340B

Index of Sections


SECTION 340B - SOUND TRANSMISSION CONTROL
Code Plain English

340B.1 General.

Individual JLWQ shall comply with Division IIA of Appendix Chapter 12A as for apartment houses and as provided in this division. Existing buildings being converted to F-7 JLWQ Occupancies are not required to, but, are recommended to consider exterior noise sources pursuant to Section 1208A.8.4.

340B.1 General.

In general there are three types of sound issues in buildings.

  1. Sound transmission in general between spaces, such as speech, usic, etc..
  2. Impact transmission such as the sound of high heels on a floor s heard below, and
  3. Exterior noise such as traffc, trains and the general din of he environment, which can be measured.

Sound Transmission Class (STC) is a numerical designation given tested walls and floor/ceiling assemblies which express the number of decibels by which the assembly will reduce sound levels as perceived from one side of the assembly to the other. STC 50 is the minimum level which must be achieved between all live/work units and between the units and any corridor or interior common spaces. A typical wood stud wall achieving STC might have two layers of 5/8" sheet rock on one side and one layer of the same mounted on resilient channels, a sort of sheet-metal sound-absorbing leaf springs, which are in turn affxed to studs. The whole thing gets insulated, caulked around the edge, and inspected.

Sound impact (IIC) also is required to meet or exceed a rating of 50. It should be noted that in a building with concrete floor/ceilings, an 8" thick slab will usually not meet IIC 50 without the addition of carpet or an acoustic mat under a topping slab or heavy wood floors.

Live/work units must consider and respond to "exterior noise sources". These can be measured with testing equipment and are usually expressed as "CNEL," which means "Community Noise Level". Once measured, in live/work a means must be devised to reduce the CNELlevel down to 45 decibels (dB s). If CNEL is presently 65, then a wall assembly must be devised which cuts the level by 20 decibels, i.e. have an STC rating of 20 or greater. Standard double-glazed windows will achieve a rating of STC 28, for example.

The live/work code clearly states that in the renovation of existing buildings, alterations are recommended but not required to comply with requirements regarding outside noise sources except in the case of alteration of the exterior walls or floor/ceiling assemblies of the building. As an example, a warehouse conversion to live/work that did not replace exterior single-glazed industrial sash windows would be exempt. If the windows were being replaced, they would be required to have an STC rating that would be capable of reducing measured CNEL to 45.

340B.1.1 Notice of limitation.

A "notice of limitation" pursuant to Section 325B.5 shall be provided for all F-7 Occupancies where individual JLWQ are abutting other habitable spaces.

  

340B.2 Airborne Sound Insulation.

340B.2.1 General.

Buildings or a portion of buildings classified as F-7 Occupancies shall comply with Division IIA of Appendix Chapter 12A as for apartment houses by providing STC 50 walls and floor/ceilings where a designated residential area abuts another occupied or public area and as provided in this division.

  

340B.2.2 Commercially/ Industrially-oriented JLWQ as noise source.

Any individual F-7 JLWQ space that is a source of noise above 60db such as a rock band practice shall add construction elements that provide an additional 50 STC to the existing walls and floor/ceiling that abuts adjacent residential occupancies or public area serving a residential occupancy. Alternatively, the space may comply with the recommendations of an acoustic analysis

340B.2.2 Commercially/ Industrially-oriented JLWQ as noise source.

Sources of sound in work/live units are sometimes different that those in typical residences. Certain work uses such as amplified music production (rock bands, etc.) or other mechanical devices such as grinders or shop tools may generate in excess of 60 decibels. In such cases (and they may come up after the conversion is complete, based on the unit occupant’s activities), there are two choices:

  1. Add an additional 50 STC to the walls and an additional 50 IIC o the floor/ceiling which separates the higher noise source from ny other units’ residential portions. This might be accomplished y creating a second demising wall a few inches from the one that ould normally be required and which itself is rated at 50 STC. he result would be an STC somewhere around 100, almost what one ould call "sound proof".
  2. Hire an acoustical engineer to show that the assemblies being roposed will result in an acceptable noise level in occupied paces outsides the noise source in questions. Though this may eem like an expensive way to go,

    • An acoustical engineer is probably needed anyway to determine that the noise source in excess of 60 db exists, and
    • Rather than adding entirely new 50 STC/IIC assemblies (the "default" method), he or she may recommend a far more economical alternative.

340B.3 Impact Insulation.

340B.3.1 General.

Buildings or a portion of buildings with individual spaces or JLWQ shall comply with Division IIA of Appendix Chapter 12A as for apartment houses by providing IIC 50 floor/ceilings where a designated residential area abuts another occupied or public area and as provided in this division.

  

340B.3.2 Commercially/ Industrially-oriented JLWQ as noise source.

Any individual F-7 JLWQ space that is a source of impact noise above 60db shall add construction elements to separate the source of impact noise or provide an additional IIC 50 to the floor/ceiling that abuts adjacent residential occupancies or public area serving a residential occupancy. Alternatively, the space may comply with the recommendations of an acoustic analysis.

  

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