How can one demonstrate compliance?
NBC prescribes three methods to demonstrate compliance with the new acoustic requirements (Figure 2). They are:
- field measurements;
- a prescriptive procedure; and
- a design procedure.
All three methods are valid for both Part 5 and Part 9 buildings.
Field measurement
The first method to demonstrate compliance is through measurements in the finished building. ASTM E336, Standard Test Method for Measurement of Airborne Sound Attenuation between Rooms in Buildings, describes a method to measure the ASTC rating directly. The advantages of this compliance path are one does not need to know all of the construction details of the building under evaluation and the measurements are straightforward. The results are a true representation of the sound insulation of the building under test, including the effects of any construction deficiencies. The disadvantage of this compliance path is it can only be used once the building has been built. Any subsequent changes to the construction as a result of unsatisfactory sound insulation will likely be costly.
Prescriptive procedure
The second method to demonstrate compliance is by following a set of solutions prescribed in NBC. The advantage of this compliance path is that it is easy to use. As long as the instructions in NBC are followed, the finished building is deemed to comply with the required sound insulation rating of ASTC 47.
The first part of the prescribed solutions considers the separating wall or floor. The assembly must have an STC rating of at least 50. This connects the new acoustic requirements with the mandates in previous editions of NBC, and allows designers and architects to continue to use established wall and floor assembly designs.
The second part of the prescribed solutions concerns the building elements connected to the separating element. For these adjoining constructions, NBC provides a simple set of requirements. For example, the requirement for adjoining constructions in heavy homogeneous structures (such as concrete) is given in terms of a minimum mass per unit area. For lightweight wood- or steel-framed constructions, one of the requirements for adjoining constructions is simply the gypsum board at a wall-wall junction is not continuous. The appendix of NBC also includes several tables with detailed examples of constructions that are deemed to comply. While the list of examples is limited, optional modifications—expected to yield similar or better ASTC ratings—are provided.
A disadvantage of this compliance path is it does not yield ASTC values, but instead provides a pass or fail mark. Building professionals who are interested in achieving better sound insulation than ASTC 47, or who want to use designs that are not part of the prescriptive procedure, cannot demonstrate the actual ASTC rating when employing this compliance path.
Design procedure
The third method to demonstrate compliance is based on the International Organization for Standardization (ISO) 15712, Building acoustics – Estimation of acoustic performance of buildings from the performance of elements – Part 1: Airborne sound insulation between rooms, which describes a method of predicting the apparent (= total) sound transmission if the details of the building construction are known, and laboratory test data is available for these details (The International Organization for Standardization (ISO) 15712, Building acoustics – Estimation of acoustic performance of buildings from the performance of elements – Part 1: Airborne sound insulation between rooms, has recently been revised and assigned a new designation, ISO 12354-1:2017. NBC currently references the standard’s 2005 edition.). The general concept as illustrated in Figure 3 is to predict the structure-borne noise transmitted through each flanking path, and then to combine the contributions from each path to determine the apparent sound transmission. The importance of each transmission path depends on the construction details of the separating partition and the adjoining building elements and their junction.
An advantage of this compliance path is it allows the estimation of the expected sound insulation for building configurations at the design stage, including a cost-benefit analysis. Building elements needing to be modified for better sound insulation and over-designed elements (where cost-savings are possible without affecting the sound insulation) can be identified. The disadvantage of the design procedure is it involves more effort than the prescriptive method and requires laboratory measurement data for flanking sound transmission. If data for the specific construction detail is not available, then the procedure cannot be used.
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