Performance-Based Building Code - Decrypting Potential Challenges to building professionals
Author: *Avinash Gupta, P.Eng.; CBCO, CRBO, LBO; Mohamed Mohamed, P.E., P.Eng.; Dominic Esposito, P.Eng.
In Canada, efforts are in progress to transition National Building Code of Canada (NBC), which contains primarily perspective requirements, to a performance-based code which would specify performance criteria. How can our professionals prepare for this?
This article explores potential challenges in the transition to a performance-based code with a focus on the code's fire and life safety aspects.
Evolution from Prescriptive to Objective-Based Code
Where adopted, for the design and construction of buildings, all requirements NBC must be complied with, either prescriptively or by other means that provide at least the minimum level of performance intended by the code. The prescriptive requirements in the code are called acceptable solutions.
NBC 1995 was replaced in 2005 by an objective-based code. An objective-based approach stipulates the overall objectives that are required to be met, with consideration of the minimum performance intended by the application of the acceptable solutions of the code. NBC also includes functional statements and intent statements to assist the code user with understanding the reasoning behind the acceptable solutions.
The objective-based NBC was introduced to provide options to designers to either meet acceptable solutions/prescriptive requirements of the code or provide an objective-based alternative solutions to achieve at least the minimum level of performance required by the code. The introduction of an objective-based code was a step to transition towards a performance based code to enable alternatives to prescribed code requirements. A designer must note that some provisions (acceptable solutions) in the current code are already performance-based; for example, NBC Part 5 of Division B, dealing with 'Environmental Separation' is entirely performance-based.
A non-prescriptive approach is an alternative solution, and the proponent assumes the responsibility for code compliance. The person developing an alternative solution approach must demonstrate to the Authority Having Jurisdiction (AHJ) that the proposed alternative solution achieves the overall minimum level of performance intended by the code.
The performance-based building design concept is not new. One of its first implementations was in the Hammurabi's Code (c. 1795 to 1750 BC), which stated that "a house should not collapse and kill anybody." The current practice is to ensure that the minimum prescriptive requirements included in NBC are met in the proposed design, so no modelling or verification tools are needed for the building design. In contrast, performance-based building design is an innovative approach to design, construction, management, and maintenance of buildings and to accommodate greater flexibility in designing and selecting materials.
The International Council for Research and Innovation in Building and Construction (CIB) in 1982 explained the definition of the performance-based building approach in its report, “Working with the Performance Approach in Building”, Publication n. 64; it stated that "the performance approach is, first and foremost, the practice of thinking and working in terms of ends rather than means. It is concerned with what a building or building product is required to do (i.e., must do), and not with prescribing how it is to be constructed”. Thus, a performance-based design is no more than understanding the function of the proposed building and its components using resilient, meticulous, and consistent scientific tools. It means that all parts of the building must be subjected to scrutiny when developing a performance-based design.
The designers must understand that the prescriptive requirements or specifications are different from deciding and defining performance criteria or qualitative performance requirements of specifications. Prescriptive requirements are embedded in NBC; thus, they are easier to deal with than performance-based requirements; however, they may not be the most desirable and economical solutions for building design. On the other hand, performance-based approaches may employ better, innovative, or cheaper solutions without compromising the required level of quality and safety.
Although prescriptive specifications may not be ideal, they will continue to play a significant role as adequate knowledge for some performance features is not available; therefore, building specifications will often need to be expressed partly in performance terms and partly prescriptively. Other motivations for retaining prescriptive requirements are, for example, the cost of a performance evaluation of a product in comparison to its price, scarcity of professional resources, skilled labour and contractors or the absence of a local construction industry to construct a complex performance-based design in the remote parts of Canada.
Furthermore, significant efforts are required for designing a building based on its performance so that adequate safety of the occupants and property protection is achieved. The design should state the level of performance required that can be projected from experiments, calculations, or modelling.
Requirements of Performance-Based Designs
Preparer and Reviewer Qualifications
The qualifications, training and experience required for the designers who develop performance based designs are not explicitly specified anywhere. No formal certification or educational training program exists that identifies a person capable of skillfully creating performance-based designs. Thus, a registered and licensed professional engineer/architect could do performance based designs until the provinces and territories decide the required qualifications. As mentioned earlier, the AHJ plays a pivotal role in assessing the methodology, specific desired levels of safety, fire scenarios, safety factors, etc. adopted for developing a performance-based design; therefore, the qualification, training, and experience of AHJs are of importance for approving performance-based designs.
With respect to fire and life safety performance criteria, the Society of Fire Protection Engineers Handbook (SFPE) provides a framework of performance criteria essential to provide an agreeable level of risk to the occupants of a building. For example, one of the criteria for measuring the performance of a building is the safe evacuation of occupants before the environment becomes untenable in a fire emergency.
An alternative solution is usually developed for a specific design requirement to meet the intent of the code through the associated objectives, functional statements and the minimum performance intended by the code. Whereas, for a performance-based design, the design team chooses the fire safety criteria (in consultation with the AHJ) based on the overall intended performance of an adopted code/standard. The fundamental prescriptive requirements embedded in the adopted code, standard, and local bylaws will constitute a part of the performance-based design. The design input ingredients for developing a performance-based design may include various elements such as selecting fire and life safety evaluation criteria, occupant characteristics/use(s), proposed building design parameters, fire scenarios, type of construction and specifications. Once the design input is completed, it is used as data for the verification method(s) to obtain design output. The result, thus, achieved is compared to the fire and life safety criteria to determine if the proposed design satisfies the criteria.
Application of Performance-Based Design
The performance-based design approach provides design flexibility; however, at this point in time, it does not and cannot replace the current model code. An example given below provides a flavour of a performance-based design. A 50-storey building is proposed to have the uppermost floor with 500 occupants as it contains an observatory and a nightclub. With the uppermost floor located 150 m to 160 m above grade, the most apparent concern is the safe evacuation of all occupants.
NBC requires at least two remotely located exits, adequately sized to serve the occupant load, arranged so that they are clearly visible, identifiable, and always accessible. The building height and the occupant load undoubtedly suggest that compliance with NBC provisions would require many more exit stairs or wide exit stairs from the uppermost floor to the grade level. Therefore, complying with the acceptable solutions of the code is not only a challenge but may be impractical. Hence, a performance-based design is a better approach for such complex buildings.
Ultimately, the building is designed with refuge floors; therefore, a reasonable strategy would be to move all the occupants to refuge floors before they are evacuated. Another or complementary possible solution to address evacuation during a fire scenario could be provisions for highspeed elevators with additional fire and life safety features. However, if elevators are not operational or out of order, this must be considered in the evacuation strategy.
For demonstrating the safe evacuation of all occupants, available safe egress time (ASET) and required safe egress time (RSET) are essential to assess a fire scenario.
The above-stated performance-based design proposal would be reviewed by the AHJ to examine if it meets the fire and life safety criteria decided for the project while significantly departing from the prescriptive fire and life safety requirements of the code.
Discussion and Conclusion
This article is limited to gauging the impact of performance-based design on building professionals. It does not cover all aspects of a performance-based design because of its complexity. However, this article has made an attempt to set the ball rolling, prognosticating the potential challenges that could inadvertently trip the building industry.
A performance-based design might be practical for a structure, especially when, due to its configuration, it is technically not viable to meet the prescriptive requirements of the code. In the current code, to develop an alternative solution, the objectives and functional statements must be considered which do not provide explicit quantified measures of performance, whereas, in the case of a performance-based design, the designer must meet a pre-decided set of performance criteria complementing the fundamental provisions of the code. One of the conspicuous purposes of performance-based design is to motivate the development of inter provincial and intercontinental trades. And the main design area where performance-based design and procurement could be considered are service engineering, energy consumption, for example, lighting, indoor climate-heating, ventilation, and air conditioning (HVAC), air quality, and plumbing.
The immediate, and visible concern is the role of the AHJ in reviewing and approving a performance-based design proposal. Currently, most jurisdictions hire building officials who must pass all the code exams required by their jurisdiction or are professional engineers; however, they may not be necessarily qualified to validate complex analyses such as time-based egress analysis or (and) smoke modelling- two of the most essential components commonly required for managing a fire and life safety performance-based design. Furthermore, there are few professionals who can decode complex time-based egress analyses and smoke modelling, thus making its adaptability scarce.
For developing a performance-based design, the significant challenge is how to predict the performance of a building constructed based on it. Predicting the performance of a building is feasible by developing education and training modules for design professionals that could include showing where, what, why, and how the concept is already being put into practice with examples and explanatory notes. In addition, organizing internal and international seminars and workshops for educating professionals and building officials, generating guidelines for performance-based buildings, providing clients/designers with decision-making/assessment tools, and developing a few varieties of pilot modules for an electronic education system.
For the long-term perspective, a mandatory semester on performance-based design in the engineering/architectural curriculum at universities/colleges could be included.
It is of utmost importance to discuss a performance-based design for any project with the AHJ before committing to the design, as many municipalities do not entertain alternative solutions. Finally, resilient, and reliable documentation of a performance-based design negotiated and agreed upon between the design professionals and regulator(s) must be retained at a conspicuous and pre-notified location for the lifetime following building construction- essential information to a forensic team to investigate the reasons for a failure.
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*All the writers are experienced professionals and currently working in the building code industry. The views expressed by the authors are for educational purposes only.