Decibels and Dwellings: Noise Control Evolution in the NBC

by tanya_martins_2 | May 17, 2024 9:41 am

By Todd Busch

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The evolution of soundproofing standards within the National Building Code of Canada (NBC) offers a fascinating journey through nearly eight decades of architectural and acoustic advancements. Beginning in 1941 with a modest requirement of a 45 dB sound transmission loss between dwelling units, the code has undergone a series of revisions and enhancements, reflecting both technological progress and societal needs.

From the initial focus on basic sound attenuation to the incorporation of more sophisticated metrics such as the Sound Transmission Class (STC) ratings, and later, the Apparent STC (ASTC) measurements, each iteration has aimed to address emerging challenges in noise control and ensure enhanced living environments for occupants. This article traces the key milestones in the evolution of soundproofing regulations within the NBC, highlighting significant amendments, pivotal additions, and the ongoing considerations for future updates in response to evolving building practices and acoustic standards.

1941

Starting in 1941, the NBC required walls and floors between dwellings to be sound transmission loss of
45 dB or higher and transmission loss (TL) was defined. There were no standardized testing procedures referenced at that time. There were prohibitions on the attachment of fixtures to walls separating dwelling units including plumbing, water-supply pipe, drainage pipe, or mechanical equipment. Refuse chute construction was described by specifying a minimum 0.9 kg/m² (2.156 lb/ft²) (18 gauge) surface weight.

1954

In 1954, references to compromising air leaks were introduced. Specifically, “The required sound insulation can not be obtained if air leaks exist in any layer of the intervening construction.” The 45 dB rating requirement between dwelling units was retained unchanged.

1965

In 1965, STC 45 performance was added for a variety of service rooms to the effect that, “Every service room or space such as storage room, laundry, workshop or building maintenance room and garages … when not located in a dwelling unit, shall be separated from the dwelling units by a construction providing … [an STC rating of 45 or greater].” ASTM E90-61T, Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, was introduced as an acceptable methodology for measuring the TL and obtaining STC ratings.

The laboratory STC rating is determined using a curve-fitting procedure using TL data for the 125 Hz through 4,000 Hz, one-third-octave bands. Given the limited frequency range, there can be certain sound sources that generate greater amounts of sound energy at lower frequencies. These include musical instruments and mechanical equipment. Plumbing and piping introduces a problematic sound source due to the passage of these objects through equipment chases and other wall cavities. Noise from such sources may not be adequately controlled due to the omission of low-frequency energy content. The STC is typically applied to partitions but can be extended to include floor-ceiling assemblies in circumstances where sound transmission issues arise between vertically stacked units.

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1970s

In 1970, a table was added for the first time showing “sound ratings” of acceptable assemblies, classified as either I or II, and distinct from the stipulated STC 45 rating between dwellings. ASTM E90-66T was introduced.

Minor changes occurred in the 1975 edition. ASTM E90-70 was introduced.

Minor changes also occurred in the 1977 edition. ASTM E90-75 was introduced.

1980

More change occurred in the 1980 edition. Now in addition to STC 45 between dwellings, “Where a dwelling unit is adjacent to an elevator shaft or a refuse chute, the separating construction shall have [an STC] rating of at least 50 or shall have a “sound rating” of I or II as described [in the accompanying table].” ASTM E90-75 was retained and ASTM E336-77, Standard Test Method for Measurement of Airborne Sound Attenuation between Rooms in Buildings, was introduced. The table of acceptable assemblies had no fewer than 28 fire and “sound ratings” indicated for various wall constructions and no fewer than eleven for floors, ceilings, and roofs.

1985

Minor changes occurred in the 1985 edition. Newly introduced language stated, “Building services located in an assembly required to have [an STC] rating shall be installed in a manner that will not decrease the required rating of the assembly.” ASTM E90 and ASTM E336 were now referenced to their most-recent editions in different sections of the NBC.

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1990

In 1990, the increased performance of STC 50 between dwellings was introduced for separations between dwelling units along with an STC 55 provision for elevator shafts and refuse chutes. ASTM E413, Classification for Rating Sound Insulation, was introduced to accompany ASTM E90 and ASTM E336. More performance specificity was added by stipulating compliance with measurements that were conducted in terms of the relevant ASTM standards or as could be found in the table of fire and STC ratings. The so-called “sound ratings” were dropped.

1995

No significant changes occurred for the 1995 edition, although reference was now clearly made to ASTM E492-90, Standard Test Method for Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine, and ASTM E1007-97, Standard Test Method for Field Measurement of Tapping Machine Impact Sound Transmission Through Floor-Ceiling Assemblies and Associated Support Structures, as they pertain to impact insulation class (IIC) testing, which was heretofore not included. The NBC for 1995 was apparently published on a backdated basis as it contains reference to standards published in later years. The IIC can be of importance when dealing with a selection of sound sources including people walking in high heels or other hard-soled shoes and play involving bouncing balls and jumping.

Despite references to these standards, neither design nor performance testing for IIC was required in this edition of the NBC. The overall number of tabulated assemblies for walls along with floors, ceilings, and roofs was greatly increased from prior editions of the NBC and the associated information modified to include fire-resistance ratings, STC ratings, and IIC performance ratings.

2005, 2010

No significant changes occurred for the 2005 NBC edition.

The 2010 edition saw language added for secondary suites where either an STC 43 rating was stipulated or specific construction utilized, to the effect that “Where a house contains a secondary suite, each dwelling unit shall be separated from every other space in the house in which noise may be transmitted by construction:

1. whose joist spaces are filled with sound-absorbing material of not less than 150 mm nominal thickness,
2. whose stud spaces are filled with sound-absorbing material,
3. having a resilient channel on one side spaced 400 or 600 mm o.c., and
4. having 12.7 mm thick gypsum board on ceilings and on both sides of walls.”

 

2015, 2020

The 2015 edition added in the option of demonstrating either an ASTC performance of 47 or laboratory tested STC 50 for dwellings (or greater when sound flanking paths is also considered). It was noted, “An ASTC measurement or calculation will always yield a value equal to or lower than the STC for the same configuration, as the ASTC includes sound flanking transmission.” The National Research Council of Canada (NRC) software, soundPATHS, was referenced as an acceptable tool for analyzing future performance when flanking is considered as required. Flanking paths contribute to deviations between the ASTC and the laboratory STC since they bypass the partition element that was subject to controlled testing. Additional reference was made to ISO standards regarding flanking paths, including ISO 15712-1, Building acoustics—Estimation of acoustic performance of buildings from the performance of elements—Part 1: Airborne sound insulation between rooms, and ISO 10848 which is comprised of five separate standards. Supplemental tabulations were incorporated providing, “Options for Design and Construction of Junctions and Flanking Surfaces to Address Horizontal and/or Vertical Sound Transmission Paths.” Further, limitations on sound ratings of fans in terms of “sones” was incorporated through reference to CAN/CSA-C260-M, Rating the Performance of Residential Mechanical Ventilating Equipment, and HVI publication 915, “Loudness Rating and Testing Procedure.”

No significant changes occurred for the 2020 NBC edition.

Discussion

The Canadian Board for Harmonized Construction Codes (CBHCC) is the organization reviewing further changes to the NBC. Currently, there are several topics of interest. Future changes are being considered for IIC, in terms of making performance testing mandatory, for making controls over the construction of exterior facades a topic that would allow for greater control of exterior noise intrusion, and other methods of design and construction that would limit problematic experiences of dwelling residents—due to the low-frequency sources that are typically found within service rooms such as mechanical rooms. An additional possibility involves the extension of the STC provisions to both educational and health-care facilities nationwide, which would greatly expand the scope of application of the acoustical provisions of the NBC to a wider range of buildings.

Conclusion

The progression of the NBC, from 1941 through to the most recently adopted edition in 2020, contains a progression of the acoustical requirements for residential dwellings. From the earliest point in time, a minimum of sound transmission performance was stipulated to limit intrusive noise between dwellings. Further investigation is underway to determine if further additions and refinements of the NBC are favoured which could occur within the next publication expected in the year 2025.

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Author’s note

The author would like to thank Morched Zeghal of Codes Canada for sharing the historical information about the past editions of the NBC that are the basis for this paper, and for ongoing co-ordination of CBHCC activity pertaining to the NBC 2025 code cycle.

The impact insulation class (IIC) can be of importance when dealing with a selection of sound sources including people walking in high heels or other hard-soled shoes and play involving bouncing balls and jumping.

Starting in 1941, the National Building Code of Canada (NBC) required a sound transmission loss between dwelling units of 45 dB or higher.

Future changes are being considered for impact insulation class (IIC), exterior noise control, and low-frequency sources.

Source URL: https://www.constructioncanada.net/decibels-and-dwellings-noise-control-evolution-in-the-nbc/

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