By taking into account whole building performance, our designs can offer structures that are more sustainable, more satisfying to clients, and longer lasting. The trick is measuring performance.
We talk about building performance all the time: how a design works or doesn’t, how the building will perform in an earthquake or severe weather, how light shelves manage daylight, and whether a shading system works to provide occupant comfort. To date, however, the discussion about building performance has focused primarily on energy use. But as the notion of environmental sustainability has been extended to include social and financial sustainability (the triple bottom line), building performance concerns have broadened to include measures of program efficacy, occupant comfort, financial return, durability and other concerns.
Sustainability grew out of concern for atmospheric carbon dioxide and other greenhouse gases (GHG) and their effect on climate change. The most direct measure of a building’s GHG generation is its energy use. This has become the single operating metric for building performance.
Our view of architecture is evolving. In the Beaux Arts tradition, building designs were illustrated as fixed (usually black-and-white) objects often unrelated to context. Today’s architects see buildings as dynamic processes rather than static objects, almost as organisms. We see buildings as having useful life spans. They have daily and weekly cycles; they change and require maintenance during their long lives; they require the input of energy and produce waste products; their systems need to be controlled; they have a nervous system of sorts (even more so with so-called “smart buildings”). And they exist and operate in relation to the environment.
The danger of focusing on building energy is that we may fail to exert equal effort in designing for higher levels of performance in a building’s other systems. As you will see, there are many possible metrics for building performance. This article sets out to explore building performance by discussing the numerous components that go into assessing how a building meets the needs of its various users.
The U.S. Green Building Council set out to change industry practices in order to make green building the norm. It has succeeded quite well by promulgating LEED evaluation criteria and checklists for the sustainability of buildings, interior fit-outs, neighborhoods, and campuses. There are few clients these days unfamiliar with sustainability as it applies to buildings, and an increasing number are looking for designs that will result in some level of LEED certification. In addition to this interest, there is a growing desire to be able to measure objectively the way buildings perform and to be assured not only that the goals of sustainability will be met by proposed designs but that some tangible measurement of green performance can be reported. Clients want to be able to compare one design’s impact on global, regional, or neighborhood environments with another and to assess environmental costs over the life of a building. We want buildings that are to be both built and operated sustainably. Our concern for sustainability is evolving beyond a checklist and scoring process to a whole building performance evaluation. This calls for objective ways to measure and compare the performance of existing buildings and to evaluate proposed designs on a wide variety of scales. Such measurement would add a new level to building information modeling (BIM), currently employed as a means of virtual construction for analyzing potential problems prior to real-world construction. BIM will also support virtual building operation and provide a means to assess safety, security, program fulfillment, program efficacy, operating cost, maintenance requirements, and other operating parameters. With a method of simulating building operations, life cycle analyses can be more dynamic. They can better assess the impact of changes in building performance resulting from design, program, operations, maintenance, and other decisions.
The call for objectively measurable performance criteria stems in part from a desire by institutions, funders, regulators, and project sponsors to manage the outcome of the design process. Some characteristics cannot be easily measured, but that should not prevent us from considering those issues when we evaluate a building or design. Nor should it dissuade us from considering those characteristics’ contributions to whole building performance.
The whole life of any building’s design and construction proceeds through several stages:
• Ideation and conceptualization
• Purpose programming and description
• Design iterations
• Creation of contract documents for construction
• Construction to commissioning
• Move-in and startup
• Facility operations and maintenance
• Program change or repurposing
• Renovation and structural change
• Deconstruction, disassembly, or demolition
There are parallels in whole life performance management:
• Development of performance requirements
• Performance simulation
• Planning for asset operations and maintenance
• Evaluating performance through data collection and analysis
• Reprogramming for re-use or enhanced performance
BIM can be more than a static geometric data set about building materials and system components; it can be the basis for building performance simulation. The materials and spaces in the model can be given operating characteristics, and the information model can be given life and set to perform in simulated environments. We are familiar with mock-ups and testing such as ASTM fire tests, curtain wall infiltration testing, aesthetic materials mock-ups, and constructability mock-ups. Such realistic mock-ups are giving way to virtual models of constructability, virtual wind tunnels, digital hydrothermic cycling, digital energy modeling, room acoustics simulation, lighting simulations and life safety exit flow modeling. Performance simulation helps us design with efficiency of material, energy, and water use and to deliver healthful indoor environments.
Like the proverbial elephant described in radically different terms by six blind people, each feeling a single part, whole building performance looks unique to each person who touches it. To a retailer, a building performs well if it expresses the values of the brand; to a facility manager, if its systems and controls are transparent and easy to maintain; to an educator, if students perform well; to a developer, if the project sells or rents; to a banker, if the debt is repaid. Although we don’t want designers lost in the details, it is important to realize that we are designing the whole elephant. And as design has become manifestly the product of specialists working together, we want to assure that design is an integrative process tending toward wholeness, beauty, high performance, durability, and not the work of a committee (whose goal of designing a thoroughbred supposedly, through a series of compromises, resulted in the camel).
Some elements of building performance are readily measured using familiar scales. Others rely on less familiar scales. And some rely on intuition and judgment born of experience. Following are some elements of performance that might be measurable and that could therefore be described in a program, analyzed in a model, and measured in a complete building. We could then be more explicit in our design work and manage the process to create buildings that meet or exceed sustainability and other expectations.
Energy performance. This is the performance we are all most familiar with: the total net amount of energy from all sources consumed in building operation per square foot of useable space per year. The simple metric of BTU/sq ft/year has been collected by the U.S. Department of Energy and generalized for climate zones and programmatic factors for a variety of building types. This data provides a base against which to measure a design’s energy performance. Energy demand modeling simulates the use of energy throughout a typical year based on local weather data. Such models can be iterated to fine-tune the design to achieve higher levels of energy performance.
Program performance. There is a growing interest in facility performance evaluation that deals with how well the occupants of a space are performing. By extension, if occupants perform well on a series of metrics such as business productivity, absenteeism, educational achievement, self-reported thermal comfort, change in reported environmental-related illnesses, or in time-and-motion studies, the facility is said to be performing well. That such performance can be measured in the operation of a completed facility leads to the notion that it might be programmed a priori. Space programs giving expected area and some description of activities or user needs are usually provided as the basis for architectural design. Since a given level of performance (beyond just satisfying a numeric program) is anticipated, measures of performance might be discussed and agreed to beforehand as part of the program.
Measuring how well a design meets such a space program is straightforward. It can be as simple as a chart comparing design areas to the program area or to the useable area provided for the required occupancies. Objectively measuring how well rooms or spaces relate to each other may be a little less straightforward but still open to analysis. Objectively evaluating how effectively a design meets the narrative intent of the client may be more a matter of critique than of measurement, but as more research is conducted into program performance this will emerge as a more objective criteria.
Structural efficiency. Structural performance is typically measured in terms of how much structure is required per unit of building program (pounds of steel or cubic yards of concrete per square foot) or as the cost of the structure as a percentage of total construction cost. A less measurable aspect of structural performance is the requirement to coordinate with mechanical and plumbing systems and with design demands for space shapes or clearances. Material choices for structure may also have an impact on thermal and acoustic performance, contributing greater or less mass to wall, partition, and floor constructions.
Weather performance. Moisture management requires exterior wall modeling and a good bit of science. Schools used to teach a graphic method of estimating temperature at various points within a proposed exterior wall construction. Currently available software analyzes not only the temperature but the amount of moisture storage capacity and water vapor migration in order to demonstrate, for all the wall components, how moisture is expected to accumulate and dissipate. This permits the software to highlight areas where moisture accumulation would be conducive to galvanic action between dissimilar metals or where conditions of temperature and moisture allow mold growth. Such modeling and analysis allow a designer to avoid these and other potential weather intrusion problems.
The consequences of poor moisture management performance are seen in building leaks, condensation inside walls or under floors, and consequent damage to building materials, increased maintenance, and shortened building life. High weather and moisture performance are generally assured through the study, adoption, and application of best design and construction practices. Increasingly, however, building scientists working with sophisticated dynamic models are better able to predict comparative performances of alternative exterior wall roof and foundation constructions. The typical metric for exterior wall performance is pass/fail, with no level of leakage tolerated; all moisture must be managed.
Lighting performance. I am writing, longhand, on a fall evening, at a public library table with eight chairs and fixed lighting provided by four 19-watt compact fluorescent bulbs in green opal glass shades. This is one table in a room containing 30 such tables. The lighting is even, glare-free, virtually shadowless, and completely illuminates the work surface. There is no glare on my writing or on my laptop screen. No light is wasted on the floor. The soft upward glow defines the ceiling above us. Additional lighting marks the entry and key architectural elements. The lighting here performs efficiently both on its own terms and with regard to energy. This lighting also performs theatrically: This place looks like a grand library reading room. By day the same room is dramatically different, being washed in daylight from tall clerestory windows above the surrounding book shelves. Lighting performance is measurable and can be modeled in virtual reality. But once lighting comfort factors have been achieved, there is a need to go beyond the numbers to achieve design intent by contributing to less measurable ambiance
Thermal comfort performance. Parameters of thermal comfort include heat, humidity, air flow, radiant temperature of nearby surfaces, individual control ability, and rate of ventilation. Modeling thermal comfort is complex, so we tend to fall back on trusted rules of thumb, rudimentary calculations, and design intuition. When thermal comfort performance is important (because it would affect office worker productivity, classroom learning, or shopper comfort, for example), we pay much closer attention to analyzing these parameters, to simulating conditions, and to assuring that comfort will be achieved. Systems such as under-floor air distribution, radiant floors, chilled beams, and displacement ventilation have been developed to provide better thermal comfort while demanding less energy in performance.
The exterior wall in severe climates plays an important part in comfort. The surfaces of large pieces of exterior window glass are radiant emitters and absorbers. One of the discomforts of old single glazing in curtain wall office buildings was that one whole wall of the office was cold in winter and hot in summer regardless of air and heating systems performance. This cold and heat was perceived through radiant heat transfer. The development of high-performance double and triple glazing maintains interior glass temperature much closer to indoor air temperature, an important aspect of better thermal comfort performance.
Indoor air quality performance. Indoor air quality is measured in terms of pollutant, particulate, and oxygen content and relative humidity. A building’s ventilation system is designed to provide fresh and re-circulated filtered air and to remove stale air. Air quality can be measured, so it can be programmed. Various design parameters can be simulated so design can be tuned to meet program requirements. And air quality can be tested in operation to assure continued delivery of the design intent.
Air quality has been shown to be one of the primary components in worker productivity and student attentiveness. Levels of ventilation and ventilation effectiveness are susceptible to change through building system adjustments and levels of maintenance. Re-commissioning is partly a process to re-tune the building’s operating systems parameters to return to the designed level of performance.
Durability and maintainability. Material, system, and component durability can be measured in terms of maintenance and replacement costs, in length of expected useful life, or in frequency of required maintenance. How much will it cost to perform the periodic repairs and replacements that every material or system will require in the course of its useful life? Standard contract forms ask the contractor to gather operations and maintenance manuals from equipment manufacturers, but how many of us assess the difference in life cycle maintenance costs by comparing the performance of alternative designs as analyzed from these manuals?
Structural durability is also measurable. Thinking of structural durability as a performance measure allows it to be brought into comparisons of whole building performance. Solid granite may make a more durable wall than concrete block, which may be more durable than steel stud construction. But stud construction may create a more energy efficient wall and at lower installed cost; however, concern for moisture control performance may make steel stud construction more coordination-intensive during detailed design and construction contract administration.
Financial performance. Assessing the financial performance of a building requires analysis in two related but fundamentally different aspects. The development pro-forma analyzes the sources and uses of capital funding. One major item in this pro-forma, construction cost, is related to the materials and systems chosen for the design. Capital budgeting is the program baseline; cost estimating, value engineering, and construction cost control are the active tools of financial performance management. A post-construction cost recap provides an evaluation of how well the project met those parts of the development pro-forma that the designer was able to influence.
An operating pro-forma is mostly terra incognita to the designer: This is the yearly budget of funds necessary for the operation of a building balanced against the sources of those funds. For example, one of the line items on the expense side of this ledger is energy cost; another is the cost of maintenance. Long-term debt interest and capital repayment also appear here as annual expenses. The operating budget thus states the relationship between investment in more expensive but better performing construction (higher debt) and lower energy demand or lower maintenance (both leading to lower operating cost). Analyzing the operating pro-forma illustrates other instances in which design might influence the relation of operating costs to capital investment: Flooring materials that require less frequent repair are worth more investment; equipment with a longer proven life can reduce the need for replacement set-asides; a commercial kitchen laid out to prepare and serve more meals with fewer staff has greater value. It is worthwhile for designers and project managers to discuss operating budgets as well as construction costs in modeling and simulating financial performance.
Financial performance is also analyzed as lifecycle cost. This is the net cost of all inputs of capital and operating expense for design, construction, operation, and maintenance throughout a time period established as the estimated life of the building — less all receipts (rents, fees, tuition, profits on operations, etc.) generated by the building and less the building’s residual value at the end of its life. Some discussion of expected life cycle returns would be a useful starting point for setting objectives for financial performance. A goal of financial sustainability might be set as breakeven or net negative lifecycle cost. That is, the building will pay for itself over its lifetime or actually have a net negative cost (i.e. return positive value, all things being considered)
Focusing on whole building performance provides a structured discussion at all phases of service. As a space and use program is being developed, performance criteria should also be developed. This will be followed by conceptual and schematic design phases in which the assumptions underlying the program can be tested and the performance criteria verified. At this stage, all members of the team (owner, designer, builder, operator) should describe the models and simulations to be performed or the references to be consulted to assure the programmed performance levels can be achieved.
Design development is the time for intensive modeling simulation and analysis to feed into the detail design and coordination process. Virtual construction modeling should begin at this time to guide considerations of construction sequencing and maintainability. The line between design development and contract documents is becoming less sharp as plans, sections, and elevations may be taken directly from digital building models. Technical specifications, critical detailing, and final detailed coordination are still the tasks of this last phase of document production. As always, the construction process needs to be observed to assure that systems and materials are installed as intended by the contract documents. Final acceptance is based on review and demonstration that the building will perform as designed.
The process model described above is adapted from the commissioning process model. That model proceeds approximately as follows (with the steps of whole building performance-based design and construction process noted in parentheses):
1. Start with owner’s program document or statement of intent (and outline the level of performance intended)
2. Provide basis of design (and state measurable criteria and standards to be met in project design)
3. Verify design (and simulate performance and demonstrate attainment of desired performance level)
4. Document design for construction (and back-check details against model inputs)
5. Verify construction (and formally document compliance with documents)
6. System startup testing (and test models with real operating data; modify performance models for future use)
7. Post-occupancy recommissioning (and conduct whole building performance evaluation; feed data into generalized/normalized databases for use in future programming; verify maintenance)
I propose this process model to get our profession as well as clients and facility managers thinking about the integrated performance of whole buildings, site plans, and interior design projects. This is worthwhile because simulation and analysis of all forms of performance will lead to measurably higher performance. Higher performance in nearly every way is more sustainable performance, so the quest for high building and site performance leads to greater environmental sustainability.
David Hancock is a principal with CBT Architects. He is a practicing architect, landscape architect, and urban designer. Hancock is a member of the American Institute of Architects, the American Society of Landscape Architects, the American Society of Civil Engineers, the Urban Land Institute, and NAIOP, and he is a LEED accredited professional. He wishes to thank the Boston Public Library for hushed workspace in which to spend evenings thinking and writing.