How to Achieve ASTM E90 Certification

By James Hartley · May 1, 2026

1) Project overview: what, where, who, and why

In late 2024, Sonus Gear Flow was asked to document and support a sound isolation verification program for a tenant-improvement project inside a mixed-use building in Somerville, Massachusetts. The client was a boutique post-production studio called Northline Edit, moving into a 3,800 sq ft second-floor suite above a ground-floor café and adjacent to a co-working space. Their lease required formal third-party test documentation demonstrating that their two critical rooms—the mix room and the VO booth—met an airborne sound isolation target equivalent to STC 60 for the demising wall and STC 55 for the corridor wall.

Because the studio planned to market the rooms to outside clients, they wanted the validation to be more than “we built it like an STC 60 wall.” They specifically requested testing aligned with ASTM E90 (Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements). The twist: the project wasn’t in a laboratory. We addressed this by executing a field test program using ASTM E336 for in-situ measurements, while designing and documenting the construction to match an ASTM E90 laboratory-rated assembly. The deliverable was a certification package commonly requested by landlords and insurers: (1) assembly documentation referencing E90 lab data from a recognized lab report, plus (2) on-site verification data demonstrating the installed construction met the isolation objective when measured in the field.

The core team included Northline’s project manager, the GC (a small commercial contractor), the architect, a mechanical subcontractor, and Sonus Gear Flow providing acoustic consulting and test coordination. Third-party measurements were performed by an independent acoustical test agency using calibrated instrumentation and traceable records.

2) Challenges and requirements at the outset

Three constraints defined the project before a single stud was ordered:

Limited floor-to-floor height: The existing structure provided 10 ft 2 in slab-to-slab. After duct routing and lighting coordination, the ceiling cavity available for a decoupled assembly was tighter than typical studio builds.
Flanking risk: The demising wall between the mix room and co-working space ran continuously to the exterior wall, and the building had a steel beam line that could easily couple vibration if the wall was hard-tied.
Schedule and noise constraints: The café below operated from 7 a.m. to 3 p.m. The building prohibited high-noise construction after 6 p.m., which affected both build sequencing and when we could perform acoustic testing with sufficient dynamic range.

The performance requirement was not stated as “transmission loss at each third-octave band,” but as an STC target. For certification purposes, we needed to show the installed wall behaved consistently with an assembly that has recognized lab-tested performance per ASTM E90. The project manager also wanted a predictable path to pass/fail without expensive rework, so we baked measurement checkpoints into the schedule.

3) Approach and methodology chosen

We used a two-pronged method:

Design to a known ASTM E90-tested assembly: We selected a demising partition configuration with a published E90 lab report indicating STC 60+ under controlled conditions, then documented the build in a way that could be compared line-by-line to that lab assembly (stud gauge, spacing, insulation density, gypsum type and thickness, screw patterns, sealant, and penetrations).
Verify the installation with ASTM E336 field testing: Field conditions rarely match the lab. So we planned a test after drywall, sealing, and doors were installed but before final finishes locked us out of access. We targeted field results consistent with FSTC 55–58 for the demising wall, understanding that field numbers often come in 3–10 points below lab STC because of flanking and workmanship variability.

For equipment, the test agency specified a dodecahedron source capable of high output and predictable directivity, a measurement mic with recent calibration, and analysis software supporting third-octave band processing and STC calculation. They used a NTi Audio DS3 dodecahedron speaker driven by an NTi PA3 power amplifier, and measurement via an NTi XL2 analyzer with a Class 1 mic. Sound level checks were cross-verified with a Brüel & Kjær 2250 brought by the agency lead for redundancy.

4) Step-by-step execution narrative

Week 1–2: Preconstruction documentation and risk mapping

We started with a 90-minute kickoff onsite. Instead of discussing “STC walls” in general, we walked the perimeter of the planned mix room and identified every likely flanking path: slab edge, beam pockets, façade mullions, existing pipe penetrations, and the shared plenum above the corridor. We then produced a one-page “isolation risk map” for the GC. This became the reference during framing and MEP rough-in.

We also issued a submittal package listing acceptable equivalent materials. The owner preferred a specific gypsum brand for supply reasons, so we pre-approved alternates that matched density and Type X requirements. This prevented last-minute substitutions that can derail performance.

Week 3–5: Framing and decoupling details

The demising wall assembly was built as a double-stud wall with a 1 in air gap. Each stud line used 3-5/8 in 20 ga metal studs at 24 in o.c. on separate tracks. The key instruction to the framing crew was simple: no bridging between frames—no shared top track, no scraps used as “stiffeners,” and no electrical boxes spanning the cavity.

At the slab and underside of structure, we used a continuous bead of non-hardening acoustical sealant under tracks. The GC wanted to use standard construction adhesive at first, but we rejected it because it cures rigid and can create unintended mechanical coupling. We specified OSI SC-175 (or equivalent) for its long-term flexibility.

Week 6: Insulation and pre-drywall inspection

Insulation was 3-1/2 in mineral wool (nominal 2.5 lb/ft³) in each stud cavity. We didn’t overpack; we insisted on full depth without compression. Overstuffed batts can bow gypsum and create fastener gaps that leak sound.

Before drywall, we performed a “flashlight inspection” for air paths. With the lights off, a bright LED light was placed on one side of the wall while observers on the other side checked for light leaks at slab edges, track discontinuities, and around preinstalled sleeves. We found two problem zones: a 3/8 in gap at the beam web and a poorly cut sleeve around a condensate line. Both were sealed before board went up.

Week 7–8: Drywall layering, damping, and airtightness

For the demising wall, each side received two layers of 5/8 in Type X gypsum. The first layer was installed vertically with screws per manufacturer recommendations. The second layer was offset so seams did not align. Between layers, we used a constrained-layer damping compound at a controlled application rate—approximately 2 tubes per 4x8 sheet—to improve mid-band transmission loss. We documented batch numbers and coverage rates because “we used Green Glue” is not the same as proving consistent application.

At the perimeter of each layer, we left a 1/4 in gap to avoid hard contact to slab and columns, then filled it with acoustical sealant. The GC initially wanted to tape and mud the corners flush to the slab; we required the resilient gap remain and be sealed, not bridged with rigid compound.

Week 9: Doors, glazing, and penetrations

The corridor wall required STC 55-class performance, but the biggest failure point is almost always the door set. For the mix room entry, we selected a 1-3/4 in solid-core door, 20-minute rated, with full perimeter compression seals and an automatic drop seal. Hardware included a cam-lift hinge to improve consistent latch-side compression. We avoided dual doors due to space and egress constraints, but we did specify a heavier leaf (approx. 110 lb) and reinforced frame anchoring.

All electrical boxes in the demising wall were prohibited. For the corridor wall, any boxes were installed in surface raceway inside the room rather than recessed in the partition. HVAC penetrations were routed through lined flex with at least two bends and a lined plenum box to avoid a straight-line sound path.

Week 10: Pre-test commissioning and background noise management

Two days before the test, we conducted a quick internal check using a portable source and measurement mic—not to “predict STC,” but to identify gross leaks. We played pink noise at moderate level and walked the receiving side with a handheld SPL meter, listening for localized hiss indicative of air gaps. A consistent leak showed up at the door undercut where the drop seal hadn’t been adjusted. That adjustment alone typically changes real-world isolation more than adding another layer of drywall.

To ensure sufficient test dynamic range, we scheduled official testing from 6:30 a.m. to 9:30 a.m. before the café ramped up. The building’s base HVAC was kept on (as required by the standard for realistic conditions), but we temporarily disabled the studio’s internal supply fan during measurements to reduce receiving room noise floor.

5) Technical decisions and trade-offs made

Double-stud vs. clips and channel: Clips and hat channel would have preserved floor area, but the steel beam line and framing crew familiarity pushed us toward double-stud for predictable decoupling. The trade-off was losing about 9 in of width at the demising line compared to a single stud with resilient channel.
Damping compound vs. additional mass: A third layer of gypsum would have increased low-frequency isolation but exceeded weight and schedule constraints. Damping improved performance in the speech and mid bands where the studio’s isolation requirement was most critical for neighbor comfort.
No recessed boxes: This complicated electrical routing and increased conduit runs, but it removed a common weak point that can erase 5–10 STC points in practice if back-to-back boxes occur.
Field test expectation management: We aligned stakeholders early that “ASTM E90 certification” would be met through assembly traceability plus field verification. If a lease demanded a lab-only E90 test, the only honest path would be constructing a representative wall specimen and sending it to a lab—typically a 6–10 week lead time and substantially higher cost.

6) Results and outcomes with specific details

Testing was performed in accordance with ASTM E336 procedures, with third-octave band measurements from 125 Hz to 4000 Hz, room averaging across multiple mic positions, and correction for background noise. The source room level was maintained high enough to achieve at least a 45 dB level difference above the receiving room noise floor in most bands.

Demising wall (mix room to co-working space): The final calculated result was FSTC 57. The measured transmission loss curve tracked the expected mid-band performance closely, with the largest weakness observed in the 125–160 Hz region—consistent with flanking through structure and the reality of field conditions.

Corridor wall and door (mix room to corridor): The wall alone tested stronger, but the assembled system including the door set produced FSTC 51 on the first pass, which did not meet the project’s practical expectation for privacy. The analysis pointed to door leakage rather than wall deficiency: strong high-frequency transmission and a signature consistent with perimeter gaps.

We paused final sign-off and executed corrective actions within 48 hours:

Adjusted the automatic drop seal to achieve uniform contact across the sill.
Re-shimmed the frame to correct a slight twist at the latch corner (measured ~3/32 in gap under compression).
Replaced one section of perimeter seal that had been cut short at the header.

On the re-test, the corridor assembly improved to FSTC 54. While still below the lab-rated wall value, it achieved the client’s functional goal: intelligible speech from the corridor was reduced to a murmur, and typical session playback at 83 dB SPL (C-weighted) inside the mix room did not generate complaints during normal co-working hours.

Timeline-wise, the acoustic scope from kickoff to final field report took 11 weeks. The independent test agency delivered the stamped report within 5 business days of the final measurement session. The total cost attributable to acoustic detailing and testing (consulting time, documentation, and two field test visits) landed at roughly $14,800, excluding construction materials.

7) Lessons learned and what could be done differently

The project succeeded, but two items are worth calling out as “next time, do it earlier” improvements:

Door set commissioning should happen before paint: We caught the leakage in time, but adjusting seals after paint increases the risk of cosmetic damage and slows down turnover. A door “air-leak check” should be scheduled immediately after hanging hardware and before finish work.
Plan test windows around building occupancy: Even early morning testing had moments where delivery trucks and café prep raised the receiving room noise floor. In future mixed-use buildings, we would request a building notice to reduce adjacent activity for a two-hour window, or test on a Sunday if permitted.

We also would have benefited from adding a small accelerometer-based check on suspected structural flanking points. While not required for certification, vibration measurements can help explain low-frequency anomalies and guide whether additional isolation (floating floor, isolated ceiling) is justified.

8) Takeaways applicable to other projects

“ASTM E90 certification” is a documentation strategy, not a single checkbox: In most commercial build-outs, you combine a wall assembly that has an ASTM E90 lab report with rigorous installation documentation and then verify in the field using ASTM E336. Be clear with stakeholders which test applies to which claim.
Airtightness is the cheapest STC you’ll ever buy: The flashlight inspection, perimeter sealant, and door seal tuning produced more practical benefit than any last-minute mass addition would have.
Control substitutions: Track gauge, stud spacing, gypsum type, and insulation density all matter. If the assembly deviates from the lab-tested version, your “E90-backed” claim gets weaker fast.
Design around the door from day one: If you need corridor privacy, budget for a heavy door leaf, real seals, and installation time. A high-performing wall with a leaky door will fail client expectations every time.
Build in a measurement checkpoint: Testing after drywall and doors—but before finals—keeps rework affordable. Treat the test as commissioning, not a postmortem.

For audio engineers and project managers, the core lesson is that certification-grade outcomes come from making sound isolation measurable and repeatable: pick an assembly with known lab performance, build it without “small” deviations, and verify the installed result with field-appropriate standards. When the inevitable gap or flanking path shows up, you’ll have the data and access needed to fix it quickly—and you’ll end up with documentation that holds up under landlord scrutiny and client expectations.