Sizing the facility: How did this place get so Big?
One of the more difficult and confusing tasks during the predesign phase of a new hospital project is sizing the facility appropriately. Hopefully, by the time functional and space programming (allocating space room-by-room and department-by-department) begins, there is a consensus as to the scope of the project. Generally, the core functions of the hospital will be known, such as the number of emergency room spaces, the number of ORs, the scope of the lab, and the number and allocation of beds. Typically shown as a ratio of square feet to beds, rules of thumb and standards are available to determine the square footage that should be built, based on the number of beds.
Relying solely on these ratios prior to the completion of a detailed design is not, however, recommended. It is crucial to go through the process of functional and space programming in order to get the building from net to gross square feet, and to ensure your facility is appropriately sized prior to beginning the design process. Understanding this conversion, and the terms pertaining to this process, will also help to explain why the building turns out to be larger than originally thought.
Healthcare providers are well-versed in acronyms such as NPO, QID, ICU, APR-DRG and, of course, ROI. Hospital executives know the meaning of these acronyms and use them daily. Architects and healthcare facility planners have their own acronyms used for space planning: NSF, DGSF, FGSF, and BGSF. Understanding the meanings of these acronyms is the key to understanding predesign facility sizing.
NSF: Net square feet. NSF refers to the inside, wall-to-wall dimensions of each individual room or the amount of floor space a particular space may involve. For instance, an operating room may be shown in terms of 625 NSF, a scrub station at 10 NSF, or an office at 100 NSF. These spaces include only the amount of bare physical space inside a room before finishes are applied. Wall thickness (internal walls between rooms) is not included. Once a space program is developed, the individual rooms in each department are added together for a sum total NSF for that department/area.
One important note: NSF differs from clear square feet, which may be referenced in design guidelines or standards and codes (AIA guidelines, state building codes, etc.). Clear square footage refers to the amount of square footage available in a room/element once in-room components are taken into account (e.g., fixed cabinetry, toilet fixtures, door swings). Space programming should be done using NSF, not clear square footage standards.
DGSF: Departmental gross square feet. This term is defined as the total of room-by-room dimensions plus internal departmental factors such as internal corridors and partition wall thickness. Once a department's individual room elements are added together, the resulting NSF is multiplied by a departmental grossing factor (DGF) to calculate DGSF. For instance, the DGF includes estimated allocation of intradepartmental spaces, departmental wall thickness, and intradepartmental corridors. DGSF is sometimes referred to as useable square footage or the departmental footprint. Departmental grossing factors are expressed in decimal form (e.g., 1.40 means an additional 40% of space to the NSF, to account for departmental gross). Grossing factors vary by function/department and generally range from 1.20 to 1.60. For example, an inpatient unit with 8-foot-wide corridors and wall thicknesses that include medical gasses will typically have a grossing factor of 1.50 to 1.60, while an administrative area with 5-foot-wide corridors and standard drywall thickness may have a grossing factor of 1.20 to 1.30. Using an appropriate departmental grossing factor during programming and predesign will ensure that the designed square footage closely matches the programmed square footage for each department.
FGSF: Floor gross square feet. This is defined as the total of DGSF plus interdepartmental factors such as corridors between departments. It is the inside scope of each floor footprint—the sum total of all DGSF on a particular floor plus those areas not typically associated with, or dedicated to, a particular department/function. These include elevators, internal internal stairwells, main interdepartmental corridors, minor computer rooms, minor mechanical rooms, and exterior walls. The floor grossing factor averages from 1.20 to 1.35 (an additional 20-35%), depending on the scope of the floor plate envisioned. The more discrete functions located on a floor, the larger the factor. This takes into account circulation from department to department, as opposed to a floor with one function, such as a medical/surgical nursing unit, where most circulation space is accounted for in DGSF. Under-sizing floor gross by failing to account for the above elements will result in a final design larger than originally forecasted in the program.
BGSF: Building gross square feet. This is defined as the total building envelope, that is, the total of FGSF plus a building infrastructure. The last piece of the puzzle is getting from FGSF to BGSF. The building gross factor (BGF) applied to the sum total of all FGSF takes into account perimeter stairs, major mechanical spaces, penthouses, and a central energy plant. A building gross factor in the range of 1.08 to 1.12 is typical. Some planners and programmers may jump directly from DGSF to BGSF. In that case, they must ensure that a factor of 1.35 to 1.45 is used to get from departmental to building gross.
Design factors impacting building size
Unique features such as curved walls, extra-wide concourses and corridors, atriums, courtyards, architectural icons, and monumental staircases are just a few elements that will push BGSF even higher. This is not necessarily a bad thing, but it is advantageous to be aware of this during the design phase and the capital project budgeting process.
In summary, until the building is fully designed it will not be known just how large the BGSF truly is. Simply totaling up the NSF will not determine the total size of the building. Knowing NSF is just the beginning. Typically a grossing factor is applied to the NSF in order to get the total size of the building. The NSF is multiplied by a factor to get to DGSF. After all DGSF are totaled, they are then multiplied by a factor to get to FGSF and so on, until total BGSF is known. Once all grossing factors have been applied, the BGSF of a new building is close to twice the size indicated by the NSF, and appropriately so. If there are no unique architectural features and the net-to-gross conversion factors resulting from design are exceptionally large, the efficiency of design should be questioned.
Predesign sizing and budgeting can minimize surprises during the design phase if the factors involved in programming are understood and appropriately applied. HD
Curtis Skolnick, MHA, is a a Principal Consultant with KLMK Group, LLC, based in Richmond, VirginiaRichmond, Virginia.
Healthcare Design 2009 February;9(2):38-41