1 Scope
NOTE This standard governs the selection, specification, and installation of sound-absorbing insulation installed within concealed cavities of interior partitions, suspended ceiling plenums, and floor/ceiling assemblies for the purpose of attenuating airborne sound transmission between adjacent spaces. (1.1)
NOTE The materials covered are unfaced mineral fiber blanket and batt (stone wool and slag wool), unfaced glass fiber blanket and batt, and mineral fiber board, in the densities and thicknesses commonly used as cavity infill in commercial construction. (1.2)
NOTE Acoustic insulation is one component of an acoustic assembly. (1.3)
NOTE The sound transmission class (STC) of a partition or floor/ceiling is the property of the entire system — the gypsum board layers, the framing, the cavity insulation, the perimeter sealing, and any decoupling elements such as resilient channel, all combine to produce the tested rating. (1.4)
1.5 The Contractor shall install the insulation type, density, and thickness specified in the referenced tested assembly without substitution.
1.6 The Contractor shall coordinate the cavity infill with Gypsum Board Assemblies for partitions and with the applicable floor and ceiling specifications. NOTE Substituting a different insulation density, thickness, or material than the one in the tested assembly can change the STC by several points and may push a partition below the design intent. (1.7)
NOTE Acoustic insulation in a stud cavity contributes to STC primarily by damping the cavity resonance: filling the cavity with porous, fibrous insulation introduces flow resistance that absorbs standing-wave energy, broadening and lowering the resonance and improving transmission loss across most of the speech frequency range. (1.8)
NOTE The acoustic mechanism is friction in the fiber matrix, not mass, which is why a 2.5 pcf and a 6.0 pcf stone wool batt produce nearly the same STC contribution in a typical stud-wall cavity; in most stud-wall and ceiling-plenum applications the density at which incremental improvement falls off is between 2.5 and 3.5 pcf. (1.9)
1.10 The Contractor shall coordinate with Gypsum Board Assemblies for the partition design number that drives material, density, and thickness selection. 1.11 The Contractor shall coordinate with Firestopping for penetration-firestopping where acoustic insulation occurs in fire-resistance-rated assemblies. 1.12 Where a single insulation product is intended to serve both thermal and acoustic purposes within the building envelope, the requirements of Building Thermal Insulation shall govern. 1.13 The Contractor shall coordinate with Doors Frames And Hardware for acoustic seals and gasketing at door and frame perimeters in acoustically rated partitions, because door-frame leakage is the dominant flanking path in most rated rooms. 2 Referenced Standards
2.1 Materials and installation shall comply with the latest edition of each of the following standards adopted by the Authority Having Jurisdiction.
| Standard |
Title |
| ASTM C665 |
Standard Specification for Mineral-Fiber Blanket Thermal Insulation for Light Frame Construction and Manufactured Housing (Type I unfaced applicable) |
| ASTM C612 |
Standard Specification for Mineral Fiber Block and Board Thermal Insulation |
| ASTM C553 |
Standard Specification for Mineral Fiber Blanket Thermal Insulation for Commercial and Industrial Applications |
| ASTM C518 |
Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus |
| ASTM C411 |
Standard Test Method for Hot-Surface Performance of High-Temperature Thermal Insulation |
| ASTM C795 |
Standard Specification for Thermal Insulation for Use in Contact with Austenitic Stainless Steel |
| ASTM C1338 |
Standard Test Method for Determining Fungi Resistance of Insulation Materials and Facings |
| ASTM E84 |
Standard Test Method for Surface Burning Characteristics of Building Materials |
| ASTM E90 |
Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements |
| ASTM E413 |
Classification for Rating Sound Insulation |
| ASTM E1414 |
Standard Test Method for Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum |
| ASTM E336 |
Standard Test Method for Measurement of Airborne Sound Attenuation Between Rooms in Buildings |
| ASTM E1332 |
Standard Classification for Rating Outdoor-Indoor Sound Attenuation |
| ASTM E136 |
Standard Test Method for Assessing Combustibility of Materials Using a Vertical Tube Furnace at 750 °C |
| IBC |
International Building Code (current edition adopted by jurisdiction) |
| NFPA 101 |
Life Safety Code (corridor and separation wall acoustic and fire requirements) |
| UL Fire Resistance Directory |
UL Fire-Resistance Rated Systems |
2.2 Where the contract documents, the adopted building code, or a referenced standard impose conflicting requirements, the more stringent shall govern unless the Architect of Record directs otherwise in writing.
3 Submittals
3.1 Action Submittals
3.1.1 The Contractor shall submit the following for the Architect's review before procurement and installation:
- Product data for each acoustic insulation type, including material composition (stone wool, slag wool, or glass fiber), nominal density, thickness range, dimensional tolerances, and applicable ASTM product designation
- ASTM E84 surface burning test report for each insulation product, showing flame spread index (FSI) and smoke developed index (SDI)
- ASTM E136 noncombustibility classification where required by the project's construction type or by the applicable fire-resistance design number
- Third-party laboratory test reports per ASTM E90 demonstrating the STC contribution of the proposed insulation in assemblies matching the project's tested partition designs, where the cavity-fill material is the specific insulation product proposed
- Identification of the specific UL or GA-600 design number under which the insulation will be used, cross-referenced to each acoustically and fire-rated partition type designation
- Manufacturer's installation instructions, including friction-fit retention guidance, recommendations for plenum and floor cavity attachment, and any limitations on cavity orientation
- Sample of each insulation product proposed, minimum 12 inches × 12 inches, for verification of density, facing (if any), and dimensional consistency
☑ Product data for each acoustic insulation type
☐ ASTM E84 surface burning test report
☐ ASTM E136 noncombustibility classification (where required)
☐ ASTM E90 laboratory STC test reports for cited assemblies
☐ Fire-resistance design number cross-reference schedule
☐ Manufacturer installation instructions
☐ Product samples
3.1.2 The Contractor shall submit the action submittal items listed above for the Architect's review before procurement and installation.
3.1.3 Installation of acoustic insulation in any rated assembly shall not begin until the corresponding submittals have been reviewed and returned.
3.2 Closeout Submittals
3.2.1 The Contractor shall provide the following at project closeout:
- Certificate of compliance signed by the Contractor stating that all acoustic insulation was installed in conformance with the approved submittals, manufacturer's instructions, and this standard
- Field test reports for STC or noise isolation class (NIC) verification testing where specified
- Warranty documentation for products carrying a manufacturer warranty
☑ Certificate of compliance signed by the Contractor
☑ Field test reports for STC or NIC verification (where specified)
☑ Warranty documentation for products carrying a manufacturer warranty
3.2.2 The Contractor shall provide the closeout submittal items listed above at project closeout.
4 Quality Assurance
4.1 Installer Qualifications
NOTE Insulation contributes meaningfully to STC only when it fills the cavity continuously and without compression. (4.1.1)
4.1.2 Acoustic insulation shall be installed by workers experienced in commercial cavity-insulation work and familiar with the requirements of tested acoustic and fire-resistance design numbers.
4.1.3 Installers shall be trained in the splitting, fitting, and friction-fit techniques that achieve complete cavity coverage around wiring, blocking, electrical boxes, and other obstructions.
4.2 Pre-Installation Coordination
4.2.1 Before acoustic insulation installation begins in rated assemblies, the Contractor shall confirm with the Architect that the insulation type, density, and thickness match the specific tested assembly design number referenced on the drawings.
4.2.2 Substitution of a lighter density, a different fiber type, or a thinner product than the tested configuration shall not be made without written approval.
4.2.3 The Contractor shall coordinate the insulation work with the framing, electrical rough-in, plumbing, and other trades whose cavity penetrations will be in place before the cavity is closed.
4.2.4 Insulation installed before all in-cavity work is complete is invariably disturbed and shall be inspected after final rough-in.
4.3 Field Inspection of Rated Assemblies
4.3.1 Acoustic insulation in fire-resistance-rated or acoustically rated assemblies shall be available for inspection by the Authority Having Jurisdiction and the Owner's representative before the second face of the partition is closed with gypsum board.
4.3.2 The Contractor shall not close any rated assembly cavity until the cavity insulation has been inspected and released, or until written permission to proceed has been issued.
4.3.3 Pre-Closing Inspection of Cavity Insulation
● Required for all rated assemblies
○ Required for STC 50 and higher assemblies only
○ Not required (non-rated assemblies)
4.4 Listing and Labeling
4.4.1 All acoustic insulation products shall bear the manufacturer's label identifying the product name, the applicable ASTM standard, the type or class designation, and the nominal density.
4.4.2 Labels shall remain on bundles delivered to site and on at least one batt from each opened bundle until installation is complete.
4.4.3 Unlabeled or unidentifiable insulation shall be rejected.
5 Environmental and Service Conditions
5.1 Temperature and Humidity at Installation
5.1.1 Acoustic insulation may be installed at any temperature within the manufacturer's stated range and is not affected by ambient humidity in the same way that joint compound or adhesive products are.
5.1.2 Insulation shall not be installed against wet substrates or in cavities subject to active water intrusion.
5.1.3 Mineral fiber and glass fiber that becomes saturated loses dimensional stability and shall be removed and replaced.
NOTE Drying wet insulation in place is not acceptable, because residual moisture in the fiber matrix supports microbial growth and the insulation typically does not return to its installed dimension. (5.1.4)
5.2 Service Conditions
NOTE Acoustic cavity insulation is intended for installation in dry, conditioned interior spaces. (5.2.1)
NOTE Use of these products in cavities subject to repeated wetting, condensation, or freeze-thaw cycling is outside the scope of this standard. (5.2.2)
5.2.3 Where the building envelope assembly is also the host for acoustic insulation, vapor management shall follow Building Thermal Insulation and the higher-density mineral wool products typical of envelope use shall be specified. 5.3 Fungi Resistance
NOTE Mineral fiber and glass fiber insulation are inherently inorganic and do not provide food for fungal growth; however, contamination of the fiber surface by dust, organic debris, or moisture can support growth on the surface, so maintaining a dry, clean cavity is the primary defense. (5.3.1)
5.3.2 Acoustic insulation products specified for use in healthcare, food-service, and other moisture-sensitive occupancies shall be tested for fungi resistance per ASTM C1338 and shall not support fungal growth under the test conditions.
5.3.3 Fungi Resistance Documentation
○ ASTM C1338 test report required
● Manufacturer certification of inorganic composition acceptable
○ Not required
6 Materials
6.1 General Material Requirements
6.1.1 All acoustic insulation shall be new, dry, undamaged, and free of compression set, oil, dust, or other contamination at time of installation.
6.1.2 Bundles that have been wetted, crushed in transit, or stored improperly shall be inspected and replaced where the fiber matrix has been disturbed.
6.1.3 Insulation shall be stored indoors in a dry, climate-controlled location, off the ground, and protected from weather, mechanical damage, and UV exposure until immediately before installation.
6.1.4 Plastic shipping wrap shall remain in place until the bundle is brought to its point of installation.
6.2 Stone Wool (Mineral Wool, Rock Wool)
NOTE Stone wool insulation is manufactured by melting basalt or other igneous rock together with a binder and spinning the molten material into fine fibers. (6.2.1)
NOTE The resulting product is inorganic, noncombustible, dimensionally stable at elevated temperature, and naturally water-shedding rather than water-absorbing. (6.2.2)
6.2.3 Stone wool batt and blanket for cavity-infill acoustic use shall conform to ASTM C665 (Type I, unfaced) where used in light-frame stud cavities, or to ASTM C553 for industrial and commercial blanket applications.
6.2.4 Mineral wool board (semi-rigid and rigid) shall conform to ASTM C612.
NOTE Stone wool is the default acoustic cavity-fill material for commercial gypsum-board partition assemblies in this standard because of its effective acoustic absorption at modest densities, noncombustibility per ASTM E136, friction-fit retention in vertical cavities, dimensional stability, and resistance to settling. (6.2.5)
NOTE Stone wool batts are dimensionally stiffer than glass fiber and hold their shape in tall partition cavities, masonry cavity walls, and ceiling-plenum applications where glass fiber would sag or compress over time. (6.2.6)
6.3 Slag Wool
NOTE Slag wool is manufactured from blast furnace slag using the same melt-and-spin process as stone wool. (6.3.1)
NOTE The fiber properties, density range, and acoustic performance are similar to stone wool, and slag wool products in the U.S. market are typically marketed under the broader "mineral wool" designation alongside stone wool. (6.3.2)
6.3.3 Slag wool shall conform to the same ASTM C665, C553, or C612 designations that apply to stone wool products and may be used wherever stone wool is specified, unless the contract documents specifically require stone wool.
6.3.4 Where the project specification or design number cites "mineral wool" without further qualification, either stone wool or slag wool meeting the cited ASTM standard is acceptable.
6.4 Glass Fiber (Fiberglass)
NOTE Glass fiber insulation is manufactured by melting silica sand and recycled glass and spinning the molten material into fine fibers, bound together with a binder resin. (6.4.1)
NOTE Glass fiber is the most economical acoustic cavity-fill material and is appropriate for the majority of non-rated and lower-STC commercial partitions. (6.4.2)
6.4.3 Unfaced glass fiber batt and blanket for cavity-infill acoustic use shall conform to ASTM C665 (Type I, unfaced) for light-frame construction or to ASTM C553 for commercial and industrial blanket.
6.4.4 Faced glass fiber products that include kraft or foil facings introduce combustible material and are not appropriate where ASTM E136 noncombustibility is required.
NOTE Glass fiber batts in low-density configurations (0.5 to 1.5 pcf) are less dimensionally stiff than mineral wool and may sag over time in tall vertical cavities or in plenum applications unless they are mechanically retained. (6.4.5)
NOTE Heavier-density glass fiber blanket products (2.0 pcf and above) approach mineral wool in dimensional stability and are appropriate for most commercial partition cavities. (6.4.6)
6.4.7 Material and Designation Selection
● Stone wool (basalt mineral wool)
○ Slag wool
○ Glass fiber (fiberglass)
● ASTM C665 Type I (unfaced batt and blanket, light frame)
○ ASTM C553 (commercial/industrial blanket)
○ ASTM C612 (mineral fiber block and board)
Per drawings
6.5 Facing
NOTE Vapor-retarder facings (kraft, foil, or vinyl) interrupt the porous flow path that produces acoustic absorption, have a small but measurable effect on the cavity's transmission loss, and introduce combustible material into the cavity that is generally not compatible with the noncombustibility requirements of rated assemblies. (6.5.1)
6.5.2 Acoustic cavity-fill insulation in interior partitions, ceiling plenums, and floor cavities shall be unfaced.
6.5.3 Where vapor management is required by the assembly, the Contractor shall coordinate with Building Thermal Insulation for the placement of a separate vapor retarder layer and shall use an unfaced acoustic product for the cavity-fill function. 6.5.4 Insulation Facing
● Unfaced (standard for cavity acoustic use)
○ Foil-faced (only where vapor retarder integration is specifically required)
○ Kraft-faced (only where vapor retarder integration is specifically required)
7 Density and Thickness
7.1 Density Selection
NOTE For acoustic cavity-fill in stud-framed partitions, ceiling plenums, and floor/ceiling assemblies, the relationship between density and STC contribution flattens above approximately 2.5 pcf. (7.1.1)
7.1.2 The default density for general acoustic partition infill shall be 3.0 pcf stone wool, which provides the acoustic flow resistance required for full cavity damping without the cost and weight penalty of heavier products.
7.1.3 Lower densities (1.5 to 2.5 pcf) are acceptable for non-rated and moderately rated assemblies (up to STC 45) and are commonly used with glass fiber products.
7.1.4 Higher densities (4.0 to 6.0 pcf) shall be specified where the tested assembly design number requires that density, where the insulation also serves a fire-resistance protection role, or where the insulation will be exposed to elevated temperatures requiring documented performance per ASTM C411.
7.1.5 Nominal Density Selection
1.5 pcf (glass fiber, non-rated and STC ≤ 40 partitions)
2.5 pcf (stone wool or glass fiber, STC up to 45)
3.0 pcf (stone wool, standard commercial partition default)
4.0 pcf (stone wool, fire-rated or higher-STC assemblies)
6.0 pcf (stone wool board, semi-rigid applications)
Per drawings
7.2 Thickness Selection
7.2.1 The default thickness of cavity-fill acoustic insulation shall be the full depth of the stud cavity, runner to runner.
NOTE Partial-fill insulation reduces the acoustic benefit, because the unfilled portion of the cavity continues to behave as an air spring and supports the resonance the insulation is intended to suppress. (7.2.2)
7.2.3 Additional thickness beyond the cavity depth provides no benefit and shall not be installed, because compressed insulation in a thinner cavity than its nominal dimension performs no better than insulation matched to the cavity depth and may deflect the framing or interfere with face-board attachment.
7.2.4 Cavity Fill and Thickness Selection
● Full-depth fill (matches stud or joist depth) — default
○ Partial-fill (specific tested assembly only)
Per drawings
1-1/2 in (2-1/2 in stud depth, partial use)
2-1/2 in (2-1/2 in stud cavity, full fill)
3-1/2 in (3-5/8 in stud cavity, full fill)
4 in (4 in stud cavity, full fill)
6 in (6 in stud cavity, full fill)
Per drawings — partition type schedule
8.1 Mechanism
NOTE The acoustic benefit of cavity insulation derives from porous absorption — the conversion of acoustic energy to heat as air oscillates through the fiber matrix. (8.1.1)
NOTE This mechanism is most effective in the speech-intelligibility frequency range (approximately 125 Hz to 4000 Hz) that drives the STC rating. (8.1.2)
NOTE The insulation does not add mass, does not stiffen the partition, and does not decouple the two face layers; those functions are performed by the gypsum board, the framing, and accessories such as resilient channel. (8.1.3)
NOTE In a typical single-stud gypsum-board partition with two layers of 5/8-inch board on each side and 3-1/2-inch stone wool fill, the cavity insulation contributes approximately 4 to 7 STC points compared to the same partition with an empty cavity. (8.1.4)
8.2 STC Contribution
NOTE A correctly executed full-cavity-fill of unfaced mineral fiber raises a typical commercial partition's STC by 4 to 7 points. (8.2.1)
NOTE The benefit is reduced where the insulation is partially compressed, partially missing, or sagging. (8.2.2)
NOTE Field surveys consistently identify incomplete cavity fill as the single most common cause of partitions that test below their design STC. (8.2.3)
8.2.4 Specified Partition Rating and Tested Assembly Reference
Not rated (no acoustic insulation required)
STC 40
STC 45
STC 50
STC 55
STC 60 or higher
Per drawings
● GA-600 sound-rated design
○ UL classified design with acoustic data
○ Published independent laboratory ASTM E90 test report
○ Not applicable (non-rated assembly)
Per drawings
8.3 Plenum and Ceiling-to-Ceiling Attenuation
NOTE Where partitions terminate at the suspended ceiling rather than extending to the structure above, sound passes over the partition through the shared ceiling plenum. (8.3.1)
NOTE The plenum-attenuation performance of the combined ceiling-and-partition is tested per ASTM E1414 and is reported as the ceiling attenuation class (CAC). (8.3.2)
8.3.3 Where the partition is intended to provide meaningful acoustic separation, the partition shall be extended to the structure above and the plenum-flanking path eliminated.
8.3.4 Where the partition terminates at the ceiling, the plenum portion shall receive a sound-isolating treatment specified on the drawings, which may include batts laid over adjacent ceiling tiles on each side of the partition, or a plenum barrier extending from the top of the partition to the deck above.
8.3.5 Partition Termination and Plenum Treatment
● Deck-to-deck (partition extends to structure)
○ Ceiling height (terminates at suspended ceiling)
○ Ceiling height with plenum barrier above
Per drawings
○ Batt insulation laid over adjacent tiles each side of partition
○ Continuous plenum barrier from top of partition to deck
○ None (no special treatment)
● Not applicable (deck-to-deck partition)
Per drawings
9.1 General Fire Requirements
9.1.1 Acoustic insulation installed in fire-resistance-rated partition or ceiling assemblies shall be the type, density, and thickness specified in the tested design.
NOTE Substituting a different product can invalidate the rating. (9.1.2)
NOTE Mineral wool products are commonly required in higher-hour rated assemblies because their dimensional stability at elevated temperature contributes to the assembly's continued performance during a fire test; glass fiber products are acceptable in many lower-hour rated assemblies and in non-rated partitions. (9.1.3)
9.2 Surface Burning
NOTE Unfaced mineral wool and unfaced glass fiber typically achieve a Class A classification (FSI ≤ 25, SDI ≤ 50) without difficulty because the inorganic fiber does not propagate flame across its surface. (9.2.1)
9.2.2 Acoustic insulation shall be tested per ASTM E84 for surface burning characteristics.
9.2.3 Class A classification is the default and is required for all interior cavity-fill applications regulated by the IBC.
9.2.4 ASTM E84 Surface Burning Classification
● Class A — FSI ≤ 25, SDI ≤ 50 (required)
○ Class B — FSI 26–75 (not acceptable for cavity-fill in rated assemblies)
○ Not applicable (product not exposed to interior)
9.3 Noncombustibility
NOTE Stone wool, slag wool, and unfaced glass fiber typically meet ASTM E136 because the inorganic fiber and any small fraction of organic binder are below the combustibility thresholds in the test. (9.3.1)
9.3.2 Where the project's construction type or the cited fire-resistance design requires noncombustible materials, the acoustic insulation shall be classified noncombustible per ASTM E136.
9.3.3 Faced products (kraft or foil facings) contain organic material, do not meet ASTM E136, and shall not be substituted where noncombustibility is required.
9.3.4 ASTM E136 Noncombustibility Requirement
● Required (IBC Type I or II construction, or rated design requires)
○ Not required
Per drawings
9.4 Hot Surface and Continuous Service Temperature
NOTE Mineral wool products are typically rated for continuous service temperatures of 1200 °F or higher; glass fiber products are typically rated for 350 °F. (9.4.1)
NOTE In ordinary partition cavities at room temperature, ASTM C411 documentation is not required. (9.4.2)
9.4.3 Where acoustic insulation will be in contact with surfaces operating above ambient temperature — for example, adjacent to recessed light fixtures, behind chimneys or flues, or in service-temperature applications — its performance shall be evaluated per ASTM C411.
9.5.1 This requirement is rare in cavity-fill acoustic applications but shall be addressed if specified.
9.5.2 Where insulation will be in direct contact with austenitic stainless steel, the product shall comply with ASTM C795 to limit leachable chlorides, fluorides, sodium, and silicates that could cause stress corrosion cracking of the stainless steel.
10 Accessories
10.1 Retention in Vertical Cavities
10.1.1 Mineral wool and stiff-blanket glass fiber batts in vertical stud cavities shall be retained by friction fit, with the batt width sized 1/2 to 1 inch wider than the stud spacing so the batt compresses slightly into the cavity and is held by friction against the stud faces.
10.1.2 In tall partitions (over 12 feet), in cavities exposed to vibration, or where settlement of softer glass fiber products is a concern, supplemental retention shall be provided.
10.1.3 Stud Cavity Retention Method
● Friction fit (default for stone wool and stiff blanket products)
○ Friction fit + horizontal support strips at floor lines (tall cavities)
○ Insulation clips at cavity perimeter
○ Self-adhering insulation backing
Per drawings
10.2 Retention in Ceiling and Floor Cavities
10.2.1 Insulation laid above suspended ceilings or installed within floor/ceiling joist cavities shall be retained against displacement and sag.
10.2.2 Insulation supports in floor/ceiling cavities shall be wire support rods, plastic mesh, or strapping installed at 18 inches on center maximum across the underside of the cavity.
10.2.3 Insulation laid above suspended ceiling tiles shall be sized to match the tile module so it bears on the grid rather than on the tile face.
NOTE Insulation that bears on the face of a thin tile may produce visible sag in the ceiling line over time. (10.2.4)
10.2.5 Floor/Ceiling Cavity Retention
● Wire support rods at 18 in o.c. (standard for batts in floor joist cavities)
○ Plastic mesh or strapping at 18 in o.c.
○ Self-adhering blanket
○ Not applicable
Per drawings
10.3 Mechanical Fasteners for Board Products
10.3.1 Mineral wool board installed within partition or ceiling cavities for high-performance acoustic applications shall be retained by mechanical impalement pins, adhesive, or wire ties as specified by the tested assembly.
10.3.2 Impalement pins shall be of length suitable to penetrate the board thickness and engage the substrate, and shall be capped with locking washers that hold the board against the substrate.
10.3.3 Mineral Wool Board Attachment
● Friction fit between studs (most common)
○ Impalement pins with locking washers
○ Adhesive applied to substrate
○ Wire ties through framing
○ Not applicable (batt or blanket product)
11 Installation
11.1 General Installation Requirements
NOTE Cavity-fill insulation is one of the most commonly compromised elements in partition construction because the work is concealed and feedback on its quality is slow. (11.1.1)
11.1.2 Acoustic insulation shall be installed after all rough-in work within the cavity is complete and inspected — including electrical conduit and boxes, plumbing, low-voltage cabling, in-wall bracing, and any required fire-blocking — and before the second face of the partition is closed with gypsum board.
11.1.3 The Contractor shall coordinate the timing of insulation installation so that no further trades require access to the cavity after insulation is in place.
11.1.4 Cavities that are reopened after insulation is installed shall be re-inspected and the insulation re-fitted.
11.1.5 The insulation shall fill the cavity continuously from runner to runner and from stud face to stud face without compression, gaps, or voids.
11.1.6 The Contractor shall treat the insulation work with the same care given to the visible face layers.
11.2 Splitting Around Obstructions
NOTE A batt simply folded behind a wire or compressed around an electrical box leaves a localized void that disproportionately reduces the partition's acoustic and fire performance. (11.2.1)
11.2.2 Wires, pipes, blocking, fire-stops, and electrical boxes within the cavity shall be accommodated by splitting the insulation so that both sides of the obstruction are filled.
11.2.3 The Contractor shall split each batt to the depth required to wrap the obstruction front and back, taking care to maintain full thickness on both sides.
11.2.4 Splitting of Insulation Around Cavity Obstructions
● Required at all wires, pipes, blocking, fire-stops, and boxes
○ Discretionary
Per drawings
11.3 Friction Fit and Sizing
11.3.1 Batts shall be sized 1/2 to 1 inch wider than the stud spacing so they compress slightly into the cavity and friction-fit between the studs.
11.3.2 Batts cut narrower than the cavity width shall not be force-fit by wedging; they shall be replaced with correctly sized batts.
11.3.3 Batts wider than 1 inch over the cavity width shall be trimmed, because excess width that buckles into the cavity creates internal voids and prevents the face board from sitting flush against the studs.
11.3.4 Batt Width Relative to Stud Spacing
● Match stud spacing nominal width (16 in stud — 15 in batt; 24 in stud — 23 in batt)
○ Slightly oversized batt for tighter friction fit (per manufacturer's recommendation)
11.4 Cutting and Fitting at Top and Bottom of Cavity
NOTE Folded batts at runners create local compression that reduces the effective cavity depth and provides poorer absorption than a flat-cut batt fitted snugly to the runner. (11.4.1)
11.4.2 Batts at the top and bottom of the cavity shall be cut to the cavity length and fitted without fold-over or compression.
11.4.3 The Contractor shall use a sharp utility knife or insulation knife to cut batts cleanly, because tearing batts produces a ragged edge that does not seat well against framing.
11.5 Around Doors, Windows, and Other Openings
NOTE Door and window openings are common sources of acoustic flanking, and any cavity space adjacent to such openings that is left uninsulated short-circuits the acoustic performance of the surrounding partition. (11.5.1)
11.5.2 Insulation shall extend into all cavity space adjacent to door and window rough openings, around blocking for grab bars or backing, and into furred-out spaces at columns and other irregular conditions.
11.6 Plenum Insulation
11.6.1 Where the project requires plenum acoustic treatment above suspended ceilings, batt insulation shall be laid over the ceiling tiles on both sides of the partition for a width of at least 4 feet on each side, or extended fully across the room as indicated on the drawings.
11.6.2 Insulation laid over tiles shall be sized so it bears on the suspension grid rather than on the tile face, because insulation bearing on the face of a thin tile produces visible sag that the Owner will reject.
11.6.3 Batts shall be cut around recessed light fixtures and other in-plenum equipment to maintain manufacturer-required clearances.
11.6.4 Plenum Batt Width
4 ft each side (standard)
6 ft each side
Full ceiling area
Per drawings — plenum acoustic treatment plan
11.7 Floor and Ceiling Cavity Insulation
NOTE The IIC and STC performance of a floor/ceiling assembly is similarly sensitive to cavity-fill completeness. (11.7.1)
11.7.2 In wood- or steel-joisted floor/ceiling cavities, batts shall be installed friction-fit between joists and retained by wire support rods, plastic mesh, or strapping at 18 inches on center to prevent sag.
11.7.3 The full joist depth shall be filled where the assembly is intended to provide acoustic separation between floors.
11.7.4 Mechanical equipment, recessed lighting, and other in-cavity items shall be split around with the same care as in stud cavities.
12 Continuity and Perimeter Treatment
12.1 Top of Partition
NOTE The top of the partition is among the most frequently compromised conditions in acoustic and fire-rated work. (12.1.1)
12.1.2 Where the partition extends deck-to-deck, the insulation shall fill the cavity continuously from the floor runner to the deck above, without leaving an unfilled space at the head-of-wall joint.
12.1.3 Where the partition includes a deflection head detail, the insulation shall be cut to allow the slip track movement while still fully filling the cavity below the deflection range, or a compressible insulation shall be used at the head joint as specified by the tested assembly.
12.1.4 Where the partition terminates at the suspended ceiling, the cavity above the ceiling line shall be insulated, plenum-barriered, or both, as specified by the drawings.
NOTE A partition that terminates at the ceiling without plenum treatment provides only the limited acoustic separation that the suspended ceiling alone provides, typically much lower than the partition's nominal STC. (12.1.5)
12.2 Penetrations and Firestopping
NOTE Cavity-fill insulation, even fully installed, does not provide the rated stopping performance required at a penetration; the firestopping system is required in addition to the cavity insulation. (12.2.1)
12.2.2 Acoustic insulation is not a substitute for firestopping at penetrations through rated assemblies.
12.2.3 Penetrations — for conduit, piping, ductwork, cable trays, and other building services — shall be firestopped in accordance with Firestopping and with the rated penetration designs cited on the drawings. 12.2.4 ASTM C919 acoustic sealant shall be applied around all penetrations and at all perimeter conditions of acoustically rated partitions, coordinated with Gypsum Board Assemblies. 12.3 Acoustic Sealant Coordination
NOTE Acoustic insulation in the cavity provides no STC benefit if perimeter air paths around the gypsum board face leak sound around the assembly. (12.3.1)
NOTE Cavity-fill insulation and perimeter acoustic sealant are mutually dependent; either alone is insufficient. (12.3.2)
12.3.3 The Contractor shall coordinate insulation installation with the application of acoustic sealant at floor runners, top runners, perimeter conditions at adjacent walls and columns, and at all penetrations.
13 Coordination with Penetrations and Firestopping
NOTE Back-to-back electrical boxes are an acoustic flanking path that no amount of cavity insulation will mitigate. (13.1)
13.2 Where rated assemblies contain penetrations — for conduit, sleeves, pipe, ductwork, electrical boxes, and cable trays — the firestopping system at each penetration shall be selected from the applicable UL or GA-listed penetration firestop designs for the assembly.
13.3 Acoustic cavity-fill insulation shall be installed continuously up to and around the penetration, with care taken to avoid disturbing the firestop assembly.
13.4 The firestopping installer shall coordinate timing with the insulation installer; where firestop must be re-applied after cavity insulation is in place, the insulation shall be reinstated to its installed condition before the cavity is closed.
13.5 The gypsum-board specification (see Gypsum Board Assemblies) shall be enforced to require offset of back-to-back boxes by 24 inches minimum and the use of acoustic putty pads or listed acoustic box covers in high-STC partitions. 14 Mock-Ups
14.1 Where field testing is also specified, the mock-up may serve as the test specimen for field STC verification per ASTM E336 before production partition work proceeds, allowing any deficiencies to be corrected at a single representative location rather than across the entire project.
14.2 Where the project includes high-STC rated assemblies (STC 55 or higher), critical-listening rooms, or other acoustically demanding spaces, a mock-up of each rated partition type may be required by the contract documents.
14.3 The mock-up shall include the framing, cavity insulation as specified, both face layers of gypsum board, all accessories, and perimeter sealing, so that the complete assembly can be reviewed by the Architect and the acoustic consultant before production work begins.
14.4 Mock-Up Requirement
○ Yes — one mock-up per high-STC partition type (STC 55+)
○ Yes — one mock-up of each rated partition type
● No
15 Field Testing
15.1 STC Field Verification
NOTE Field acoustic testing per ASTM E336 measures the apparent sound transmission class (ASTC) or the noise isolation class (NIC) of an installed partition or assembly, accounting for flanking paths and construction variations that laboratory tests do not capture. (15.1.1)
NOTE Field-tested values typically run 3 to 5 STC points below the laboratory rating of the same assembly. (15.1.2)
15.1.3 Where field testing is specified, the acceptance criterion shall be expressed as a minimum field-measured ASTC or NIC, not as the laboratory STC value, because requiring the laboratory STC in the field is generally unachievable and creates dispute conditions.
15.1.4 Field Acoustic Testing and Acceptance
○ Yes — ASTM E336 measurement by independent accredited testing agency
○ Yes — owner-furnished testing
● No
Per drawings
ASTC ≥ STC – 5 (typical specification)
ASTC ≥ STC – 3 (tight specification, high-performance work)
NIC ≥ specified noise isolation class
Per drawings — acoustic acceptance criteria schedule
15.2 Testing Conditions
15.2.1 Field testing shall be performed by an independent accredited acoustic testing agency with experience in commercial construction field measurements.
15.2.2 Tests shall be conducted after all penetrations, perimeter sealing, doors, and adjacent finishes are complete; testing before finishes are complete will produce results that do not reflect final assembly performance and shall not be used as the basis for acceptance.
15.2.3 The testing agency shall provide a test report for each tested assembly including the source and receive room volumes, the measurement method (ASTM E336 procedure), the third-octave-band transmission loss data, the calculated ASTC or NIC, the acceptance criterion, the pass/fail determination, and any corrective action recommended for failed assemblies.
15.3 Corrective Action for Failed Tests
NOTE The most common causes of a failed field test are incomplete cavity fill, perimeter leakage, back-to-back electrical boxes, or door-frame leakage. (15.3.1)
15.3.2 Where a field-tested partition does not meet the acceptance criterion, the Contractor shall investigate the cause and shall implement corrective measures before re-test.
15.3.3 The Contractor shall not adjust the acceptance criterion or argue that the laboratory STC is satisfied by an inferior field measurement; the contract specifies the field performance and the field performance shall be achieved.
16 Delivery, Storage, and Handling
16.1 Acoustic insulation shall be delivered to the project in the manufacturer's original packaging with all labels and markings intact.
16.2 Bundles shall be stored indoors in a dry, climate-controlled location, off the ground on pallets or sleepers, and protected from rain, condensation, mechanical damage, and direct sun.
16.3 Plastic shipping wrap shall remain on bundles until they are brought to the point of installation; opened bundles shall be installed promptly or returned to enclosed storage.
16.4 Bundles that have been wetted shall be inspected.
16.5 Mineral wool products that have been briefly wetted may be dried and used if no fiber-matrix deformation is evident, but bundles showing crushing, compression set, or mold growth shall be rejected.
16.6 Glass fiber products that have been wetted shall be rejected, because the binder softens and the batt loses dimensional stability.
16.7 Insulation shall not be exposed to direct UV for prolonged periods, because the binder in some glass fiber products is UV-sensitive.
16.8 Temporary storage outdoors under tarp is acceptable only for short durations and only with full protection from precipitation; long-term outdoor storage shall not be used.
17 Warranty
17.1 Manufacturer's Warranty
17.1.1 Acoustic insulation products shall be warranted by the manufacturer against defects in materials and workmanship for a minimum period of one year from the date of delivery.
17.1.2 Mineral wool board products and engineered acoustic batts carrying extended manufacturer warranties shall be warranted for the period stated by the manufacturer.
17.2 Installer's Warranty
NOTE Workmanship defects include, but are not limited to, missing cavity fill, sagged or settled batts, compressed batts in undersized cavities, and unfilled spaces around blocking, boxes, or penetrations that compromise the rated performance of the assembly. (17.2.1)
17.2.2 The Contractor shall warrant the acoustic insulation installation — including cavity fill completeness, retention, and integration with the host assembly — against defective workmanship for the project warranty period.
17.2.3 Installation Warranty Period
1 year from substantial completion
2 years from substantial completion
17.3 Conditions Voiding Warranty
17.3.1 The warranty is voided by subsequent water intrusion, modifications by others that disturb the cavity insulation, and removal or alteration of insulation during post-occupancy work that is not restored to the installed condition.
17.3.2 The Contractor shall document any conditions observed during installation that may affect the long-term performance of the insulation — evidence of water infiltration, inadequate climate control, or trades disturbing previously installed cavity insulation — and shall bring them to the Architect's attention before the cavity is closed.