What does an OITC rating mean, and how should it be used when evaluating windows, walls and building façades? This guide explains Outdoor-Indoor Transmission Class (OITC), the limitations of rating charts, and the distinction between laboratory product data and measurements of installed construction.
What Is OITC?
Outdoor-Indoor Transmission Class (OITC) is a single-number acoustical rating calculated using ASTM E1332. It is intended to characterize the ability of a building assembly to attenuate outdoor noise, with a frequency weighting relevant to transportation noise. OITC is not the same as STC: the ratings use different frequency ranges and weighting methods, so their numerical values should not be directly compared.
How to Read an OITC Rating Chart
OITC rating charts often list values for windows, glazing systems, exterior doors and wall assemblies. In general, a higher OITC rating represents greater sound attenuation under the defined rating method. However, a chart is only meaningful when the reader knows the tested assembly, whether the data are from a laboratory or the field, and which rating procedure was used.
- Check the test basis. Is the rating from a laboratory specimen, or was it derived from field measurements?
- Compare like assemblies. Glass thickness alone does not describe the complete window, frame, seals or installed wall.
- Check the frequency spectrum. Two assemblies with similar single-number ratings can perform differently at particular frequencies.
- Consider the installation. Air leakage, penetrations, adjoining construction and flanking paths can limit completed-building performance.
- Match the metric to the project. Field geometry and measurement conditions may call for FOITC, AOITC or OINIC rather than a laboratory OITC rating.
OITC vs. STC: Which Rating Matters?
STC is commonly used to characterize airborne sound isolation of building partitions, while OITC is designed for outdoor-to-indoor sound transmission. For a façade exposed to roadway, aircraft or other outdoor noise, OITC-related information can be particularly useful. Neither single-number rating replaces a frequency-specific assessment when the noise source has unusual tonal or low-frequency content. For installed interior partitions, see STC and ASTC field testing.
Laboratory OITC vs. Field Façade Testing
A manufacturer’s published laboratory OITC rating describes the tested specimen under controlled conditions. It does not establish the sound attenuation of an entire installed façade. ASTM E966 provides field procedures for evaluating outdoor-to-indoor attenuation of installed exterior walls, windows, doors and façade systems. Depending on the test method and site conditions, appropriate field ratings can include FOITC, AOITC or OINIC. These terms are not interchangeable. See ASTM E966 façade, window and door acoustic testing for the measurement methods OSAT offers.
Why We Do Not Publish a Generic OITC Performance Table
A table of purported OITC values without identified test reports, assembly details and rating methods can be misleading. OSAT instead recommends evaluating traceable laboratory data for the proposed assembly and measuring installed performance when project acceptance, complaints or diagnostic investigation require it.
When to Commission Field Testing
Field measurements are useful when hotel rooms, offices, residences or other spaces experience excessive exterior noise; when installed glazing or façade construction must be verified; or when completed work does not meet a project requirement. OSAT performs independent field testing, diagnostic investigation and retesting, rather than selling or installing window and wall products.
Explore commercial acoustics testing or all OSAT acoustic testing services. To discuss a façade test, provide the project location, building elevations, assembly descriptions, noise source and applicable criteria.
