system types requiring minimal overhead space. Hydronic based heating/cooling systems help reduce ceiling space, and dedicated outdoor air systems (DOAS) also reduce distribution ductwork sizes. Another tool in our toolbox is Autodesk NavisWorks. This program is very powerful and can be leveraged in various ways to identify clashes, coordinate spaces, or provide 3-D views to assist in visualization of what a building will look like after construction.
Lane: You can use all the complex CAD and conflict resolution systems and programs you want, but simple communication between the design teams is the most critical to avoid problems in construction.
Ahuja: The best method of dealing with tight space constraints is communication and coordination. Space constraints are an issue on almost every project because space used for systems, while critical, is unusable space to the occupant. The larger that space is, the less money-generating space the client has, and therefore the smallest space possible is what is provided. There are many software programs to use for collision detection, but the best method to avoid collisions is still communication, coordination, and research.
CSE: Because mixed-use buildings must often be flexible (tenants change, space use changes), what are some best practices? 
Brian A. McLaughlin: It is crucial to set expectations for the project early on and among all stakeholders. The design team will generally incorporate flexibility that is reasonably accommodated within the context of their design; however, that amount of flexibility needs to be agreed upon. Additional flexibility in modulating the size of leasable space or having an ability to use a space for a variety of occupancy types is generally easy to facilitate early in the design process. It is important for the design team to communicate with the owner on the cost impacts of flexibility to ensure that the owner’s expectations are consistent with their understanding of the project cost.
Ahuja: Best practices are treating each space with the understanding that it will change in the future. For instance, if you have a large, open office that requires a large amount of ventilation, provide multiple variable air volume (VAV) boxes in the space instead of a single, large VAV box that serves a large bulk area. If the client decides to renovate or separate small sections in the future, you have the boxes available for modifications. Electrically, always have meter boxes with spaces for future meters and ensure core building load is always on a separate meter.
Gerke: Never design the system to have the minimum capacity required on day one. While the systems cannot be oversized per the current International Energy Conservation Code (IECC), systems should have the capability or at least the ability to be modified for additional capacity in the future. Another extremely important practice is to size vertical and horizontal building shafts for future systems. These spaces are very difficult to carve out later when surrounding spaces are occupied by tenants.
Lane: It is always best to discuss the initial and potential long-term use with the owner and design team during design. During the design process, provide options for the electrical distribution with pros and cons. Work with contractors to provide pricing for these options. Then with the design options, pros and cons, and pricing, the owner can decide on the best route to take based on upfront costs as well as long-term suitability of the systems.