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13 November 2017

Acoustical plenum barriers meet occupant expectations and comply with standards - part 3

How do I implement plenum barriers in my designs?

Author: Gary Madaras, PhD, Assoc. AIA, Rockfon Acoustics Specialist for North America

This is the third article in a three-part series on using acoustical plenum barriers for sound privacy. The first article described what plenum barriers are and why you need them on projects going forward. The second article explained why you can't use suspended acoustical ceilings to block sound and should consider the cost impact of using full-height walls.

After reading the previous articles, we hope that you’re saying, “Okay, I'm convinced.” Here are a few more answers to help use plenum barriers to meet occupants’ expectations and comply with acoustic standards.

How do I implement plenum barriers in my designs?

The first step is to determine the sound-blocking capacity of the partition below the ceiling. If you're following the recommendations of an acoustics consultant or you’re complying with the requirements of an acoustic standard, guideline or building rating system, then the rating of the partition is most likely STC 40, 45 or 50. Also, remember to consider any doors or windows that penetrate the partition, which typically will drop the composite sound-blocking capacity. The partition shared with the corridor may have a lower composite rating than those common to other enclosed rooms that do not have doors or windows.

If the partition is rated STC 35 to 40, a single-layer plenum barrier of 1.5-inch-thick stone wool with a fiber-reinforced, foil facing on one side should be used above the ceiling level. When combined with a suspended, stone wool, acoustic ceiling, a single-layer plenum barrier tests at STC 40. A single-layer plenum barrier typically is used over the partition with the door(s) leading into the room, which is usually the weak link in the overall room enclosure.

If the partition is rated STC 45 to 50, a double-layer plenum barrier is used above the ceiling. The same 1.5-inch-thick, foil-faced, stone wool boards described for single-layer plenum barriers are used. The two layers are separated by airspace of 1 to 2 inches in width to optimize performance. When combined with a suspended, stone wool, acoustic ceiling, a double-layer plenum barrier tests at STC 52. A double-layer plenum barrier typically is used over partitions between enclosed rooms that have no doors or windows.

If the partition is not rated, or is rated STC 30 or lower, do not use plenum barriers. The partition is insufficient to provide sound or speech privacy and using a plenum barrier above the ceiling provides no acoustical benefit. If the partition is STC 55 or higher, then it should extend full height above the ceiling to the structural floor or roof above and should be sealed airtight.

Is it really that simple? There must be more to it.

Stone wool plenum barriers are as simple as they sound, but here are few details to help optimize their value and performance

They are held in place using a combination of mechanical fastening at the top (two self-tapping metal screws and insulation washers into a standard metal channel), taping along the sides and a friction-fit along the bottom. The installing contractor cuts the boards slightly larger than the space they are filling. As the barriers are installed, they are compressed vertically and laterally. The friction along the top of the partition and the underside of the deck above can hold the barrier in place. The contractor then uses butt-joint tape over the vertical seams between adjacent boards. No seals, gaskets or caulking generally is required. Additional installation details are available at www.OptimizedAcoustics.com.

The drawings for new construction should indicate that ducts, conduits and pipes associated with the building's mechanical, electrical, plumbing and fire suppression systems should not run over rooms with plenum barriers. There is usually plenty of room to run these utilities down the corridor or over open areas. The only penetrations through the plenum barriers should be for the utilities serving that particular room: the supply duct, the return air opening or duct, and perhaps a pipe associated with the fire suppression system. These penetrations should be located over the door into the room. Unless the door is STC-rated with a heavy panel and full perimeter gaskets, it will be the weak link in the room envelop. Locating the plenum barrier penetrations over the door results in no further degradation in sound isolation than is already present from the door.

Plenum barriers are commonplace in Canada and some European countries, and are required in some of their acoustics standards. Plenum barriers are becoming more recognized and utilized in the United States. Their required use is appearing in U.S. standards, guidelines and building rating systems. This three-part introduction to plenum barriers can help their effective implementation into projects in the future.

If you have questions about how to effectively use plenum barriers and ceiling systems for optimized acoustics, please visit www.OptimizedAcoustics.com follow us on LinkedIn, or call us at 800-323-7164, email cs@rockfon.com or click here to find a representative in your area.


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