The Canadian Commission on Building and Fire Codes (CCBFC) has created a task group to consider the use of a new rating to address airborne sound transmission between dwelling units and a calculation tool as an additional performance-based option to determine compliance with the National Building Code (NBC). To help industry take advantage of these potential code changes, NRC is working with construction industry partners to develop an explanatory guide for the calculation method and to carry out research to obtain the required product data.
Flanking Sound Transmission Facility for characterizing flanking sound transmission paths using an automated measurement system
The changes discussed by the task group include a proposal to replace the currently referenced rating that only addresses sound transmitted through the wall or floor separating adjacent dwelling units with a rating that reflects the acoustical performance of the complete building system (Apparent Sound Transmission Class or ASTC). The ASTC is a truer measure of the actual sound level perceived by occupants, as it includes noise transmitted through wall, ceiling and floor junctions (i.e., flanking noise).
The task group recommends setting the minimum ASTC design requirement at 47 for the complete system. This would yield the same performance as if the separating element and all flanking elements together met the current minimum code requirements. The new metric will facilitate design optimization and shift the focus from the separating assembly, which in some cases tends to be over-designed, to the more critical floor-wall junction, which, without sufficient isolation, often dominates the sound transmission.
Compliance with the proposed new NBC requirements would be demonstrated using one of two options in Parts 5 and 9 of the NBC (measuring the ASTC directly or looking up acceptable constructions in tables) or using a new, third calculation option to be added to Part 5. To support the use of this calculation method, the NRC Construction acoustics group is helping industry develop design guides and software tools, as well as necessary input data.
A Special Interest Group with broad industry representation has been created to oversee the development of a guide and software tools as well as coordinate research to expand supporting data. This research will be carried out using NRC’s acoustics laboratories, including a unique North American facility for the measurement of flanking noise transmission.
By providing a more accurate way to measure and predict the acoustical performance of buildings, the proposed code changes will help designers and builders create dwelling unit assemblies with acceptable sound ratings, cut compliance costs, and reduce the likelihood of failures. A draft of the design guide is expected to be completed by March 2013. The proposed changes will be submitted for public review in fall 2013. The final proposed changes, if approved by the CCBFC, will be published in the 2015 edition of the NBC.
For more information
Industry groups wishing to participate in, and support this research, are asked to contact Berndt Zeitler at berndt.zeitler@nrc.gc.ca or 613-993-9744.
For more information on the Code change, contact Morched Zeghal at morched.zeghal@nrc.gc.ca or 613-993-9632.
