Window sound requirements, by project.

The model building codes say nothing about noise coming through an exterior window. The IBC's STC 50 is for the wall between two apartments. So when a project carries a window sound requirement, it came from somewhere else: a city environmental review, a federal funding source, an airport program, a state code, a rating system, or the project's own acoustic consultant. Each one writes the number differently. This guide goes through them, then shows which of our tested glasses clears each one.

Two ratings, one lab test.

Both ratings come from the same laboratory measurement, ASTM E90: a window is built into a wall between two rooms and the sound loss is measured band by band.

• STC (ASTM E413) turns that curve into one number weighted for speech. ASTM's own text says it is not appropriate for traffic, aircraft or train noise.
• OITC (ASTM E1332) weights the same curve for the low rumble of transportation noise, and reads down to 80 Hz. It is the rating made for facades.

OITC runs lower than STC on the same window, usually by three to eight points, which is why a specification often pairs them: STC 40 / OITC 30.

One more distinction matters more than either rating: glass is not a window. A glass maker's STC is for the insulating unit alone. The whole window, with its frame, sash and seals, tests lower. New York's reviewers deduct 5 dB from any glass-only number, and then ask for a laboratory report on the actual window before it is bought. Ask every supplier for the whole-window report. Ours are below.

New York City: the noise (E) designation.

When a rezoning or a project goes through environmental review (CEQR) and the site is loud, the lot gets an (E) designation for noise. The Department of Buildings will not issue a permit, or a certificate of occupancy, until the Office of Environmental Remediation (OER) signs off. Replacing the windows on an (E) lot triggers the same review.

The requirement is written as window/wall attenuation, in dBA, for the window and the wall together. The CEQR Technical Manual sets four tiers from the measured street noise:

Above 80 dBA the requirement is the outside level minus the design level inside. The design level is 45 dBA inside for traffic noise and 40 dBA for aircraft and trains. Offices and meeting rooms get 5 dBA less in each tier.

Three things follow from the manual's wording:

1. The rating is OITC. The city's rule defines window/wall attenuation as based on the OITC of each facade component under ASTM E1332. STC is used only where a federal funding source requires it.
2. The windows are assumed closed. Every tier is a closed-window condition, so above 70 dBA outside the building needs an alternate means of ventilation: a device that brings in outside air so the operable windows can stay shut all year. Trickle vents and energy-recovery ventilators are the usual answers, and the mechanical engineer names them in a letter.
3. The number is composite. The acoustic consultant works out the window's OITC from the tier and the window-to-wall ratio of each facade. The street side and the courtyard side rarely need the same glass.

The process is a Remedial Action Plan certified by a New York architect or engineer, a Notice to Proceed from OER, the installation, then an Installation Report certified by the architect or engineer that what was approved went in, and a Notice of Satisfaction. OER's decision documents carry a table for the windows: facade, floors, the required OITC, how it is certified, the manufacturer and model, and the glazing. Where a supplier has no ASTM E90 test on file for the window assembly, OER requires a mock-up to be lab tested first. The window supplier's part is simple: a laboratory report for the whole window, rated to OITC, before purchase.

HUD-funded housing, anywhere.

Housing with HUD money follows HUD's noise regulation, 24 CFR Part 51, wherever it is built.

• A site at or below 65 dB DNL is acceptable.
• 65 to 75 dB is "normally unacceptable" and needs extra attenuation: 5 dB more than common construction from 65 to 70, 10 dB more from 70 to 75.
• Above 75 dB is unacceptable.
• HUD's interior goal is 45 dB DNL.

HUD works in STC, through its Sound Transmission Classification Assessment Tool. HUD's own guidance puts common construction at about 20 dB, so the targets come out to STC 25 for 65 to 70 dB sites and STC 30 for 70 to 75. A site at 80 dB would be looked at around STC 38. When a New York project has HUD funding, the CEQR review uses HUD's STC method instead of OITC.

Near an airport.

The FAA's sound insulation guidance (Advisory Circular 150/5000-9B) covers homes inside the 65 DNL contour. A home qualifies when it is at 45 dB or more inside with the windows closed; the program's goal is below 45 dB inside and at least a 5 dB improvement. The FAA does not fix one window rating; each airport's program does:

• Sea-Tac: the Port of Seattle states that these programs must use windows rated STC 44 or OITC 32.
• Reno-Tahoe: replacement windows STC 40 minimum (storm windows STC 30, secondary glazing STC 39).
• Los Angeles: no fixed window number; the goal is the interior level and the 5 dB improvement.
• City of SeaTac building code: for 25, 30 and 35 dB of required noise reduction, windows of at least STC 28, 33 and 36.
• Portland, Oregon: inside the airport overlay, an acoustical engineer certifies the building will reach 45 dBA DNL inside.
• Minneapolis-St. Paul: new homes in the airport zones are built to 45 dBA inside, under state statute.

California.

The California Building Code (§1206.4) caps noise from outside at 45 dB (Ldn or CNEL) in any habitable room, which covers multifamily. CALGreen (§5.507.4) adds a prescriptive path for nonresidential buildings inside a 65 dB contour of an airport, freeway, railroad or industrial source: walls at composite STC 50 or OITC 40, and exterior windows of at least STC 40 or OITC 30.

Rating systems.

• LEED v4.1 for Schools: exterior windows of at least STC 35, unless the measured outdoor and indoor levels justify less. LEED's New Construction acoustic credit has no exterior window number.
• WELL, Sound barriers: for multifamily buildings within half a mile of a major noise source, exterior windows, doors and openings of at least STC 35.

Everywhere else.

With no review, no HUD money, no airport and no state code, the number is the acoustic consultant's. A 2025 report for a site beside I-93 in Massachusetts, for example, asked for windows of OITC 26, or STC 35 where a supplier lists only STC. Whatever the number, ask for it three ways: as OITC with STC beside it, for the whole window, and per facade.

Our four glasses, against each requirement.

Every Vistaza sound rating is a whole-window laboratory test to ASTM E90 by Intertek, on a Vi6 casement. The frame stays the same; the glass changes. There is no framing-loss correction to apply, because the frame was in the test.

For an (E) site, send us the (E) number and the elevations. We return the glass per facade and the Intertek report for the OER table. Where the project uses trickle vents for its alternate means of ventilation, the same window passed its water test with the vent in and with it out.

What we send with the windows.

• The Intertek sound report for the window as tested, with the STC and the OITC.
• The glass by elevation on the window schedule.
• The NFRC certificate for the same glass, so the energy number is settled at the same time.