Structural engineers share tips on assessing structural systems when purchasing an existing building for adaptive reuse.
Purchasing or leasing an existing building for adaptive reuse is a major investment for any company looking to expand business opportunities. Making the right decision can provide long-term benefits for a company’s success—paying off in thriving growth, new market gains, and new recruits.
Typically, companies turn to brokers to identify a building for purchase or lease, building inspectors to review systems, and architects to design or renovate space. Yet one other building professional should be part of the pre-purchase planning decision. Structural engineers offer insight into the future viability of a building for adaptive reuse—and they can identify hidden hotspots efficiently.
Depending on how a building owner intends to reuse a space, a building’s structural integrity can impact successful renovation. By reviewing existing building drawings and renovation plans during a pre-construction walk-through, structural engineers can evaluate a building’s viability on several key points.
Change in Occupancy
Buildings are designed for specific programming loads and other requirements based on their intended use. A change of occupancy can change these requirements. Is the building up to the challenge?
For instance, medical buildings often include specialized equipment with specific load or vibration requirements. Reinforcing the floor structure for the addition of heavy imaging equipment can be relatively straightforward. A more difficult challenge occurs when this equipment, or similarly sensitive equipment like laboratory microscopes, have specific vibration requirements. Designing floors for vibration is complex and is not done unless the requirements are known during the initial period of construction. Reinforcing floors to improve vibration performance is even more difficult. The risk associated with placing sensitive equipment on poorly performing floors is reduced accuracy, and poor return on investment for the potential owner.
Similarly, medical office buildings often include rehab facilities with treadmills, free weights, and other equipment that induces noise and vibration. Heavy sound-absorbing mats can be used to reduce some noise and vibration, but beyond that it can be difficult and expensive to improve performance for a floor that is susceptible to vibration issues. A structural engineer can inform the potential owner if the floor is robust or prone to long-term noise and vibration issues.
The load capacity of the roof structure is particularly important when considering mechanical system placement. For instance, medical clinics often require more roof-top HVAC equipment than other building types, such as office buildings. Additionally, imaging equipment and light booms often have components that are hung from the underside of the existing roof. A review of the existing drawings can provide insight on the roof’s ability to support additional loads. Buildings with composite steel-concrete roofs tend to have additional capacity and can often accommodate new equipment and openings with little reinforcement. Buildings constructed using bar joists and metal roof deck are often designed for the exact loads expected and thus have zero excess capacity. It could also be anything in between, and a structural engineer can advise the potential owner on the necessary reinforcement.
Punching through floors for stairway or elevators also need special structural consideration.
Architects and engineers working together can determine the best location to cut through a floor. An opening that makes the most sense from a programming perspective may not be the most cost-effective from a structural perspective, potentially requiring additional reinforcement to support the floor. Finding a suitable compromise can minimize structural cost and still meet the tenants needs.
Elevator openings need similar consideration. The type of structure may dictate the type of elevator used. For example, elevators that require machines located at the top through a pulley system may impose large loading that the building’s floors (or roof) were not designed to support. In that case, a different elevator may be required, in which the machines are mounted within the assembly and loads only the floor of the elevator.
Structural bearing and non-bearing walls may appear identical—but removing a bearing wall can compromise the structure. It is important to identify bearing walls and how to reinforce them when considering new punched windows, egresses, or even removal to create open floor plans. Bearing walls typically serve as part of the building’s lateral system acting as shear walls. In these cases, modifications need to be investigated for both gravity and lateral loading.
Upgrades to existing foundations may prove cost prohibitive because of the effort to excavate soil and temporarily support the structure from within the building. Increasing occupancy load, adding heavy rooftop equipment, or vertically expanding the building may require foundation upgrades. An overloaded footing may settle into the soil, causing floors to slope, walls to crack, or damage to equipment.
Another potential cause for a foundations upgrade is building age and code changes. If the snow load or lateral system requirements have changed because of code updates, and if the planned renovation increases the stress in any member by more than five percent, then the foundation systems needs to be brought to up to current code. The changes may impact the entire structure, but the foundation upgrade may be the costliest.
A final foundation consideration is elevator changes. Elevator upgrades may require modification of the existing elevator pit depth. If the elevator is in the proximity of existing foundations, a lower pit may not be practical.
When engaged early in the leasing and planning process, structural engineers provide cost-effective, proactive expertise that benefits adaptive reuse. Buildings originally designed for flexibility can offer limitless reuse possibilities, while others will require expensive modifications to serve a different purpose. The best strategy for a potential building owner is to begin the planning process early by working with an experienced engineer to achieve optimal results.
About the Authors
Ben Shock, PE, is a Senior Structural Project Engineer at HGA.
Anton Tillmann, PE, is a Structural Engineer at HGA.