Thinking Inside the Box: The Case for Post-Occupancy Evaluation
Although sustainability continues to grow as an industry-wide priority, post-occupancy evaluation (POE)—a critical step in the sustainable design process and an important tool in advancing high-performance building solutions—remains drastically underutilized.
Building occupants are an essential source of information on building performance and design effectiveness, yet architects rarely take the time to ask their opinion. Even the U.S. Green Building Council is content to measure high-performance buildings with its Leadership in Energy and Environmental Design (LEED) green building rating system based on "as-designed" performance.
After years of feeling awkward when clients ask us how our buildings perform after they are complete, we at HOK have initiated a program to address this important issue. Based on our experience, we have concluded that not only do post-occupancy evaluations provide valuable information for the facility owners, contractors, engineers, and designers, but also that the widespread implementation of POEs is absolutely critical for the continued advancement of the sustainability movement.
Results of the study challenged our preconceived notions concerning many of the most common sustainable design strategies. While occupants expressed a high degree of satisfaction with having greater access to natural light, for example, some respondents also reported problems with light spill and glare. We learned that the spaciousness provided by open office design—generally lauded by clients—often leads to problems with acoustics and visual privacy. While this may not seem to be a sustainable design issue, it is an issue that has a profound impact on the day-to-day experience of people within their buildings, and therefore colors their perception of the building as a whole.
Our study also revealed that the energy savings outlined through energy modeling in the design phase do not always translate into the same degree of actual operational savings, particularly if vital process steps (commissioning, value engineering, follow-up energy modeling, etc.) are omitted.
Perhaps as important as our results, we also learned that conducting a POE can and should be a relatively simple, painless process. Available tools, such as the Center for the Built Environment (CBE) Occupant Satisfaction Survey, make gathering and analyzing a broad range of user feedback a simple matter of consultation. Additional measurements of energy performance and end-user interviews added an important dimension to the study with relatively little investment of time and cost. It has become clear to us that the benefits to be gained from POEs far outweigh the effort needed to conduct them.
How HOK’s POE process works
To gather sufficient data, we evaluated nine successful green building projects representing a cross-section of client types and project types. The POE sample includes two office buildings, three labs, two interiors projects, and two education facilities. Three of the projects are LEED certified, and all nine have garnered some type of distinction for their sustainable qualities, such as winning a Top Ten Award from the AIA’s Committee on the Environment.
The evaluation method included the CBE Occupant Satisfaction Survey, an energy evaluation, and user interviews. The goal was to learn how occupants were responding to the buildings and if design goals established at the outset of the projects were being realized.
In general, clients expressed a high level of satisfaction in HOK green buildings, and sustainable features have significantly enhanced building operations. There were strategies that left room for improvement, however, and it is in these areas that the POEs were most valuable. The knowledge gained has enabled us to help owners address existing problems and to apply lessons learned to current and future projects. As a result, HOK has strengthened its relationships with clients and partners and is more equipped than ever to deliver on the sustainable results it promises.
The CBE Occupant Satisfaction Survey, which takes building occupants 5-12 minutes to complete, is a Web-based survey tool that provides a standardized database of responses. Accumulated data includes more than 27,000 respondents from some 200 buildings, both sustainable and conventional projects. The survey offers benchmark comparisons of building type, size, and year and evaluates design features ranging from indoor air quality to lighting to acoustics. (For more: www.cbe.berkeley.edu/research/survey.htm.)
The energy evaluation sought to compare design analysis with actual data using utility bills and maintenance records. To ensure accuracy, a third-party expert, Architectural Energy Corp., Boulder, Colo., was hired to carry out the process.
The end-user interview was included as a means to generate more-detailed data than that available through the CBE survey. Participants were asked questions about specific sustainable solutions (What is/isn’t working? Why?), occupant feedback (What are the building features that have had a very positive or very negative reaction? Why?), and an overall appraisal (Have design goals been met? What was your greatest surprise? What was the building’s greatest success?).
Reviewing the major findings
Overall, we gained confirmation that end-user satisfaction in HOK green buildings is quite good. According to the CBE survey, all HOK green projects finished with scores indicating a higher degree of satisfaction than dissatisfaction, and the majority of them recorded scores in the upper half of all buildings surveyed. Specific results are presented within four categories: workplace, resources, placemaking, and values.
Each of the categories surveyed as part of the standard CBE occupant satisfaction survey (indoor air quality, thermal comfort, lighting, acoustics, office layout, and office furnishings) has an impact on the quality of the workplace. While satisfaction was generally good in all of the HOK surveyed buildings, the trends discovered in the evaluation of individual measures were telling. For example, all projects recorded satisfaction scores way above average for air quality, while all but one project recorded extremely low satisfaction scores for acoustics.
For thermal comfort, however, there was significant variation among buildings. It is interesting to note that the buildings with the most successful energy-efficiency strategies also scored highest for thermal comfort.
Access to natural light is understood by designers as a universally positive feature; however, we found that user satisfaction requires a true integration of daylighting strategies with the building’s lighting systems. In some of our highly successful daylit buildings, challenges remain with light spill and glare, and results point to operational problems with some occupancy sensors. CBE confirmed that their evaluation of green buildings also showed a surprisingly high number of projects with light spill and glare undercutting the success of daylighting design solutions.
The open office environment, a mainstay of many sustainable workplace projects, presents its own set of challenges. Many of those surveyed expressed a real concern about visual privacy and the ease of interaction with colleagues and clients. Contrary to popular belief, we found that open office environments were generally more challenged than closed office environments to meet collaboration and interaction goals successfully.
The issue of speech privacy generated an even higher degree of sensitivity, as satisfaction scores in acoustics were lower than in any other category. Interestingly, these low scores were reported in both open and closed office environments alike. It is clear that acoustics, a building component commonly not featured in sustainable design discussions, deserves renewed attention.
Through an analysis of resource consumption, we learned that actual energy use in the buildings was generally greater than the modeled energy use, even though the peak electricity demand was generally less than the anticipated peak demand. From the data we collected, we were able to draw the following conclusions:
• The value of commissioning is clearly evident and cannot be overstated. Projects with minimal or no commissioning reported higher energy usage. Owners who did not commission said they would reconsider that decision in the future.
• When a disconnect existed between MEP engineers and sustainable design consultants, it resulted in higher energy usage.
• Most successful projects performed energy analysis early in the design phase and repeated analysis as design progressed.
• Some projects suffered from value engineering changes at a late stage.
Placemaking efforts have been enhanced through creative site development strategies. The buildings surveyed have established unique identities while remaining consistent with the surrounding landscape and communities. We did find that maintenance of non-traditional landscapes required commitment on the part of the owner. While these environments were beloved and provided substantial operational cost savings, they were features that required careful attention to establish successful maintenance routines.
Of all categories, adherence to values represents the greatest success and the greatest driver of sustainable solutions. Users take great pride in working in environmentally friendly facilities, and companies see sustainable design as a positive reflection of their core values. Owners state that the green features of their buildings provide visiting clients with a favorable impression and often serve as the first topic of conversation.
A call for POE industry-wide
Through this study, architects, engineers, contractors and facility mangers alike have gained a greater understanding of sustainable design and the operation of high-performance buildings. It is clear that this small sampling of projects provides only a glimpse of what might be learned through industry-wide adoption and implementation of post-occupancy evaluations.
At this critical stage in the sustainability movement, just as green building is entering the mainstream, we cannot afford to ignore shortcomings. When high-performance sustainable buildings are improved through careful attention to lessons learned, the results will be even more compelling. Resolution of the industry-wide disconnects between design expectations and actual performance will validate our work and encourage continued innovation and widespread acceptance of green building practices. The time is now for POEs to become standard industry practice. BD+C
Sandra Mendler, AIA, is Sustainable Design Principal at HOK, a global architectural design and services firm. Based in San Francisco, she is co-author, with William Odell, FAIA, and Mary Ann Lazarus, AIA, of
The HOK Guidebook to Sustainable Design, Second Edition (John Wiley & Sons, 2006).