SynC™

SynC · SynC Standards

Acoustic Insulation

Rev8
IssuedSep 14, 2026
Contents

Revision history

Download
Build a datasheet from this standard Start a project with this standard already attached — one click, no setup.
Use in a project

1 Scope

NOTE This standard governs the selection, fire and smoke properties, density, thickness, retention, installation, and verification of sound-attenuation insulation placed inside interior partition cavities, inside floor-ceiling assemblies, and above suspended ceilings for the purpose of reducing airborne sound transmission between spaces. (1.1)
NOTE The fill covered here is one component of a tested assembly. The sound transmission class of a partition or a floor-ceiling assembly is a property of the whole system, in which the board layers, the framing and its spacing, the cavity depth, the decoupling accessories, the perimeter seal, and the cavity fill each contribute, and the tested assembly that a project cites fixes all of them together. (1.2)
NOTE Cavity fill raises transmission loss by damping the air in the cavity rather than by adding mass. Air oscillating through a porous fiber matrix loses energy to friction, which suppresses the mass-air-mass resonance of a double-leaf partition and absorbs the standing waves that would otherwise couple the two faces through the cavity. (1.3)
NOTE Because the fill works by airflow resistance and not by weight, its contribution rises steeply from an empty cavity to a lightly filled one and then flattens; beyond the density at which the flow resistance of the fill exceeds what the cavity needs, added density buys stiffness and fire performance rather than sound transmission class. (1.4)
NOTE The following are governed elsewhere and are outside this standard: (1.5)
  • the gypsum board partition, its framing, resilient channels, multi-layer board schedules, perimeter acoustic sealant, and the offset and treatment of electrical boxes, which are governed by Gypsum Board AssembliesGypsum Board AssembliesResolves to the current adopted revision.sync/gypsum-board-assemblies
  • thermal insulation in the building envelope, including any vapor retarder the envelope needs, which is governed by Building Thermal InsulationBuilding Thermal InsulationResolves to the current adopted revision.sync/building-thermal-insulation
  • firestopping of penetrations and of the head-of-wall joint in fire-resistance-rated assemblies, which is governed by FirestoppingFirestoppingResolves to the current adopted revision.sync/firestopping
  • the ceiling attenuation class of a suspended ceiling system, which is governed by Suspended Acoustical CeilingsSuspended Acoustical CeilingsResolves to the current adopted revision.sync/suspended-acoustical-ceilings
  • exposed sound-absorbing wall and ceiling finishes, which are governed by Acoustic Wall PanelsAcoustic Wall and Ceiling PanelsResolves to the current adopted revision.sync/acoustic-wall-panels and Acoustic Ceiling Clouds And BafflesAcoustic Ceiling Clouds and BafflesResolves to the current adopted revision.sync/acoustic-ceiling-clouds-and-baffles
  • acoustic seals at door and frame perimeters, which are governed by Doors Frames And HardwareDoors, Frames, and HardwareResolves to the current adopted revision.sync/doors-frames-and-hardware
  • duct liner, duct wrap, and pipe insulation, which are governed by HVAC DuctworkHVAC DuctworkResolves to the current adopted revision.sync/hvac-ductwork and Mechanical InsulationMechanical InsulationResolves to the current adopted revision.sync/mechanical-insulation
  • the wood or cold-formed steel framing that forms the cavities, which is governed by Wood FramingWood Light FramingResolves to the current adopted revision.sync/wood-framing and Cold Formed Metal FramingCold-Formed Metal FramingResolves to the current adopted revision.sync/cold-formed-metal-framing
1.6 The partition types that receive acoustic cavity fill shall be as indicated on the partition schedule.
1.7 The floor-ceiling assemblies that receive acoustic cavity fill shall be as indicated on the floor and ceiling assembly schedule.
1.8 Where one product serves both the acoustic function under this standard and the thermal function of the building envelope, the thermal resistance, vapor retarder, and air barrier requirements of Building Thermal InsulationBuilding Thermal InsulationResolves to the current adopted revision.sync/building-thermal-insulation shall govern the product, and this standard shall govern its acoustic density, thickness, fit, and retention.
1.9 The Contractor shall coordinate the cavity fill with the partition work under Gypsum Board AssembliesGypsum Board AssembliesResolves to the current adopted revision.sync/gypsum-board-assemblies, so that the fill, the framing, the board layers, and the perimeter seal are the components the cited tested assembly requires.

2 Referenced Standards

2.1 Materials, testing, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited in the Contract Documents.
2.2 Where the contract documents, the adopted building code, or a referenced standard impose conflicting requirements, the more stringent requirement shall govern unless the Architect of Record directs otherwise in writing.
Standard Title
ASTM C665 Mineral-Fiber Blanket Thermal Insulation for Light Frame Construction and Manufactured Housing
ASTM C553 Mineral Fiber Blanket Thermal Insulation for Commercial and Industrial Applications
ASTM C612 Mineral Fiber Block and Board Thermal Insulation
ASTM C1320 Installation of Mineral Fiber Batt and Blanket Thermal Insulation for Light Frame Construction
ASTM C522 Airflow Resistance of Acoustical Materials
ASTM C518 Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
ASTM C1338 Determining Fungi Resistance of Insulation Materials and Facings
ASTM E84 Surface Burning Characteristics of Building Materials
UL 723 Surface Burning Characteristics of Building Materials
ASTM E136 Behavior of Materials in a Vertical Tube Furnace at 750°C
ASTM E119 Fire Tests of Building Construction and Materials
UL 263 Fire Tests of Building Construction and Materials
ASTM E90 Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements
ASTM E413 Classification for Rating Sound Insulation
ASTM E336 Measurement of Airborne Sound Attenuation Between Rooms in Buildings
ASTM E1414 Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum
ASTM E492 Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine
ASTM E989 Classification for Determination of Impact Insulation Class
ASTM E1007 Field Measurement of Tapping-Machine Impact Sound Transmission Through Floor-Ceiling Assemblies and Associated Support Structures
ASTM E96 Water Vapor Transmission of Materials
GA-600 Fire Resistance and Sound Control Design Manual
UL Fire Resistance Directory Fire-Resistance-Rated Systems and Products
ICC IBC International Building Code
ICC IMC International Mechanical Code
NFPA 90A Installation of Air-Conditioning and Ventilating Systems

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for review before acoustic insulation is procured:
  • product data for each product, stating the fiber family, the product form, the product standard and type designation, the nominal density, the thicknesses and widths furnished, the facing if any, and the airflow resistance per ASTM C522 where the manufacturer publishes it
  • surface burning test reports per ASTM E84 or UL 723 for each product, and for the faced product as installed where a facing is furnished
  • noncombustibility test reports per ASTM E136 for each product required to be noncombustible
  • fungi resistance test reports per ASTM C1338 where the datasheet requires them
  • a schedule listing every partition type and floor-ceiling assembly that receives fill, the tested assembly cited for it, and the product, density, and thickness proposed for it
  • laboratory test reports per ASTM E90, ASTM E492, or ASTM E1414 supporting each cited tested assembly that is not a published design
  • manufacturer's installation instructions, including the batt widths designated for each framing spacing and framing material, and the published limits on cavity height without supplemental retention
  • product data for retention devices, support wires, netting, impaling pins, and adhesives
  • a sample of each product, not less than 12 in. by 12 in., in the thickness and density proposed
Action Submittals Requiredcheckbox
☑ Product data for each acoustic insulation product
☑ Surface burning test reports per ASTM E84 or UL 723
☐ Noncombustibility test reports per ASTM E136
☐ Fungi resistance test reports per ASTM C1338
☑ Schedule of assemblies, tested assembly citations, and proposed products
☐ Laboratory acoustic test reports supporting cited assemblies
☑ Manufacturer's installation instructions
☐ Retention device and adhesive product data
☐ Product samples
3.1.2 Acoustic insulation shall not be installed in any assembly until the submittals covering the products in that assembly have been reviewed and returned.
3.1.3 The Contractor shall submit a written request before procuring any product that differs in fiber family, density, thickness, or facing from the reviewed submittal, and the request shall identify each tested assembly the change affects.

3.2 Closeout Submittals

3.2.1 The Contractor shall submit the following before the assemblies containing acoustic insulation are accepted:
  • a signed certificate stating that the installed insulation conforms to the reviewed submittals, the cited tested assemblies, the manufacturer's published instructions, and this standard
  • inspection records for each area inspected before concealment, identifying the date, the inspecting party, the assemblies inspected, and the disposition of any deficiency
  • field acoustic test reports where field testing is required
  • mock-up review records where mock-ups are required
  • manufacturer warranty documents for each product that carries a written material warranty
Closeout Submittals Requiredcheckbox
☑ Signed certificate of conformance
☑ Inspection records before concealment
☐ Field acoustic test reports
☐ Mock-up review records
☐ Manufacturer warranty documents

4 Quality Assurance

4.1 Installer Qualifications

4.1.1 Acoustic insulation shall be installed by personnel experienced in cavity insulation for commercial partition and floor-ceiling construction.
4.1.2 The installing foreman shall have installed cavity fill in acoustically rated or fire-resistance-rated assemblies on not fewer than three completed projects.
NOTE Cavity fill is concealed within days of installation and its shortcomings surface months later as a room that fails a field test or a tenant complaint, so the skill that matters is the discipline of splitting, fitting, and filling around every obstruction rather than any special tooling. (4.1.3)

4.2 Preinstallation Coordination

4.2.1 Before the first cavity is filled, the Contractor shall confirm against the reviewed schedule that the product, density, and thickness on hand for each partition type and floor-ceiling assembly match the tested assembly cited for it.
4.2.2 The Contractor shall coordinate the sequence of cavity fill with the framing, electrical, plumbing, fire protection, and low-voltage trades so that in-cavity rough-in is complete before the fill is placed.
4.2.3 Where a trade must reopen a filled cavity, the Contractor shall reinstate the fill to its inspected condition before the cavity is closed.

4.3 Inspection Before Concealment

4.3.1 The assemblies whose cavity fill is inspected before the closing face is applied shall be as indicated in the datasheet.
Cavity Fill Inspection Before Concealmentselect
Every cavity that receives fill
Fire-resistance-rated and acoustically rated assemblies
Fire-resistance-rated assemblies
A representative sample of each partition type
None beyond the inspections the adopted code requires
4.3.2 The Contractor shall give the inspecting party not less than two working days' notice before the closing face of an assembly selected for inspection is applied.
4.3.3 The Contractor shall not apply the closing face of an assembly selected for inspection until the fill has been inspected and released, or until the inspecting party has waived the inspection in writing.
4.3.4 Where the parties disagree whether a cavity is completely filled, the Architect of Record shall make the initial determination.
4.3.5 A cavity that is closed without a required inspection shall be reopened at the Contractor's expense to the extent the inspecting party requires to verify the fill.

4.4 Product Labeling

4.4.1 Each product shall be labeled by the manufacturer with the product name, the fiber family, the product standard and type designation, the nominal density, the thickness, and the surface burning classification.
4.4.2 Labels shall remain on delivered bundles until the bundle is opened at its point of installation.
4.4.3 Insulation that cannot be identified to a reviewed submittal shall be removed from the site.

4.5 Fungi Resistance

NOTE Mineral fiber and glass fiber are inorganic and do not themselves feed fungal growth, but dust, organic debris, and the organic binder on the fiber surface can support growth where the fill stays wet, so a dry cavity is the primary defense and the test evidence is a secondary one. (4.5.1)
4.5.2 The evidence of fungi resistance furnished for each product shall be as indicated in the datasheet.
Fungi Resistance Evidenceradio
○ ASTM C1338 test report showing no growth
○ Manufacturer's written statement of inorganic composition
○ Not required

5 Environmental and Service Conditions

NOTE Acoustic cavity fill under this standard is intended for dry, conditioned interior cavities and plenums, and the products it covers are not selected for repeated wetting, condensation, or freeze-thaw exposure. (5.1)
5.2 Insulation shall not be installed against a wet substrate or in a cavity with an active water source until the source is corrected and the substrate is dry.
5.3 Insulation that has become saturated shall be removed and replaced rather than dried in place.
NOTE A batt that has been saturated rarely returns to its installed thickness, and residual moisture in the fiber matrix supports growth on the surface, so drying in place trades a visible defect for a concealed one. (5.4)
5.5 Fill in contact with a recessed luminaire, a flue, a chimney, or another heat-producing item shall be held clear of it by the distance the item's listing requires.
5.6 Where an interior partition is also part of the building envelope, the vapor retarder and air barrier of that assembly shall be provided under Building Thermal InsulationBuilding Thermal InsulationResolves to the current adopted revision.sync/building-thermal-insulation rather than by the acoustic fill or its facing.

6 Tested Assembly Basis

NOTE Sound-rated and fire-rated assemblies are built to a tested design, and the cavity fill is one of the components the design fixes. The fill named in a tested assembly is not a suggestion: a lighter density, a thinner batt, a different fiber family, or a facing the test did not include changes the assembly into one that was not tested. (6.1)
6.2 The tested assembly governing each partition type that receives cavity fill shall be as indicated on the partition schedule.
6.3 The sound transmission class required of each partition type shall be as indicated on the partition schedule.
6.4 The tested assembly governing each floor-ceiling assembly that receives cavity fill shall be as indicated on the floor and ceiling assembly schedule.
6.5 The fire-resistance design governing each rated assembly that receives cavity fill shall be as indicated on the partition and floor-ceiling assembly schedules.
6.6 The sources of tested assembly data accepted on the project shall be as indicated in the datasheet.
Accepted Sources of Tested Assembly Datacheckbox
☑ GA-600 sound-rated designs
☑ UL fire-resistance designs carrying published acoustic ratings
☑ ASTM E90 or ASTM E492 reports from an independent accredited laboratory
☐ Manufacturer-sponsored ASTM E90 or ASTM E492 reports from an accredited laboratory
☐ Published research-institute test catalogs
6.7 Where a cited fire-resistance design lists the cavity insulation as optional, the fill shall be installed to the density and thickness the acoustic assembly requires, and the fire-resistance design shall be confirmed to permit that fill in that thickness before the cavity is closed.
NOTE Many fire-resistance designs list batts as optional, some limit their thickness or fiber family, and a few were tested without any fill, because insulation that holds heat against the fire-side board can shorten the time to failure; the acoustic requirement and the fire requirement therefore have to be checked against the same design rather than assumed compatible. (6.8)
6.9 The Contractor shall not substitute a product of a different fiber family, lesser density, lesser thickness, or different facing for the one a cited tested assembly names without the Architect of Record's written acceptance.
6.10 Where the schedule cites no tested assembly for a partition type that receives fill, the fill shall be the material, minimum density, and thickness recorded in the datasheet for partitions.

7 Cavity Fill Material

7.1 Fiber Family by Application

7.1.1 The fiber family and product form used in partition cavities shall be as indicated in the datasheet.
Partition Cavity Fill Materialselect
Stone wool batt
Slag wool batt
Mineral wool batt, stone or slag
Glass fiber batt
Mineral wool board
Glass fiber board
Polyester fiber batt
Cotton fiber batt
7.1.2 The fiber family and product form used in floor-ceiling cavities shall be as indicated in the datasheet.
Floor-Ceiling Cavity Fill Materialselect
Stone wool batt
Slag wool batt
Mineral wool batt, stone or slag
Glass fiber batt
Mineral wool board
Glass fiber board
Polyester fiber batt
Cotton fiber batt
NOTE No fiber family is the norm across projects, so neither field asserts a default: the choice turns on whether the cited assemblies name a family, whether noncombustibility is required, the cavity heights involved, and the cost the project bears for the stiffer product. (7.1.3)
NOTE Stone wool is spun from molten basalt or similar rock, slag wool from molten blast furnace slag, and the two are sold together in the United States under the mineral wool designation with the same product standards, the same density range, and closely similar acoustic performance; a fire-resistance design that names mineral wool is satisfied by either. (7.1.4)
7.1.5 Where a cited assembly names stone wool specifically, or the datasheet records stone wool, slag wool shall not be substituted for it.
NOTE Mineral wool holds its dimensions at the temperatures reached in a fire test and is stiff enough to stand in a tall cavity without support, which is why fire-resistance designs that require fill usually name it and why it is the family used where a partition cavity is taller than the height at which glass fiber batts sag. (7.1.6)
NOTE Glass fiber batts of the density sold for sound attenuation have airflow resistance in the range that damps a stud cavity, so at equal thickness their contribution to sound transmission class is close to that of mineral wool, and at equal thickness they generally cost less and weigh less; the difference between the families shows up in stiffness, temperature performance, and noncombustibility rather than in transmission loss. (7.1.7)
NOTE Polyester fiber and cotton fiber batts are organic products that reach the surface burning limits of this standard through a treatment rather than through the fiber, and they do not qualify as noncombustible; where the datasheet records either, the surface burning test report shall cover the product in the density and thickness supplied. (7.1.8)
7.1.9 Where the datasheet records a polyester fiber or cotton fiber product, it shall not be installed in an assembly whose cited tested assembly names mineral fiber, and it shall not be installed where the datasheet requires noncombustibility.

7.2 Product Standards by Form

7.2.1 Mineral wool and glass fiber batts for light-frame cavities shall conform to ASTM C665.
7.2.2 Mineral wool and glass fiber blankets for commercial and industrial cavities and for plenum attenuation shall conform to ASTM C553.
7.2.3 Mineral wool and glass fiber board shall conform to ASTM C612.
NOTE An ASTM C665 batt is classified by facing, an ASTM C553 blanket by service temperature and density, and an ASTM C612 board by density and temperature limit, so the type designation the submittal cites is settled by the form and density selected rather than by a separate decision. (7.2.4)
7.2.5 Polyester fiber and cotton fiber batts shall be furnished with third-party test reports for thermal resistance per ASTM C518, surface burning per ASTM E84 or UL 723, and fungi resistance per ASTM C1338 in the density and thickness supplied.

7.3 Noncombustibility

7.3.1 Whether the cavity fill is required to be noncombustible per ASTM E136 shall be as indicated in the datasheet.
Noncombustibility per ASTM E136select
Required for all cavity fill
Required where the cited fire-resistance design names mineral wool or noncombustible fill
Not required
Derived — the fire-resistance designs cited on the assembly schedules and the material limitations the adopted building code places on the building's type of construction (by default)
NOTE Unfaced mineral wool and unfaced glass fiber pass ASTM E136 because the inorganic fiber and the small binder fraction stay below the test's mass loss and temperature rise limits; a kraft, foil, or scrim facing is a combustible layer that the faced product cannot carry through the test. (7.3.2)
NOTE The adopted building code permits combustible insulation, other than foam plastic, in buildings of noncombustible construction where the insulation's flame spread index does not exceed 25, so type of construction alone does not make noncombustibility mandatory; the fire-resistance design cited for the assembly is what usually does. (7.3.3)
7.3.4 Where noncombustibility is required, a faced product, a polyester fiber product, or a cotton fiber product shall not be installed in that assembly.

7.4 Surface Burning

7.4.1 Surface burning characteristics shall be determined per ASTM E84 or UL 723 on the product in the thickness and density supplied.
7.4.2 The surface burning limits the cavity fill shall meet shall be as indicated in the datasheet.
Surface Burning Limits for Cavity Fillradio
● Flame spread index 25 or less and smoke-developed index 50 or less
○ Flame spread index 25 or less and smoke-developed index 450 or less
NOTE The adopted building code sets a flame spread index of 25 and a smoke-developed index of 450 as the limit for insulation concealed in a building of any construction type, while insulation exposed within a plenum is held to a smoke-developed index of 50 under the adopted mechanical code and NFPA 90A; unfaced mineral fiber meets the plenum limit as manufactured, which is why the tighter limit is the one most projects record for all of the fill. (7.4.3)
7.4.4 Fill installed exposed within a plenum shall have a flame spread index of 25 or less and a smoke-developed index of 50 or less regardless of the datasheet selection.
7.4.5 Where a faced product is installed with its facing exposed within a plenum, the faced product as installed shall meet the plenum limit.

7.5 Facing

7.5.1 The facing on cavity fill shall be as indicated in the datasheet.
Insulation Facingradio
● Unfaced
○ Kraft-faced
○ Foil-faced
○ FSK-faced
NOTE A facing on the cavity fill has a small effect on transmission loss, because the porous fill behind it still damps the cavity, but the facing is a combustible membrane, it is the component that fails the noncombustibility test, and it is a vapor retarder placed on whichever side of the cavity the batt happens to face; unfaced fill has none of these consequences, which is why it is the norm for the acoustic function. (7.5.2)
7.5.3 Where the datasheet records a faced product, the facing shall be placed on the side of the cavity that the vapor control design of the assembly requires, as coordinated under Building Thermal InsulationBuilding Thermal InsulationResolves to the current adopted revision.sync/building-thermal-insulation.
7.5.4 Where the facing is intended to serve as the vapor retarder of the assembly, its permeance determined per ASTM E96 shall satisfy the vapor retarder class the adopted building code requires for Climate ZoneClimate ZoneParameterEach project supplies its own value.climate-zone.
7.5.5 A kraft or foil facing shall not be left exposed in an occupied space or in a concealed space in which the adopted building code requires the exposed surface to carry a surface burning classification the faced product does not hold.
7.5.6 Where the datasheet records a faced product and a cited tested assembly names unfaced fill, unfaced fill shall be installed in that assembly.

8 Density and Thickness

8.1 Minimum Density

8.1.1 The minimum nominal density of partition cavity fill shall be as indicated in the datasheet.
Partition Cavity Fill Minimum Nominal Densityrange
pcf
0.50.711.522.53468
8.1.2 The minimum nominal density of floor-ceiling cavity fill shall be as indicated in the datasheet.
Floor-Ceiling Cavity Fill Minimum Nominal Densityrange
pcf
0.50.711.522.53468
NOTE The density ladder spans both fiber families rather than one, so no value on it is the norm and neither field asserts a default. Glass fiber sound attenuation batts are sold between roughly 0.5 and 2.5 pcf, mineral wool batts between 2.5 and 4 pcf, and mineral wool board from 4 pcf up to 8 pcf; a minimum recorded at the low end of the ladder admits either family, and one recorded at 2.5 pcf or above effectively names mineral wool or the heavier glass fiber blankets. (8.1.3)
NOTE In a stud cavity, the contribution of the fill to sound transmission class levels off between roughly 2.5 and 3.5 pcf, and a 6 pcf board in the same cavity delivers close to the same rating as a 3 pcf batt; density above that plateau is bought for dimensional stability in tall cavities, for the fire-resistance design, or for a board product that has to stand on its own, not for transmission loss. (8.1.4)
NOTE Glass fiber batts below roughly 1.5 pcf sag in a vertical cavity taller than the height the manufacturer publishes for unsupported installation, and the void that opens at the top of the cavity costs more transmission loss than the lighter batt saved, so where a light-density product is recorded the retention provisions of this standard carry the weight of the acoustic result. (8.1.5)
8.1.6 Where a cited tested assembly names a density greater than the datasheet minimum, the density the assembly names shall be installed in that assembly.

8.2 Fill Thickness

8.2.1 The fill thickness for each partition type shall be as indicated in the datasheet.
Partition Cavity Fill Thicknessrange
in.
11.522.533.545.568
Per drawings — the partition schedule (deferred by default)
8.2.2 The fill thickness for each floor-ceiling assembly shall be as indicated in the datasheet.
Floor-Ceiling Cavity Fill Thicknessrange
in.
1.52.53.55.5689.510121416
Per drawings — the floor and ceiling assembly schedule (deferred by default)
NOTE Fill thickness follows the cavity of each assembly type, and a project with several stud depths and joist depths has several answers, which is why both thicknesses are recorded per assembly on the schedules rather than once for the project. (8.2.3)
8.2.4 Where the schedule states no fill thickness for a partition type that receives fill, the fill shall be the full depth of the cavity from runner to runner.
8.2.5 Where a cited tested assembly names a thickness less than the cavity depth, the thickness the assembly names shall be installed in that assembly unless the Architect of Record directs a greater thickness in writing.
NOTE A partly filled stud cavity leaves an air layer that still behaves as a spring between the two faces, so the transmission loss of a partial fill falls between an empty cavity and a full one; a partial fill in a floor-ceiling cavity is a different case, because the joist depth usually exceeds what the assembly needs and the tested assemblies for floors were commonly run with a batt thinner than the joist. (8.2.6)
8.2.7 Fill thicker than the cavity depth shall not be installed.
NOTE A batt compressed into a cavity shallower than its nominal thickness performs no better than a batt matched to the cavity, and the excess pushes the face board off the framing, opens the perimeter seal, and leaves the board fasteners without a flat bearing. (8.2.8)

9 Plenum Attenuation

9.1 Plenum Flanking

NOTE Where a partition stops at a suspended ceiling, sound crosses from one room to the next over the partition through the shared plenum, and the ceiling system on each side is the only barrier in that path; the rating of that path is the ceiling attenuation class measured per ASTM E1414, which belongs to the ceiling system and is governed by Suspended Acoustical CeilingsSuspended Acoustical CeilingsResolves to the current adopted revision.sync/suspended-acoustical-ceilings. (9.1.1)
NOTE A partition that stops at the ceiling delivers the transmission loss of the plenum path or of the partition, whichever is lower, so a high sound transmission class in the partition is wasted unless the plenum path is treated to a comparable level or the partition is carried to the structure. (9.1.2)
9.1.3 The partitions that receive plenum attenuation treatment shall be as indicated on the partition schedule.

9.2 Plenum Treatment Selection

9.2.1 The plenum attenuation treatments employed on the project shall be as indicated in the datasheet.
Plenum Attenuation Treatments Employedcheckbox
☐ Blanket laid over the ceiling on each side of the partition
☐ Blanket laid over the full ceiling area of the rooms separated
☐ Mineral wool board plenum barrier from the partition head to the structure
☐ Composite plenum barrier with a limp-mass septum
☐ None
NOTE A blanket laid over the ceiling raises the attenuation of the plenum path by adding absorption above the tile, and it improves the path by a few points at a cost of nothing but material; a plenum barrier closes the path and can bring the plenum route up to the partition's own rating, at the cost of coordinating every duct, pipe, and cable tray that crosses it, each of which needs its own seal to keep the barrier from becoming a leak. (9.2.2)
9.2.3 The material of plenum attenuation blankets shall be as indicated in the datasheet.
Plenum Attenuation Blanket Materialselect
Stone wool blanket
Slag wool blanket
Mineral wool blanket, stone or slag
Glass fiber blanket
Polyester fiber blanket
9.2.4 The width of blanket laid on each side of the partition shall be as indicated in the datasheet.
Plenum Blanket Width Each Side of the Partitionrange
ft
2345681012
Per drawings — the partition type details (deferred by default)
9.2.5 The thickness of plenum attenuation blankets shall be as indicated in the datasheet.
Plenum Attenuation Blanket Thicknessrange
in.
1.522.533.545.56
Per drawings — the partition type details (deferred by default)
9.2.6 Plenum blankets are exposed within the plenum and shall meet the plenum surface burning limit of this standard.

9.3 Plenum Blanket Placement

9.3.1 Blankets laid over a suspended ceiling shall be cut to the ceiling module and placed so that their weight bears on the suspension grid rather than on the face of the tile.
NOTE A blanket bearing on a thin lay-in tile bows the tile within weeks, and the sag it produces in the ceiling line is the defect the Owner sees first. (9.3.2)
9.3.3 Blankets shall be held clear of recessed luminaires, air devices, and other in-plenum equipment by the clearance each item's listing requires, and the gap shall be closed with a fitted piece rather than left open.
9.3.4 Blankets shall be butted tightly at every joint and shall not be stretched to cover an area larger than the blanket.
9.3.5 Where the ceiling suspension system carries a fire-resistance rating, blankets shall be installed only where the ceiling's fire-resistance design permits them.

10 Retention and Attachment

10.1 Partition Cavity Retention

10.1.1 Batts in vertical stud cavities shall be retained by friction between the stud faces, using batts of the width the manufacturer designates for the framing spacing and the framing material.
NOTE Batts for cold-formed steel studs are made wider than the batts for wood studs at the same spacing, because the steel stud flange and the wood stud face leave different clear widths; a wood-stud batt in a steel-stud cavity leaves a gap along one flange, which is a common cause of a partition that fails its field test. (10.1.2)
10.1.3 Field-cut batts shall be cut between 1/2 in. and 1 in. wider than the clear cavity width so that the batt bears against both framing faces.
10.1.4 A batt cut narrower than the cavity shall be replaced rather than wedged in place, and a batt cut more than 1 in. wider than the cavity shall be trimmed rather than buckled into the cavity.
10.1.5 Supplemental retention shall be provided in partition cavities taller than the height indicated in the datasheet.
Partition Height Above Which Supplemental Retention Is Requiredrange
ft
810121416202430
10.1.6 The method of supplemental retention in partition cavities shall be as indicated in the datasheet.
Supplemental Retention Method in Partition Cavitiesselect
Support wires or straps across the cavity
Impaling pins with retaining washers
Insulation retention clips at the framing
Adhesive to the face board
Friction fit alone
NOTE The height at which a friction-fit batt begins to slip is a property of the product's stiffness and density rather than of the framing, so the manufacturer's published unsupported height for the product recorded in the datasheet is the number the threshold is checked against, and the retention field records the method used above it. (10.1.7)
10.1.8 Where the manufacturer's published unsupported height for the product installed is less than the datasheet threshold, the published height shall govern.
10.1.9 Supplemental retention shall not compress the fill below its nominal thickness and shall not penetrate the face board.

10.2 Floor-Ceiling Cavity Retention

10.2.1 Fill in floor-ceiling cavities shall be retained against sagging and displacement by the method indicated in the datasheet.
Floor-Ceiling Cavity Retention Methodselect
Wire insulation supports sprung between the joists
Netting or mesh stapled to the joists
Strapping across the joists
Support on the ceiling membrane or resilient channel
Friction fit alone
10.2.2 The spacing of supports in floor-ceiling cavities shall be as indicated in the datasheet.
Floor-Ceiling Support Spacingrange
in.
121618243248
10.2.3 A batt that rests on the ceiling membrane loads a resilient channel and shorts it against the joist, so where the assembly relies on a resilient channel for its rating the fill shall be held up off the channel unless the cited tested assembly was run with the fill resting on it.
10.2.4 Supports shall hold the fill at the position within the cavity depth that the cited tested assembly shows, whether against the subfloor, against the ceiling, or suspended between.

10.3 Board Attachment

10.3.1 Where the datasheet records a board product, the board shall be attached by the method indicated in the datasheet.
Board Attachment Methodselect
Impaling pins with retaining washers
Adhesive
Friction fit between framing
Wire ties through the framing
Mechanical fasteners with washers
10.3.2 Impaling pins shall be long enough to pass through the board and engage the substrate, and the retaining washer shall hold the board against the substrate without crushing it.
10.3.3 Board attached to a masonry or concrete substrate behind furring shall be attached to the substrate rather than to the furring where the furring is a resilient member.

11 Installation

11.1 Sequence

11.1.1 Cavity fill shall be installed after all in-cavity rough-in, blocking, bracing, and fireblocking is complete and inspected, and before the closing face of the assembly is applied.
11.1.2 Batt and blanket installation in light-frame cavities shall follow ASTM C1320 except where this standard or the cited tested assembly is more stringent.
11.1.3 The Contractor shall schedule the fill so that no trade needs access to a filled cavity before it is closed.
11.1.4 Fill that is displaced, torn, or compressed by later work shall be reinstated before the cavity is closed.

11.2 Fit and Continuity

11.2.1 Fill shall be continuous from runner to runner and from framing face to framing face, without gaps, voids, folds, or compression.
NOTE Field surveys of partitions that fail their field test find incomplete fill more often than any other single cause, and the deficiency is almost always a batt folded behind an obstruction, a cavity left short at the top, or a narrow batt in a steel-stud cavity. (11.2.2)
11.2.3 Batts shall be cut to the cavity length with a knife and fitted flat against the runners without folding.
NOTE A batt folded over at the runner packs the fold to a fraction of its thickness and leaves the runner cavity on the other side of the fold empty, which is the same defect as a short batt with a compressed batt added to it. (11.2.4)
11.2.5 Batts shall be split to pass wires, pipes, conduit, blocking, and bracing so that full thickness is maintained on both sides of the obstruction.
11.2.6 Batts shall be cut to fit around electrical boxes and other in-cavity devices so that the fill bears against the box on every side and is not compressed behind it.
11.2.7 Fill shall extend into the cavity space beside door and window rough openings, behind blocking and backing, and into furred spaces at columns and other irregular conditions.
NOTE The cavity beside a door frame is the last cavity to be filled and the first to be missed, and because door-frame leakage already dominates the flanking of most rated rooms, an empty stud bay beside the frame adds a second path at the weakest point of the partition. (11.2.8)

11.3 Head of Partition

11.3.1 Where the partition extends to the structure, the fill shall extend to the underside of the structure without an unfilled space at the head.
11.3.2 Where the partition has a deflection head, the fill shall extend to the top of the fixed portion of the cavity, and the deflection space shall receive the compressible fill or the joint treatment the cited assembly requires.
11.3.3 Where the partition stops at a suspended ceiling, the fill shall extend to the top of the partition, and the plenum above shall be treated as recorded in this standard for that partition type.
11.3.4 Fill shall not be substituted for the head-of-wall joint system or for firestopping in a fire-resistance-rated assembly, which are governed by FirestoppingFirestoppingResolves to the current adopted revision.sync/firestopping.

11.4 Coordination with Perimeter Seal and Penetrations

NOTE Cavity fill and the perimeter acoustic seal of the partition depend on each other, because fill damps the cavity and the seal closes the air paths around the faces, and a partition with either one alone tests well below its rating. (11.4.1)
11.4.2 The Contractor shall coordinate the timing of fill with the application of acoustic sealant at the runners, the perimeter, and the penetrations under Gypsum Board AssembliesGypsum Board AssembliesResolves to the current adopted revision.sync/gypsum-board-assemblies, so that the fill is in place before the closing face is sealed.
11.4.3 Fill shall be installed continuously up to each penetration and shall not disturb an installed firestop system.
11.4.4 Where a firestop system is installed after the fill, the Contractor shall reinstate the fill around the penetration before the cavity is closed.
NOTE Back-to-back electrical boxes in one stud bay pass sound through the partition regardless of the fill, and the box offset and the putty pads that close that path are governed by Gypsum Board AssembliesGypsum Board AssembliesResolves to the current adopted revision.sync/gypsum-board-assemblies. (11.4.5)

12 Field Acoustic Testing

12.1 Testing Requirement

12.1.1 Field acoustic testing of completed assemblies shall be as indicated in the datasheet.
Field Acoustic Testingradio
● Not required
○ ASTM E336 testing by an independent agency retained by the Contractor
○ ASTM E336 testing by an independent agency retained by the Owner
12.1.2 The assemblies subject to field testing shall be as indicated in the datasheet.
Assemblies Subject to Field Testingcheckbox
☐ Each acoustically rated partition type
☐ Each partition type at or above the threshold sound transmission class
☐ Each acoustically rated partition type on each floor
☐ Each acoustically rated floor-ceiling assembly type
12.1.3 The laboratory sound transmission class at or above which a partition type is subject to field testing shall be as indicated in the datasheet.
Minimum Laboratory STC of Partition Types Subject to Field Testingrange
STC
404550556065
NOTE Field testing verifies the whole assembly and its flanking paths, most of which are outside this standard, so the party that pays for the test and the party responsible for a failure are not always the same; the testing field records who retains the agency, and the corrective action article assigns the cost by cause. (12.1.4)

12.2 Field Ratings and Acceptance

12.2.1 The field ratings reported for tested assemblies shall be as indicated in the datasheet.
Field Ratings Reportedcheckbox
☑ Apparent sound transmission class per ASTM E336
☐ Noise isolation class per ASTM E336
☐ Normalized noise isolation class per ASTM E336
☐ Apparent impact insulation class per ASTM E1007
12.2.2 The permitted shortfall of the field rating below the laboratory rating of the cited assembly shall be as indicated in the datasheet.
Permitted Shortfall of the Field Rating Below the Laboratory Ratingrange
points
12345
NOTE A field measurement includes every flanking path the laboratory specimen did not have, so field ratings run several points below the laboratory rating of the same assembly; the adopted building code sets the minimum field rating for assemblies between dwelling and sleeping units five points below the laboratory minimum, and that allowance is the reason the default here is five. (12.2.3)
12.2.4 The acceptance criterion for each tested assembly shall be the laboratory rating of the cited assembly less the permitted shortfall, and the laboratory rating shall not itself be the field acceptance criterion.
12.2.5 Where a rating is required by the adopted building code, the field acceptance criterion shall not be less than the field rating the code requires.

12.3 Testing Conditions

12.3.1 Field tests shall be performed by an independent testing agency experienced in field measurement under ASTM E336 and, where impact tests are required, under ASTM E1007.
12.3.2 Tests shall be performed after the perimeter seal, the penetrations, the doors, and the adjacent finishes of the tested assembly are complete, and a test performed before that point shall not be the basis of acceptance.

12.4 Corrective Action

12.4.1 Where a tested assembly does not meet its acceptance criterion, the Contractor shall investigate the cause, correct it, and retest the assembly.
NOTE The most common causes of a failed field test are incomplete cavity fill, a broken perimeter seal, back-to-back or unsealed electrical boxes, an untreated plenum path, and door-frame leakage, and a diagnostic measurement that locates the path is usually cheaper than reopening the partition on a guess. (12.4.2)
12.4.3 The cost of investigation, correction, and retesting shall be borne by the Contractor where the cause lies in the work under this standard or under another standard in the Contractor's scope, and by the Owner where the cause lies in the design of the assembly or in a flanking path the contract documents did not address.
12.4.4 Where the parties disagree on the cause of a failed test, the Architect of Record shall make the initial determination.

13 Mock-Ups

13.1 The mock-up requirement for partition types shall be as indicated in the datasheet.
Mock-Up Requirementradio
● Not required
○ One mock-up of each acoustically rated partition type
○ One mock-up of each partition type at or above the threshold sound transmission class
13.2 The laboratory sound transmission class at or above which a partition type requires a mock-up shall be as indicated in the datasheet.
Minimum Laboratory STC of Partition Types Requiring a Mock-Uprange
STC
4550556065
NOTE A mock-up of a high-rating partition lets the fill, the perimeter seal, the box treatment, and the head condition be reviewed together at one location before the same details are repeated across a floor, and where field testing is also required a tested mock-up finds a systemic defect at one partition instead of at fifty. (13.3)
13.4 Each mock-up shall include the framing, the cavity fill, every board layer, the accessories, and the perimeter seal of the partition type it represents, built in a location and to a size the Architect of Record accepts.
13.5 The closing face of the mock-up shall not be applied until the fill has been reviewed.
13.6 Where field testing is required, the mock-up may be tested under this standard and, where it passes, may remain as part of the work.
13.7 A mock-up that does not represent the cited assembly or does not pass its review shall be corrected or rebuilt at the Contractor's expense before production partitions of that type are closed.

14 Delivery, Storage, and Handling

14.1 Insulation shall be delivered in the manufacturer's packaging with labels intact.
14.2 Bundles shall be stored indoors, off the floor, and protected from water, from crushing, and from sunlight.
14.3 Temporary storage outdoors shall be under cover on a raised platform, and bundles stored outdoors shall be brought under roof before the packaging is opened.
14.4 Mineral wool that has been wetted and shows no crushing, compression set, or growth may be dried and installed; mineral wool showing any of those conditions shall be rejected.
14.5 Glass fiber, polyester fiber, or cotton fiber batts that have been wetted shall be rejected.
NOTE Water softens the binder in a glass fiber batt and the batt does not recover its thickness on drying, while a mineral wool batt sheds water and holds its shape unless it was crushed while wet, which is why the two are treated differently on delivery. (14.6)
14.7 Bundles shall remain wrapped until they are brought to the point of installation, and a bundle opened at the end of a shift shall be returned to enclosed storage.
14.8 Compressed packaging shall be opened far enough ahead of installation for the batts to recover their nominal thickness.

15 Warranty

15.1 The Contractor shall warrant the acoustic insulation installation against defects in materials and workmanship, including incomplete fill, sagged or displaced fill, compressed fill, and unfilled space around obstructions, for the period indicated in the datasheet, measured from the date of substantial completion.
Installation Warranty Periodrange
years
1235
15.2 Where the contract documents state a longer warranty period than the datasheet, the longer period shall govern.
15.3 The Contractor's cost of a warranty correction shall include opening and closing the assembly, reinstating the fill, restoring any firestop system or perimeter seal disturbed, refinishing the face, and retesting where the assembly was field tested.
15.4 Work performed under this warranty shall itself be warranted for a full new term equal to the original period measured from the date the correction is completed, or for the remainder of the original period, whichever ends later.
15.5 The warranty shall not cover fill disturbed by others after acceptance, fill wetted by a water source that arose after acceptance, or fill removed during post-occupancy work and not reinstated.
15.6 Where the Contractor observes a condition during installation that will shorten the life of the fill, including water entry, an unconditioned interior, or another trade disturbing installed fill, the Contractor shall report it to the Architect of Record in writing before the affected cavity is closed.

Edit this page

SynC Standards are reference material provided for informational purposes only and as a guide. They are not engineering, architectural, or legal advice and are not a substitute for the judgment of a licensed design professional. It is the responsibility of the user to determine the applicability of any standard to a specific project and to verify all requirements against the governing codes, manufacturer data, and project conditions. SynC does not render professional services and forms no professional relationship by publishing this content. Provided "as is," without warranty of any kind, including fitness for a particular purpose. See our Terms of Use for the complete terms. Moderation log.

This standard is published by SynC and licensed under Creative Commons Attribution-ShareAlike 4.0. You may share and adapt it, including commercially, provided you give credit, link to the license, indicate any changes, and license your adaptations under the same terms. Keep the attribution and notice below with any copy — it includes the warranty disclaimer the license requires you to retain.

Attribution & reuse notice — keep this with any copy:
"Acoustic Insulation." SynC Standards. Licensed under CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/). Source: https://synergyinconstruction.com/wiki/sync/acoustic-insulation — reference material only; not professional engineering advice and provided without warranty. Verify against governing codes and have a licensed professional review before use.