Building & construction design considerations
In the previous blog we covered “sound”, what it is & the principles of panel design and manufacture so as to minimize the transference of sound “through” an installed partition.
Not all sound transference occurs “through” the partition. “Flanking noise” is sound reaching an adjacent room (the other side of the partition) by an indirect path or as commonly called a “flanking path”. “Direct noise” is sound reaching an adjacent room through the partition panel. Panel construction along with proper installation is responsible for minimizing “direct noise” Building construction is responsible for eliminating “flanking paths” and therefore minimizing “flanking noise”.
Building Construction Issues.
- Install a sound baffle complete & continuous without any penetrations (no ductwork) from finished ceiling to underside of building structure. Preferably a double thickness of ½” gypsum board with staggered joints. Void shall be filled with acoustic insulation. Completed baffle shall have a proven and tested STC equal or greater than the partition. Baffle must be installed during building construction rather than after partition is installed. Ensure that access to the track for future leveling purposes is provided
- The permanent walls at each end of the operable partition should be solidly blocked to the building structure behind the wall finish. The partition should not seal to a hollow wall as sound will travel around it.
- Ductwork should not penetrate the sound baffles above partition. The void above operable partition should not function as an air plenum. If ductwork must penetrate the baffle then sound-attenuating duct or duct silencers shall be used.
- All storage pockets should have the same flooring as under the partition in order to eliminate any gaps resulting from partitions sealed against different or unequal floor thicknesses.
- If a hollow floor system is used then a barrier should be installed directly under the partition.
- Floor and track must be level. Floor shall not vary from a smooth level surface by more than +/- 1/8” in 12’. Track shall be installed level & true.
- If partition seals on carpet then in these areas and extending a minimum of 4” on either side a metal strip should be installed to provide a flat surface.
- Where the partition seals against permanent walls using expandable panels, bulb seals, fixed or recessed jambs then an airtight smooth surface should be provided with all gaps caulked with clear acoustic caulking. Building features such as baseboards & crown moldings shall be notched or modified to eliminate uneven surfaces. Interfaces between track and ceiling shall be caulked
- Flanking paths that are most common are duct work, electrical wiring, pipes for sprinklers or water, natural gas piping, access flooring, carpeted or uneven floors. All must be caulked or otherwise sealed to minimize sound transfer.
- A minimum STC 50 to 55 partition should be used in order to attain any degree of acoustic privacy. Ensure that the sound test is recent (no more than ten years old) and conducted as per currently acceptable ASTM standards in an independently approved acoustical laboratory (NVLAP).
- Check the description of the tested (published STC) partition specimen ensuring that what was tested matches what is being supplied. For example a sound test may indicate the use an expandable closure but the proposed partition may be based on a hinged closure: not the same and may not result in expected acoustic performance. In particular verify that the panel specimen tested was in the generally accepted 9’ X 14’ opening, 3 panels plus closure panel minimum and maximum panel width of 48”. If the test was conducted in a smaller test opening with wider panels (fewer joints between panels are tested) then the resulting STC test numbers are suspect
- Partitions should close against permanent walls and not to the face of pocket doors. Pocket doors are typically not as good acoustically.
- Lay out partitions so as to eliminate or minimize the use of pass doors or other penetrations. Do not use windows or other features that require openings in the partition. Minimize the use of “flush mounted” accessories such as writing surfaces and tack boards. Surface mount these items. When you “break” the tested surface of a partition a path (a hole) for “direct” noise through that panel is created.
- Base seals (preferably mechanically operated rather than automatic) should seal against a hard smooth surface and not carpet or other non flat floor coverings. Carpet fibers are a major flanking path and sound will travel through them and under the partition.
- Maximum base seal travel should be 2”. Mechanically activated seals are preferable over automatic as they exert a measurable & predictable pressure and therefore are better acoustically. Seal travel more than 2” requires a larger cavity in the panel base and a resulting acoustical leak due to the void.
- Track systems that have an integral (built in) soffit are preferable. To be equal those that have a removable soffit would require to be caulked to the track to obtain an equivalent acoustic level.
- Avoid having in the room track intersections that are running perpendicular to the partition. The void in the track will freely allow the transference of sound where the partition crosses.
- An expandable final closure is preferable to all others and mandatory if it was the closure used in the laboratory test.
Finally ASTM E-557 is titled “Standard Guide for The Installation of Operable Partitions” but what it is in addition is a guide as to how to minimize “flanking paths”. I would encourage all to read it. Contact Moderco to get all details at info@Moderco.com
To be continued.