ASTM E90

Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements

Last updated: April 28, 2026

Overview

ASTM E90 is the laboratory test method that measures how much sound a wall, floor, ceiling, door, or other building element blocks. It is the foundational acoustical test in North American construction. When a manufacturer publishes a sound transmission rating for a partition, door, or seal, that rating almost always traces back to a test run per ASTM E90.

E90 by itself produces transmission loss data at 18 frequency bands. That raw data is then converted into a single-number rating, the Sound Transmission Class or STC, using ASTM E413. The two standards travel together: a product specification that calls for an STC rating is implicitly calling for an E90 test. You will see the pair written as "tested per ASTM E90, rated per ASTM E413."

Why E90 matters on this site: products that affect building acoustics carry the ASTM-E90 tag. That includes door bottoms, smoke seals, perimeter seals, acoustical sealants, and firestop sealants that double as sound-blocking products. The compliance signal is real, but it only helps the buyer if the buyer knows what STC means and what numbers to ask for.

E90 measures only airborne sound. Footsteps, dropped objects, and other structure-borne impact sound are measured by ASTM E492 in the lab and rated as IIC (Impact Insulation Class) per ASTM E989. A floor or ceiling assembly typically needs both: an STC rating from E90 plus an IIC rating from E492. Specifying only STC on a multi-family floor can pass the airborne requirement and still produce noise complaints from foot traffic above.

For door assemblies that combine fire, smoke, and acoustic performance, see UL 1784 (smoke leakage) and UL 10C. For sealant chemistry behind acoustical caulks and firestop products that carry an STC rating, see ASTM C920.

What ASTM E90 Measures

The test specimen separates two reverberation chambers. One chamber is the source room, the other is the receiving room. Loudspeakers in the source room generate a calibrated, broadband noise field. Microphones sample the sound pressure level in both rooms.

Transmission loss at each frequency is the difference between the source-room sound pressure level and the receiving-room sound pressure level, corrected for the receiving-room absorption. The standard requires measurements across 18 one-third-octave bands from 125 Hz through 4000 Hz.

Test conditions specified by E90

Specimen mounted in a filler wall between two reverberation chambers, fully sealed at the perimeter
Source-room sound field calibrated to be diffuse (uniform across the room volume)
Receiving-room absorption measured separately so the result reflects the specimen, not the chamber
Flanking paths around the specimen verified to be at least 10 dB below transmission through the specimen
Reported result: 18 transmission loss values, one per one-third-octave band from 125 Hz to 4000 Hz

The 18 numbers do not communicate well to architects, building owners, or contractors. That is the job of E413, which condenses them into a single STC value.

STC: The Single-Number Rating

ASTM E413 takes the 18 transmission loss values from an E90 test and fits them against a reference contour. The contour is a curve shaped roughly like the speech-audibility region of human hearing. STC is the value of the contour at 500 Hz once the curve has been shifted as high as possible against the data, subject to two limit rules.

The two STC fitting rules

No single one-third-octave band may fall more than 8 dB below the contour
The cumulative deficiency (sum of every band below the contour) may not exceed 32 dB

Higher STC means more sound blocked. A 5-point STC change is roughly perceptible to occupants. A 10-point change feels like a clearly different room.

STC is weighted toward speech, not bass. The contour starts at 125 Hz and emphasizes the 250 Hz to 2500 Hz speech range. A wall with high STC can still feel thin against music with strong bass, theater subwoofers, or low-frequency mechanical noise. For traffic noise, theaters, and rooftop mechanical equipment, OITC (covered below) is the better single-number metric.

Typical STC by Assembly

These values are representative of well-built assemblies in published lab catalogs. Real STC depends on construction details (insulation, stud type, fastening, sealing), so verify with the manufacturer or assembly catalog before specifying.

Assembly	Typical STC
Single-leaf 5/8" gypsum on wood studs, no insulation	33 to 35
Double-leaf gypsum (5/8" each side) on wood studs, no insulation	37 to 40
Double-leaf gypsum on wood studs with batt insulation	40 to 45
Staggered or double wood-stud wall with insulation	50 to 55
Double-leaf gypsum on resilient channel with insulation	50 to 55
8" concrete masonry unit (CMU), painted	50 to 52
6" reinforced concrete slab	52 to 55
Solid-core wood door with quality perimeter and bottom seals	30 to 35
Hollow-metal door with smoke seals	25 to 30
Acoustical door assembly (gasketed, full perimeter seal)	40 to 50

The door is usually the weak link. A wall rated STC 50 is meaningless if the door in it rates STC 25. Composite STC of a wall with a door is dominated by the lowest-rated component weighted by area. On multi-family corridors, healthcare patient rooms, and hotel guest rooms, the door perimeter and bottom seals are the deciding factor. Spec the seals.

IBC and Code References

Most acoustical compliance language in US building codes references E90 by way of STC. The most common requirements live in residential occupancy chapters and in healthcare, hospitality, and education guidance.

IBC Section 1206 (Sound Transmission)

The International Building Code requires walls, partitions, and floor or ceiling assemblies separating dwelling units from each other and from public spaces (corridors, stairs, mechanical rooms) in Group R occupancies to meet a minimum STC of 50 in the lab. Field-tested rating, expressed as NIC (Noise Isolation Class), must reach at least 45.

Lab requirement: STC 50 minimum for separating walls and floor or ceiling assemblies (per ASTM E90 / E413)
Field requirement: NIC 45 minimum (per ASTM E336)
Floor or ceiling assemblies between dwelling units also require IIC 50 lab / 45 field for impact noise (per ASTM E492 / E989)
Penetrations and joints in rated separations must maintain the rating (sealants and seals come into play here)

E90 vs OITC vs IIC

Three single-number ratings show up in acoustical specs. They are not interchangeable.

Rating	Source Test	What It Measures	When To Use It
STC	E90 lab test, E413 rating	Airborne sound, speech-weighted	Most interior partitions, doors, demising walls
OITC	E90 lab test, E1332 rating	Airborne sound, low-frequency-weighted	Exterior walls, windows, roof assemblies near traffic or aircraft
IIC	E492 lab test, E989 rating	Impact (footstep) sound through floors	Floor and ceiling assemblies in multi-family

Same E90 lab data can produce both an STC and an OITC, because OITC is just a different weighting of the same transmission loss curve. The OITC contour extends down to 80 Hz and weights low frequencies more heavily, which is why OITC ratings are usually 5 to 10 points lower than STC for the same assembly. For an exterior wall against highway traffic, the OITC is the more honest number.

Lab vs Field Ratings

A wall that tests STC 55 in the lab almost always rates lower in a real building. Field conditions add flanking paths, imperfect seals, electrical and plumbing penetrations, and mechanical openings the lab specimen never had. The industry uses different acronyms for lab and field ratings to keep the distinction clear.

Rating	Test Standard	Where Measured
STC	ASTM E90 / E413	Laboratory only, idealized chamber
FSTC	ASTM E336 / E413	Field, partition only (flanking corrected out)
NIC	ASTM E336	Field, total isolation between rooms (flanking included)
ASTC	ASTM E336	Field, apparent rating (older term, similar to NIC)

Rule of thumb: NIC in the field typically lands 5 points below the lab STC of the partition. IBC anticipates this gap by setting field NIC at 45 against a lab STC of 50. The 5-point margin is consumed by penetrations, gaps under doors, gaps around outlets, and flanking through shared structure. Sealing penetrations and specifying perimeter and bottom seals on doors is how that margin gets preserved.

Doors, Seals, and Sealants

Most products on this site that carry the ASTM-E90 tag are not walls. They are door bottoms, smoke and acoustical seals, perimeter gasketing, and acoustical or firestop sealants. The reason is structural: a door or a penetration is the leak path that decides whether a partition meets its rated STC in the field.

Door perimeter and bottom seals

A solid-core wood door rated STC 32 will field-rate closer to STC 22 if the perimeter has 1/8" gaps and there is no bottom seal. Door manufacturers and seal manufacturers (Pemko, NGP, Reese) publish tested STC values for door plus seal combinations. The seal is part of the rated assembly. Specifying the door alone is not enough.

Automatic door bottoms drop a flexible seal when the door closes, sealing the threshold gap
Mortised perimeter seals fit into a routed kerf in the door edge or frame
Surface-applied perimeter gaskets fasten to the stop face
Smoke seals (UL 1784) often serve double duty as acoustical seals; both depend on continuous perimeter contact

Acoustical and firestop sealants

Where partitions terminate at structure, run past slab edges, or get penetrated by pipes and conduit, the joint or penetration is sealed. Whether the sealant is a dedicated acoustical product (sound-rated, non-hardening) or an intumescent firestop sealant, the manufacturer typically reports an STC value for a tested wall assembly using that sealant. The ASTM-E90 tag on these products signals that the manufacturer has lab data backing the combined assembly rating.

For sealant chemistry and joint design behind these products, see the 2025 Sealant and Caulking Selection Guide. For door hardware sequencing, see the Fire Door Gasketing Guide and the Door Closer Selection Guide.

Verifying a published STC: ask the manufacturer for the tested assembly description, the test report number, and the testing laboratory. A published STC without a tested assembly is a marketing claim, not a spec.

Frequently Asked Questions

Is ASTM E90 the same thing as STC?

No. ASTM E90 is the lab test method that measures airborne sound transmission loss across 18 frequency bands. STC is the single-number rating derived from that data per ASTM E413. You need both: the test (E90) generates the data, and the rating method (E413) compresses it into the STC value that gets written into specs.

What STC do I need for a multi-family party wall?

IBC Section 1206 sets a minimum lab STC of 50 for walls separating dwelling units, with field NIC of 45. That is a floor, not a target. Many developers and acoustical consultants spec STC 55 in the lab to land at NIC 50 in the field, which audibly outperforms code minimum. Hotels and condos often go to STC 60 for premium guest experience.

Why is the field rating lower than the lab rating?

Lab specimens have no flanking paths and perfect perimeter seals. Real buildings have shared studs, continuous floor decks, ductwork, electrical back-to-back outlets, and gaps at door bottoms. Each of these leaks sound around the rated partition. NIC field rating typically falls 5 points below the lab STC for that reason. Sealing penetrations preserves most of the margin. Sloppy work loses 10 points or more.

Does a higher STC always mean a quieter room?

For speech, yes. For low-frequency noise (traffic, theater bass, mechanical equipment, footsteps), STC can be misleading because the rating contour starts at 125 Hz and weights mid frequencies. A wall rated STC 55 can still let bass through. For exterior walls and windows near traffic, OITC is a better metric. For floor or ceiling assemblies, IIC is the rating that catches footstep noise.

How does a door seal affect STC?

A 1/4" gap under a door can drop the assembly rating by 10 to 15 STC points regardless of how heavy the door is. Gaps act as direct sound paths. Adding an automatic door bottom and continuous perimeter seals brings the assembly back toward the door's tested rating. Door manufacturers publish STC values for the door plus a specific seal package; substituting seals voids that tested rating.

Can a firestop sealant also be acoustical?

Yes. Many intumescent firestop sealants and putties are tested in wall assemblies under E90 and report an STC value alongside their UL 1479 fire rating. The same continuous, flexible bead that blocks fire and smoke also blocks airborne sound. On a rated demising wall with electrical penetrations, one product can satisfy both fire and acoustic requirements when the listed assembly supports it.