As medicine moves out of the inpatient setting and into the outpatient setting, everything from minor surgical procedures to ambulatory care will need to be supported in a medical office building (MOB). The mechanical, electrical, and plumbing (MEP) challenge of this new model is to design MOBs with enough flexibility to anticipate future growth and change, right from day one.

There are two building methods employed to ensure future flexibility in today’s MOBs: the full core, shell, and interiors build-out and the infrastructure-ready facility. Each has its own advantages and challenges, and can support a wide variety of tenants.

The build-out
In a full core, shell, and interiors build-out, the entire MOB—including spaces planned for future use—is completed up front. From drywall to the full MEP infrastructure, the entire building is move-in ready from the start.

The advantage is that the extra space is already available and ready to use when needed. Additionally, with construction costs likely to rise over time, completing the entire facility during the initial construction will likely cost less per square foot, making the build-out more economical in the long run.

At the same time, completing the building up front also requires more capital, and planning the layout, MEP equipment, and space requirements can be somewhat speculative. This often results in a maximum-capacity build-out for the space, which means that a portion or all of the MEP equipment may be somewhat oversized in anticipation of a worst-case future demand.

However, a balance can be struck.

For example, the Kovach Eye Institute in Elmhurst, Ill., chose a full core, shell, and interiors build-out for a new two-floor MOB. While the practice required only the first-floor space at move-in, the second floor was built out, complete with MEP infrastructure provisions to support a surgical center (a higher level of HVAC infrastructure and equipment, etc.) in the hopes that the practice will one day grow to fill it.

In the meantime, though, the second floor would be rented to another medical entity, so creating flexibility for the new tenant was important. Ceilings were left open, exam rooms were loosely configured, and wide-open areas were created so that any number of wall configurations was possible, per the tenant’s needs.

Additionally, tenant metering for gas and electric use was installed, while the second floor’s separate HVAC system was designed with its own controls to provide tenant independence in the event that the two entities have different hours of operation, indoor air quality (IAQ) demands, and heating/cooling requirements.  

While the infrastructure-ready MOB doesn’t include a facility completed with space for future expansion, it’s typically designed with modularity that allows for easy growth. With a lower first cost than the full core, shell, and interiors build-out, the infrastructure-ready MOB can expand at its own pace, deferring costs associated with additional equipment and space until it’s actually needed.

The greatest advantage of the infrastructure-ready MOB is that it’s first-cost friendly. If the facility never expands, then it hasn’t paid in advance to build out thousands of square feet of unneeded space. This gives the owner an opportunity to gauge its reception in the local marketplace before investing unnecessary capital costs.

The challenge of the infrastructure-ready MOB, though, is to ensure that the building’s utility feeds and core infrastructure are built for the eventual load. Additionally, because all the MEP equipment is modular to meet growth demands, there’s no central system to be expanded. Instead, new, individual equipment must be bought and installed, as needed.

This means that the day-to-day business operations of the MOB could be interrupted during expansion, as major construction will be required.

Two immediate care clinics in North Carolina each began with a 6,000-square-foot floor plan, with available growth of up to 12,000 square feet to be built out over two future phases. Working with Drive Architecture (Chapel Hill, N.C.), McGuire Engineers (Chicago) performed life cycle and energy payback analysis to determine the type of HVAC systems that would provide efficiency while allowing for ease of expansion.

As a result, modular, standardized rooftop equipment was selected, and gas and electrical service brought to the site was sized larger to anticipate the demand of the final build-out to reduce future construction challenges and additional costs during expansion.

Green matters
As more and more MOBs look to make their facilities green, there are a number of sustainable strategies that lend themselves specifically to specification in a modular setting looking to expand.

Air handling systems equipped with demand control ventilation capabilities will bring in only the amount of outside air needed to maintain recommended carbon dioxide (CO2) concentration, which helps minimize energy use and cost expenditures, while maintaining proper IAQ levels and acceptable building pressurization.

This is especially true for spaces that have varying occupancy levels. Employed with demand control ventilation, heat recovery can then extract energy from air that’s already being exhausted and repurpose it to help heat or cool the building. This is ideal for MOB spaces that already bring in a large amount of air on a constant basis, such as an operating room.

Lighting, CO2, and occupancy sensors should be employed to conserve energy and operational expenses in spaces the MOB isn’t using on a constant basis, but the right sensor needs to be employed for each application. For example, variable occupancy sensors are ideal over motion sensors for patient rooms, because they won’t turn lights off when occupied just because the occupants haven’t moved in a while. Also, sensors will need to be replaced every 5-10 years to prevent malfunction during use.

Lessons learned
Today’s MOB is a far cry from those built a quarter of a century ago. As building technology has advanced, so, too, has the MEP designer’s ability to deliver integrated systems, fine-tune controls, and promote energy efficiency in these spaces.

Some lessons that have emerged include the importance of bringing an MEP engineer onto a project during the design phase of infrastructure-ready projects, in particular. Fitting modular equipment into a predefined space once design is finalized or construction begins can limit the type of equipment that can be used and ultimately drive up the equipment and or construction price.

Prior to finalization of the architectural component of the design, there should be an intermediate phase where MEP equipment is sized, designed, and laid out to minimize surprises down the road.

Flexible zoning becomes critical in MOB design, as well, because the IAQ and load requirements of a waiting room will differ greatly from an exam room or surgical suite, so specifying variable air volume (VAV) boxes on the mechanical system will help maintain enough flexibility to allow rezoning as needed over the life of the MOB. A VAV system can be modular and, therefore, easily expandable.

Once space needs have been defined, it’s critical to choose the right HVAC equipment, not only to ensure flexibility and potential growth, but also the desired control over the indoor environment and the most cost-effective, energy-efficient solution. Smaller, packaged rooftop HVAC units (as opposed to larger equipment), for example, are ideal for growing MOBs, as they are easy to service, very available, and expandable. 

Electrical and plumbing infrastructure and utility feeds (water, power, and gas) must be right-sized for the eventual load, in order to minimize disruption and expense upon future expansion. Depending on the project, it may be advantageous to provide plumbing, gas, and electrical connection points (“stubs”) to further ease the disruption of future expansions.

Whether employing a full build-out or infrastructure-ready design, right-sized infrastructure will support equipment use throughout the MOB.

Supporting new models of care
Both the full core, shell, and interiors build-out and the infrastructure-ready building methods provide advantages and disadvantages to meet the needs of any MOB’s plan for future growth. As MOBs deliver more and more medical care, flexibility, energy efficiency, and a positive patient experience will be critical to their success. Designing the right MEP systems to support them will make all the difference.

William Ammons, PE, LEED AP, is senior mechanical engineer at McGuire Engineers Inc. (Chicago). He can be reached at William Stangeland is president of McGuire Engineers Inc. He can be reached at


For more on MOBs, see “MOBs: From The Ground Up."