Sound Control ASTC Solutions in the 2015 NBCC for Wood Buildings

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The 2015 edition of the National Building Code of Canada (NBCC) introduced 360 technical revisions including requirements for better sound control.

Parts 3 & 9 of NBCC 2015 raises the bar for sound control with the introduction of the apparent sound transmission class (ASTC) rating.  This gives a more comprehensive description of noise between dwellings—with the inclusion of sound transmitted through flanking paths —than the longstanding sound transmission class (STC) rating. This is particularly important as there are many more paths with wood frame construction. Fortunately gypsum can be used for both sound control and fire protection. The 2015 NBCC for low-rise, mid-rise and high-rise residential buildings now provides for a minimum ASTC rating of ≥47 for wall/floor assemblies.

Developed as a smarter alternative to more common sound control methods on interior walls and ceilings, the SilentFX® QuickCut™ Acoustic System is a single-panel gypsum board product that contains a viscoelastic polymer core applied between two specifically formulated thin layers of gypsum board. The polymer core acts as a shock absorber that dampens board vibrations and dissipates the sound energy into thermal energy.  This product is available in 12.7mm or 15.9mm thickness the same as traditional gypsum board thicknesses and is ideal for new construction or renovations over both wood and steel framing.

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(NRC sketch showing single or triple staggered wood stud walls with 1 layer of 15.9mm (5/8” SilentFX QC gypsum board directly attached and 89mm sustainable insulation.)

Replacing traditional multi-layered gypsum systems with one laminated noise-reducing gypsum board on one side of the partition, allows contractors to build effective noise-reducing wall assemblies. An example of this, using less materials and no special tools, is a National Research Council of Canada (NRC) third party tested rating of ASTC 48 (See NRC sketch).  Use of this acoustical gypsum board cuts construction time and material and labour costs, and helps the project gain valuable floor space. The minimal amount of material required also contributes to sustainability and contributes to better green building acoustics.

When working with laminated noise-reducing gypsum board, installers may follow traditional interior gypsum board application and finishing methods and should apply attention to details for acoustic performance. For instance, the board layout should stagger joints from one side of the wall to the other. Next, sound-absorbent fibreglass batt insulation should be installed in wall cavities, for higher ASTC ratings. Resilient channels are not necessary to achieve performance in this application.  In fact, if installed incorrectly, the resilient channel act as short circuits for sound.

To achieve the sound ratings provided in Code tables and National Research Council (NRC) tests, acoustical sealant is required at electrical boxes and at junctions of intersecting walls and floors

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Conclusion

Wood-framed mid-rise residential construction costs less than poured concrete for mid-rise buildings according to a recent report from the Building Industry and Land Development Association (BILD). They estimate the use of wood framing compared to poured concrete can save project teams $300 to $400/m² ($30 to $40/sf). Applying innovative sound control ASTC solutions that meet and exceed the requirements of the NBCC will help design and construction professionals create more affordable living spaces and enhance the wellbeing of occupants.

For more information please visit; http://www.kenilworth.com/publications/cc/de/201612/?page=18 and for more Building Knowledge for your project, please contact the writer or our regional architectural solutions managers or call our toll free Professional Line 800-233-8990.

Bob Marshall is the Building Science Manager for CertainTeed Gypsum Canada and can be reached at robert.marshall@saint-gobain.com. He has been appointed by NRC to the Standing Committee on Energy Efficiency in Buildings.

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Bob Marshall is Building Science Manager for CertainTeed Gypsum Canada

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