25 Apr The 2018 BC Building Code Encourages Better Acoustics in Multi-Family Dwellings
Back in 2015, updates to the National Building Code ushered in new acoustical requirements for sound transmission between adjoining suites. While previous iterations of the code set criteria for direct sound transmission through separating wall, ceiling, and floor assemblies, as quantified by an assembly’s sound transmission class (STC), the new code regulates flanking noise. As its name suggests, flanking noise is the sound that travels around a partition—through adjoining or perpendicular walls, ducts, hallways, windows, and even structural components. The new code sets criteria for a separating partition’s apparent sound transmission class (ASTC) rating, a metric that encapsulates both direct and flanking noise.
Over the past few years, the requirements of the updated national code have been trickling down to the provincial building codes. In BC, they took effect on December 10, 2018, with the new provincial building code.
STC Versus ASTC
Because an assembly’s STC rating is set in controlled test conditions, real-world performance rarely lives up to lab-derived ratings. “The previous code encouraged developers to over-design partitions as a way of accounting for the variance between the laboratory and reality,” explains Paul Marks, one of our principals here at BKL. “When reviewing building plans, it’s not uncommon for us to see partitions rated as high as STC 55.”
Yet overdesigning to meet code on a wall-by-wall basis isn’t an efficient or accurate way to provide good acoustical conditions. Marks says, “Even when all separating partitions are rated to STC 50, a suite’s occupants can still experience annoying noise from neighbouring suites and adjacent hallways.”
Often, these disturbances are a result of flanking noise.
The advantage of testing for ASTC is that it takes a holistic acoustical approach, one that accounts for direct transmission and flanking noise. Instead of checking that partitions meet a specific STC rating, ASTC is determined by calculating the combined effect of each sound transmission path, airborne and flanking, between dwellings.
What’s more is that architects and developers are now required to demonstrate compliance. So instead of just verifying that each separating wall, floor, and ceiling meets an STC rating of 50, you have to show that separating assemblies meet the ASTC criterion of 47, which better reflects a building’s overall acoustical environment.
Demonstrating Compliance with Your Friendly, Neighbourhood Acoustician
To meet the code’s new acoustical requirements, Marks recommends taking one of three approaches:
- using established partition designs that have already undergone extensive testing and meet the code’s acoustical criteria;
- conducting post-construction acoustical testing of as-built separating assemblies; or
- designing new separating assemblies with the help of a suitably qualified acoustician.
For the first approach, select assemblies that have a minimum STC rating of 50, as measured in accordance with ASTM standards or conforming to the Fire and Sound Resistance tables presented in the BC building code. Then an acoustical consultant can review your building plans to confirm that separating partitions meet the new requirements for flanking noise and, if necessary, make recommendations to upgrade wall, ceiling, and floor assemblies.
The second option is to conduct field measurements to check that ASTC is at least 47. These measurements need to be performed according to ASTM standards by a qualified acoustician, who would provide results and recommendations in a detailed report.
The third approach is to work alongside an acoustician during the design phases to ensure partitions rate to ASTC 47, as determined by the methods presented in the code.
By working with BKL early on, you can take advantage of our specialized knowledge and experience, and design the acoustics from the top down, an approach that’s much more efficient than simply reviewing floorplans and making recommendations to address trouble spots. Using laboratory data and digital 3-D models, our acousticians can provide accurate ASTC predictions based on analysis of standard and non-standard assemblies, as well as insulating materials.
Alternately, you could calculate the ASTC rating using readily available tools and resources.
Marks suggests using soundPATHS, a free online app developed by the National Research Council, to estimate ASTC ratings for common assemblies. Or you can look through the council’s “Guide to Calculating Airborne Sound Transmission in Buildings.” It shows how various wall and floor/ceiling constructions conform to ASTC ratings. In these situations, an acoustician can guide you through the process and help you calculate ASTC.
By incorporating acoustical criteria that more accurately reflect real-world conditions, BC’s updated building code encourages better building acoustics. When applied correctly, these requirements will result in higher-quality living conditions in multi-family residential units across the province, helping more people enjoy peace and quiet in the comfort of their homes.
Download this handy guide for a summary of the updates and how we can help you comply with the new acoustical requirements in the 2018 BC Building Code.