Tips to design multifamily and mixed-use buildings

Multifamily dwellings and mixed-use buildings are becoming more prevalent. Some best practices and tips are offered for engineering systems in these residential buildings.

By Consulting-Specifying Engineer July 26, 2017


  • Brian Berg, PE, LEED AP, CEM, Associate Principal, Glumac, Irvine, Calif.
  • David Crutchfield, PE, Principal, RMF Engineering, Charleston, S.C.
  • Kieran Healy, PE, Mechanical Engineer, CCJM, Chicago
  • Lui Tai, PE, Technical Services Director, JENSEN HUGHES, Toronto
  • Robert J. Voth, Executive Vice President, Bala Consulting Engineers, King of Prussia, Pa.

CSE: What’s the No. 1 trend you see today in the design of multifamily dwellings and mixed-use buildings?

Brian Berg: We’re seeing a lot of large complexes taking the “mixed” part of mixed-use to the extreme. Retail, restaurants, offices, hotel, residential, grocery stores, and parking are typically being built as part of one large complex. Oftentimes, this is being done on a multilevel podium with tower(s) stacked on top. And sometimes all those uses are in one tower. Parking is either all underground or a combination of underground and wrap-style lots where residential units line up around the aboveground parking. These are all being built in either dense urban areas or less dense burgeoning areas near an abundance of public transportation options.

David Crutchfield: One interesting trend we are seeing is a desire for mixed-use spaces to support lifestyle activities. For example, occupants often want an in-house gym or space for outdoor activities. We’re also seeing an increasing number of people working or studying from home, so they need flexible mixed-use spaces that can accommodate their lifestyle. Overall, this indicates a larger movement toward people becoming increasingly reliant on their homes or dorms to cater to all their needs underneath one roof.

Kieran Healy: A growing trend we have seen within the Chicago housing market is the retrofitting of central cooling systems into low- and mid-rise multifamily buildings that were built in the 1980s or earlier. To stay competitive with new construction, property managers have needed to provide cooling in buildings that were often only heated with perimeter fin tubes or in-slab radiant flooring. Many owners have opted for water-source heat pumps or variable refrigerant flow (VRF) systems to reduce the overall energy required to both heat and cool the building. These systems are unique in that a vertically tiered renovation approach can be used to keep the majority of units occupied while others are being renovated.

Lu Tai: In Ontario, the recent trend is to install automatic sprinkler protection in multifamily-dwelling units, such as retirement and care homes. After a few high-profile incidents in retirement and care homes from the last decade where there were reported fatalities, the fire code is mandating that these types of buildings be reviewed to comply with the retrofit code. Within the retrofit code, there is the mandatory requirement that all such multifamily homes be retrofitted with automatic sprinklers by the year 2019.

Robert J. Voth: Amenities remain a highly attractive part of the development as competition for occupants is intensifying in markets outside of New York City. Additionally, mixed-use developments are moving to a smaller-scale, very efficient build model.

CSE: What other trends should engineers be on the lookout regarding such projects in the near future (1 to 3 years)?

Healy: Developers are becoming increasingly competitive with each other as they strive to capture and maintain residents in mixed-used facilities. Be on the lookout for more luxury amenities, such as full fitness and yoga studios, conference centers with commercial kitchens, rooftop pools and spas, and lobby bars and coffee shops. Mechanical, electrical, and plumbing (MEP) systems have to be sized to allow that flexibility, supporting longer-duration occupancy of common areas versus a transient occupancy where residents are only passing through from interior to exterior and back.

Crutchfield: The infrastructure to support personal devices, such as cell phones, tablets, and laptops, for people who work from home have driven a need for higher levels of cabling and power in mixed-use buildings. Connectivity solutions, such as USB chargers built into receptacles and information technology (IT) wiring ready for the next level of bandwidth, are becoming standard and critical to building a marketable project.

Tai: The use of alternative solutions to resolve issues that do not match the prescriptive requirements of the building code. This is particularly true for new builds, but can also apply to existing facilities. In new construction, alternative solutions allow more flexible designs that are not envisioned by the prescriptive code; and in existing facilities, they allow less destructive work to take place.

Voth: Suburban markets centered around multi-use “villages” will remain a strong market. Engineering firms will need to understand the 4-story stick-built-over-concrete development model to remain competitive.

Berg: These complexes seem to be getting bigger and more prevalent. My office is in Southern California. The state has a housing shortage right now, so housing is popping up all over the place with multifamily mixed-use projects as the developments of choice. This is what we see locally, but we have projects throughout the state and country of similar types.

CSE: Please describe a recent project you’ve worked on—share details about the project including location, systems engineered, team involved, etc.

Tai: Recently, we took on a project to design and install automatic sprinklers into 75 existing retirement-home facilities across Canada (for one owner). Because it is a retrofit project, the level of difficulty was increased. We had to come up with innovative engineering methods to do the work that would cause only minimal impact to existing residents and deal with possible asbestos issues, disease outbreak, and inadequate water supplies. To avoid costly errors and delays, we worked with a procurement company to schedule and administer the work, completing the $55 million project within 18 months to the satisfaction of the owner.

Voth: The Bridge in Philadelphia is an efficient 17-story building with 146 apartments. The project used a VRF system and central domestic hot-water generation to obtain U.S. Green Building Council LEED certification. The team included the build partner from the beginning of the project, which led to a very efficient design and build process. Time to market was less than 20 months.

Healy: The Fannie Emanuel Senior Apartments is a 20-story senior-living facility with 181 single-bedroom apartments owned by the Chicago Housing Authority (CHA) in Chicago’s West Garfield Park neighborhood. As part of a $61 million gut-rehab project, we worked with Holabird & Root as the architect and Old Veteran Construction as construction manager to completely redevelop the 132,000-sq-ft building on a 2.5-acre site originally constructed in 1963. As the MEP/fire protection (MEP/FP) engineer for the project, we selected systems to increase comfort and accessibility for senior citizens and brought fire alarm and sprinkler systems up to current code. HVAC systems included a 276-ton air-cooled heat pump VRF system with ducted evaporators, condensing boilers with panel radiators as supplemental heat, dedicated outside-air system (DOAS) with energy recovery for corridor make-up air and toilet exhaust, and demand-controlled ventilation (DCV) system for 1st-floor offices and community spaces. Plumbing systems included new condensing-water heaters, intelligent domestic booster pump, and low-flow plumbing fixtures. Electrical upgrades included new 4,000-A switchgear and metered distribution, video surveillance and IT infrastructure, LED lighting fixtures, and a 350-kW generator for life safety and standby loads.

Crutchfield: RMF Engineering was the MEP engineer for the Coastal Carolina University Student Housing project in Conway, S.C. The complex consisted of 333,100 sq ft and 1,270 beds in a series of stand-alone buildings. This project used DOAS to provide code-required ventilation air and building make-up air. Fan coils with heating and cooling coils are provided in the rooms to allow for individual room climate control. In addition to the dorm rooms, community spaces were provided on each floor at a ratio of two large community spaces, one quiet student room, and one living room per 35 residences. Wireless and wired internet connectivity, access control and security systems, high-efficiency laundry machines, a convenience store and student cooking kitchen, custodial and maintenance storage, apartments for live-in staff, administrative offices, and reception and meeting space were all included in the buildings. Outdoor spaces incorporated sand volleyball courts, a covered pavilion complete with a fireplace, a grilling area, and plenty of courtyard green space.

Berg: We’re working on a high-rise project in downtown Sacramento, Calif., that’s wrapping up construction at the moment. The project has two levels of underground parking; four podium levels of retail, restaurants, and offices; and a 12-story tower with hotel and residential units on top of the podium. We selected a condenser-water system to serve multiple types of water-cooled HVAC equipment to suit the occupancy use. The design team is located in southern California, with the owner and contractors being local Sacramento firms.

CSE: What are the challenges that you face when designing such facilities that you don’t normally face for other building projects?

Crutchfield: Often, the budget is the biggest challenge for developer-driven projects where the return on investment has been carefully calculated for the financing, and the engineered systems must fit into the budget. With the market rebound that has occurred since the end of the Great Recession, the escalation of trade contractor costs has caused projects that were estimated and budgeted 12 months prior to be over budget by over 10%. When this happens, it is a challenge to reduce cost for the engineered MEP systems while still ensuring they function properly and are as sustainable as originally designed.

Healy: In multifamily dwellings and mixed-use buildings, horizontal and vertical space is a premium that tenants and landlords fully use. Vertical shaft space is reduced to a minimum, floor-to-floor heights are minimized, and interstitial space between ceilings and slabs are lower than other building types. When space is at a premium, it becomes extremely challenging to coordinate layering of ductwork, plumbing piping, sprinkler piping, and electrical conduit in very tight ceiling plenums. The use of BIM models and construction mock-ups can help solve these complex coordination challenges.

CSE: What are some unique elements/considerations to designing/retrofitting multifamily dwellings and mixed-use buildings?

Voth: The existing building floor plate is key, as the configuration for an efficient unit layout will drive the development opportunity. We have typically engineered all new systems in our retrofit projects; therefore, incoming services need to be reviewed carefully, especially the domestic water, sanitary, and gas services, as residential projects demand a higher usage for these services.

Berg: There are always living spaces nearby where we want to put equipment. Acoustics become a big issue in the HVAC world, but we need to be extra conscious of equipment selections, locations, and acoustic- and vibration-mitigation measures with living quarters throughout. Make sure there is always an acoustical engineer on the design team for these types of projects to help inform the MEP designs. Architects and developers often want to move the emergency generator to the roof so it is out of the public’s view and/or kept out of subterranean parking to allow for more spaces. Moving a generator out of the garage would also help lessen HVAC costs to get radiator exhaust and engine exhaust out of the building. Locating on the roof causes its own set of challenges, necessitating fuel day tanks, rated shafts for the fuel lines, and an expensive floating slab to deal with vibrations during generator exercising if it’s located on top of living spaces.

Tai: For retrofit projects of multifamily-dwelling buildings, the biggest consideration is to minimize impact to existing residents. This includes the design, which would require the least amount of work done within each dwelling unit and the most work done in common areas. Detailed to-the-hour scheduling is required on a daily basis to ensure that any work required within residents’ spaces are completed, so residents can return to their units as scheduled. In a senior-living environment, infection control is another major consideration.

CSE: Is your team using BIM in conjunction with the architects, trades, and owners to design a project? Describe an instance in which you’ve turned over the BIM model to the owner for long-term operations and maintenance.

Healy: Our experience on numerous projects has been that the design model was not shared with the construction team. Whether for design-liability reasons or otherwise, we just haven’t seen the logical extension of sharing the design model with contractors nor have we had clients requiring this in conventional design-bid-build projects. This may change in design-build projects where the designer and the builder have a contractual relationship that may offset liability concerns.

Voth: All of our projects are delivered in BIM. To date, we have not turned a BIM model over to an owner in the mixed-use market space, we have turned BIM models over in our corporate and higher education projects. We have typically taken the BIM model to LOD400 and then turned it over to the contractor for the construction period.

Crutchfield: BIM has become the normal tool in the design of all buildings. RMF has not delivered a job in CAD in about 18 months. The next step in pulling the most functionality out of BIM is getting the long-term facility staff to use the model as a tool in the operation of the facility. A cultural shift is slowly unfolding in which the facilities staff is outfitted with the devices necessary to access and use a BIM model. We suggest that each project’s closeout materials be provided on an iPad/laptop that is preloaded with the BIM model and necessary maintenance-scheduling software. We have noticed that if we don’t drive the transfer of technology this way, the facility staff will print a set of drawings as they’ve always done in the past. If there is a paper set of drawings on the site, the electronic documents may never be accessed again.

Tai: Traditionally, sprinkler designs are completed using more specialized software, such as HydraCAD and SprinkCAD. We are watching the trend in using BIM closely and have switched to AutoSprink, which is a software specially made for sprinkler design in 3-D and is compatible with other BIM drawings created in 3-D. At the end of the project, the 3-D model showing the control valves and pump controls are turned over to the owner(s) to allow them to visually prepare for the required periodic inspections.