The 2015 editions of the National Model Construction Codes are presented in an “objective-based code” format that is structured in three Divisions (A, B and C). The Codes contain explicitly defined objectives and functional statements (see Division A), which are statements on the functions that the components of a building or facility must perform and the objectives that these functions must satisfy. Most of the Code provisions in Division B—called acceptable solutions—are linked to at least one of those objectives and functional statements. The sets of objectives and functional statements are referred to as “attributions.”
The attributions are developed through a process called “bottom-up analysis,” which involves the analysis of each provision in Division B of the Codes to determine its intent and then derive the applicable objectives and functional statements. The bottom-up analysis is carried out by the standing committees of the Canadian Commission on Building and Fire Codes (CCBFC) with extensive support from the staff of Codes Canada at the National Research Council of Canada (NRC).
Intent statements serve explanatory purposes only and do not form an integral part of the Codes. They contain useful information not available elsewhere that helps Code users understand the rationale behind each requirement. This contributes to a more accurate interpretation and application of acceptable solutions and a clearer understanding of what alternative solutions should achieve.
The intent statements are included in the electronic versions of the Codes and are available for viewing by users of the printed versions of the Codes through the Codes-Guides Library.
Only the provisions in Parts 3 to 9 of Division B of the National Building Code of Canada (NBC) (excluding the explanatory Notes) have intent statements.
Clicking on a Sentence reference in the left-hand portion of the screen brings up an analysis window on the right-hand side, which contains that Sentence’s applicable attribution(s) and intent statement(s).
For the most part, entire Sentences are analyzed as units of text. In such cases, only the Sentence number is identified in the analysis window, and the actual text of the Sentence can be found in the Code. In some instances, however, the analysis applies to only a portion of a Sentence; in such cases, the Clause or Subclause being analyzed is identified in the field entitled “Attribution,” or the portion of text being analyzed is quoted or summarized in that field and introduced by the phrase “Applies to.”
The objectives attributed to the provisions or portions of provisions in Division B are derived from the bottom-up analysis. Each analysis window contains tabs displaying the acronyms for each objective attributed to the text being analyzed (e.g., OH1). Clicking on a tab reveals a panel containing the information related to that objective attribution.
Some provisions or portions of provisions in Division B have no objectives attributed to them. In such instances, the analysis window will contain a tab displaying the symbol “+” rather than an objective acronym.
The specific functional statements and sub-objectives attributed to the text being analyzed are presented in square brackets in the Attribution field. If the attribution(s) and intent statement(s) apply to the entire Sentence, no explanatory text will appear before or after the square brackets; if they apply to only a portion of a Sentence, the square brackets will either be preceded by the Clause or Subclause identifier, or followed by a phrase beginning with “Applies to,” which specifies which portion of the Sentence the attribution(s) and intent statement(s) apply to.
An intent statement explains the purpose of a provision or portion of provision found in Division B. It reveals what the standing committee was trying to achieve by introducing the Code provision in the first place or what the Code-user community has come to understand as the reason for the provision’s existence.
Generally speaking, intent statements present the consequences of non-compliance with a requirement using a standardized set of phrases and terms. They try to answer the question “What are the undesirable thing(s) that might happen if this provision is not complied with?” In many cases, the initial consequences of non-compliance may lead to a chain of consequences; the link between those consequences and the overall objective of the provision may only become apparent in the description of the latter consequences in the chain. All functional statements and objectives identified in Division A and attributed to the provisions in Division B are derived from the intent statements.
Not all Code provisions are technical requirements; some act as definitions, clarifications, application modifiers or pointers to another provision. In such cases, the intent statement explains the role the provision plays in the Code, and there is no chain of consequences. These types of provisions have no objectives or functional statements attributed to them. Note A-22.214.171.124.(1) in Division B provides information on how these types of provisions are interpreted.
Many of the hazards and undesirable events the National Model Construction Codes address, such as deterioration, spread of fire and heat loss, can only be minimized, retarded or controlled through compliance; other undesirable events, such as the ignition of fire or structural collapse, can never be prevented with absolute assurance. This is why the phrase “to limit the probability” is used in the intent statements rather than “to prevent.”
Using the phrase “to prevent” would mean that it is possible to comply fully with a requirement but still not meet its intent. The phrase “to limit the probability” was therefore adopted to clearly convey the notion that the Codes do not and cannot provide absolute protection.
In the development of the intent statements for Part 5 and Part 9, it was recognized that:
Describing the logical progression of consequences—from the basic property or performance issue addressed by the provision through to the objectives—resulted in intent statements for some Part 5 and Part 9 provisions that are longer and more detailed than those for provisions in other Parts of the NBC.
Furthermore, some building elements addressed by Part 9 provisions may serve a variety of functions depending on the design of the building. In these cases, intent statements were developed for each function that the building element might serve.
Virtually all components of a building will eventually fail in the absence of maintenance, and many will eventually fail even with maintenance. This normal, expected failure cannot be addressed by Code provisions. However, many NBC provisions do address premature failure—failure that occurs at a time when the component would be expected to continue to perform its function without special maintenance. These provisions do not specify an expected service life (i.e., acceptable lifespan) for a material, component or assembly; in general, they prescribe performance criteria, material properties or service conditions that are expected to provide a reasonable service life (e.g., material type, thickness of a protective coating, or minimum temperature of air contacting furnace heat exchangers). Only Sentence 126.96.36.199.(1), Clause 188.8.131.52.(5)(b) and Sentence 184.108.40.206.(5) of Division B refer explicitly to service life or to a time period over which a component is expected to perform, without stating a precise minimum period.
The intent statements for all provisions that promote resistance to deterioration describe the consequences of premature failure that would result from failing to comply with the respective requirement.
All intent statements describe the initial consequences of non-conformance with a Code provision. Many intent statements also describe a chain of consequences in cases where posterior consequences may be more severe than the initial hazard. One such scenario is the failure of environmental separation elements.
Many hazards that could result from non-compliance with Part 5 and Part 9, such as condensation and the ingress of precipitation, would not only initially lead to adverse health effects but might also lead to the eventual deterioration of building elements, which could, in turn, lead to a multiplicity of negative effects on the performance of required environmental separation elements. Rather than including a detailed description of each and every specific potential effect in the applicable intent statements, the Standing Committee on Housing and Small Buildings and the Standing Committee on Environmental Separation chose the phrase “which could lead to compromised integrity of environmental separators” to capture the concept of broader adverse performance implications.
Because environmental separators provide protection from issues like water ingress and condensation, they protect structural elements from rot, corrosion and conditions conducive to the infiltration of destructive insects. Consequently, most Code provisions dealing with environmental separation elements have a structural safety intent and objective as well as a health intent and objective.
Other scenarios involve environmental separation elements that also have a structural role and structural elements within environmental separators. In addition to describing the potential direct consequences of loss of structural integrity or structural collapse, the intent statements also describe the chain of consequences that would occur if only the environmental separation function were compromised. A comprehensive analysis of all these compromised functions would, however, increase the volume of text to such a degree that the standing committees decided to summarize the multiplicity of consequences with the phrase “failure of required environmental separation elements.” Thus, many Code provisions that mainly address structural issues also have health objectives stemming from the failure of required environmental separation elements.
In many intent statements related to Objective OH1, Indoor Conditions, negative effects beyond the initial consequences of non-conformance are identified in sets of short bulleted lists rather than in continuous, full-length sentences. Each item listed represents a consequence that is as likely to occur as another at this point in the chain of consequences. There is no direct correlation between the order in which the consequences are presented in these lists and the order or certainty of their occurring; each consequence identified in one set will potentially lead to at least one of the consequences in the subsequent set. This approach using simplified lists was implemented to improve the readability of the intent statements and to reduce their length.