Specifying Ends and Means
Performance-based specifying can foster teamwork, pushing the building team beyond satisfying minimum requirements
The term performance-based is commonly used to describe codes and standards that seek to define the purpose and scope of a building system, without specifically prescribing its details. Performance-based specifying pushes the concept a step further, using it to describe the nature of the actual specification that an engineer writes.
'The difference between [performance-based] codes and specifying is that codes refer to the regulatory part,' says Jon Traw, P.E, president of the International Conference of Building Officials. 'Specifying is outside the regulatory. It's an owner-builder-supplier relationship.'
In fact, a project design could, for example, rely on performance-based design without using performance specifications. 'You could have a project with performance-based design, but just standard prescriptive specs,' explains Dan Gemeny, P.E., a vice president at The RJA Group's Los Angeles office. 'We tend to write performance specs for fire systems. But in the fire alarm industry, it's not atypical for system vendors to go to the engineering house and sell their equipment. In fact, it's typically a proprietary spec,' says the consultant.
Peter Bohn, P.E., chief mechanical engineer at The Austin Company's Schaumburg, Ill. office, provides another perspective distinguishing the difference between performance and prescriptive specifications: 'There isn't any spec out there that's one or the other,' he says.
Bohn suggests that a prescriptive specification that uses any performance basis at all becomes a performance-based spec. 'If you have to make a mix, then it becomes a performance-based thing,' says Bohn. Codes to specs
There is, of course, an overlap between codes and specifications, and applying the term 'performance-based' to both is not new.
With respect to codes, the United Kingdom, Australia and New Zealand have been using performance-based standards since the early 1990s. U.S. code organizations started looking seriously at these concepts in the mid 1990s, even though the National Fire Protection Association's 2000 Life Safety Code was probably the first U.S. code to use the performance-based approach.
Actually, building codes in the United States, while being largely prescriptive, for many years have already incorporated the equivalency concept that allows for cost-effective and flexible alternatives. Traw suggests that, traditionally, U.S. codes were fairly unique in this respect. However, he adds that these code provisions are different from a true performance-based system of regulatory codes.
'Performance-based code changes existing codes in a way that clearly defines the intent before providing the solution; they separate intent from means of compliance, broadening the range of possible solutions,' he says.
Two arguments, advanced by Traw and others, may well point to the greatest advantages of performance-based specifying. First, performance-based specifying encourages design professionals to look beyond the minimum standards of the prescriptive codes. Second, it is a means to bring members of the building team together, enabling them to agree on project goals up front, before any design even takes place.
Building Systems Design of Atlanta is the creator of a performance-based specification software system called PerSpective, which was developed for the Construction Specifications Institute and Design-Build Institute of America. Illustrating the performance-based need for 'teamwork,' BSD President Robert Dean claims that the users of the software include all the various members of the building team: owners, who might be government agencies, large corporations or any private company with a sizable building program; contractors; architects and consulting engineers.
He also suggests that it's the engineer who has the most experience with performance-based specifying, because engineers-especially mechanical engineers-are more accustomed than architects to dealing with performance specifications.
'Performance-based specifying is a means of establishing the required performance of a building, or its elements, before it has been designed,' says Dean. 'This is why it is important on design-build projects, where it is necessary to set the quality early in the building project.'
Traw explains that the approach creates a methodology that brings parties together for a meaningful discussion, where the needs of the owner come to the fore. Dean offers the example of a school project.
'An owner goes to a design-builder and says, 'I need a building of so many square feet,'' says Dean. 'The owner may have a program-knowing how many classrooms he wants, and that a gymnasium is needed-but he is not in a position to say how it performs with respect to energy requirements, lighting and the like. The PerSpective software was designed to allow an owner to specify, in advance of the design, how his completed building needs to perform.'
In addition, the software allows design professionals to show the owner what kind of building they are proposing to build, before they even have a design-even before they know what systems will be included. Holistic specifying
Performance-based specifying might better be termed the 'whole building' approach to design: 'Some people look at structural, egress or fire-resistance separately, instead of looking at the interrelationship,' says Traw. 'But we need to look at what impact a redundancy in the structural system has on the egress system, for example. Performance-based design, if properly put in place, promotes the holistic approach.'
This is notable, Traw explains, in that no one model applies to every project. For example, the owners of a semiconductor plant, which can be severely affected by a serious power event, may request a performance level much greater than the minimum required by regulatory codes.
Dean concurs: 'Codes may require a certain number of water closets, but an owner might say, 'I want more.' So, in areas where codes do not offer specifics, performance-based specifying becomes an even more important factor.' Defining specifications
Another benefit of the performance-based approach is that a specifying engineer determines the results that are to be achieved, while leaving the system designer or contractor considerable latitude in defining the system. In other words, the specifier fires some parameters, while leaving others open to accommodate a more flexible approach.
Furthermore, whether discussing codes and standards, or addressing the issue of specifications, it would be a mistake to suggest that a performance-based approach precludes use of the prescriptive.
With respect to code-making, within many jurisdictions that have adopted a performance-based approach, there are still cases where the prescriptive codes make more sense. And one can make the same argument about using performance vs. prescriptive specifications: specific projects-and particular systems-may call for one or the other.
'Even in countries where performance-based systems have been put into place,' says Traw, 'they have been limited to a certain number of buildings and structures.'
'In many cases,' he says, 'the judgement is that prescriptive design is close enough. So there is no need to debate the system design. Prescriptive standards are not thrown away. They just become one possible alternative.'
In the U.S., Clark County, Nev., which encompasses Las Vegas, is a good example of how-depending on the unique needs of a project-either performance-based or prescriptive codes may be used. As Traw explains, the size and complexity of large hotel complexes like the Bellagio make performance-based design the suitable approach. 'You could not build Bellagio if you adhered to the prescriptive provisions,' he says. 'You would have to go into the administrative alternatives.'
Philip Spagnolo, vice president of mechanical engineering at McClier, Chicago, contends that a project doesn't have to be complex to take advantage of the benefits of performance-based specifying. A single-story office building is just as good a candidate, he says, or a simple tenant improvement project would work in cases 'where the building engineer at an existing facility is familiar with the systems and could help write a performance spec with respect to lighting, HVAC, electric, etc.'
On the other hand, Austin's Bohn offers some examples of building projects that may rely on more descriptive specifications: 'I suppose there are manufacturing processes that require something more prescriptive,' says Bohn. For example, he says, schemes for doing office buildings are pretty well set.
'Most offices function about the same electrically. Research laboratories, however, are an example of where the systems are not so set. In certain types of facilities-data centers and research labs-you must tell them what you want to do. Part of the prescriptive approach is how much feedback is required,' says Bohn.
Performance-based specifications allow specifying engineers to define the parameters and goals of a system, Bohn further explains, while leaving the details to a system designer who specializes in this area. A building owner, in this way, receives the advantage of greater flexibility and more options as a result.
But the extent to which this is the case depends on the type of project. For example, if the project calls for the installation of a new, highly-integrated building system from a single vendor, a performance-based specification might be the choice. But for a retrofit or expansion project, it would make sense to use a prescriptive approach because of the need to interface with existing systems.
In applying the concept of performance specs to particular systems, Bohn points out that there are certain types of equipment for which the need to provide greater detail makes prescriptive specs more appropriate. 'You need to be more careful about motors. There's a very wide set of options, and performance specifying motors can be dangerous. It requires more care, and engineers need to get very specific.'
One pitfall with prescriptive specifications is that the specifier must have a detailed understanding of the system. In the past, a P.E. knew how to write the specifications for a pneumatic controls system. But today, with the advent of sophisticated electronic circuitry, it is not always the case that a P.E. knows the details of modern automated building systems.
Control systems, in general, have seen a significant application of performance specifications. 'Controls always will be different from other parts of engineering,' says Bohn. 'Their task is at times abstract. To get a control system, you need to tell it exactly what to do.' Fear of change, increased liability
Not everyone embraces this trend, and in fact, there are signs of resistance in parts of the engineering community. (See 'Performance-based Specifying Has Its Detractors.')
Traw claims this is simply resistance to inevitable changes in the ways engineers practice: 'Change is always uncomfortable for some, especially for those engineers who feel a real or perceived liability. There probably is some added liability, and the onus is on the designer to do a much better job,' admits Traw. 'They can't say 'the codes made me do it.' An increase in liability might be an increase in responsibility.'
No matter how design professionals feel about it, performance-based design appears to be part of the future. Performance-based approaches to building design will not completely supplant the use of prescriptive specifications, but on many projects, it makes a lot of sense and can lead to significant savings in time and money for building projects-ever important criteria to owners.
Performance-Based Specifying Has Its Detractors
While performance-based specifying has generally been accepted in the professional engineering community, there are at least a few P.E.s who take issue with it. One outspoken critic is David Exe, P.E., president of Industrial Engineering Inc., Woodbury, Minn.
Exe doesn't have a problem with performance specifying per se. Rather, he feels that many P.E.s are doing performance specs and selling them as design-at design prices.
'Performance specifying is a way for design professionals to pawn off their design responsibilities,' charges Exe. He argues that engineers write performance specifications and the subsequent design is performed by unlicensed designers, which is 'probably the greatest single problem undermining the engineering profession today.'
However, Pete Bohn of The Austin Company points out that, in many cases, a prescriptive specification would be a waste of time: 'In our brand of engineering, it's a matter of assembling pieces correctly. We set the performance requirements. We don't always need to describe what bolts to use, or that something needs to be five ft. deep.'
However, Philip Spagnolo, vice president of mechanical engineering at McClier, Chicago, does point out a case that lends credibility to Exe's claim: 'I lost a sizable job to another engineer who underbid our fee. The other guy's number was less than half our fee, but he left a lot of the burden of design on the contractor, and the owner was faced with many change orders.'
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