What is the STC rating of spray foam? | ASLONG Guide

What is the STC Rating of Spray Foam?

Professionals in the sound insulation industry frequently seek reliable information about the STC rating of spray foam, a key factor in sound control. This article provides authoritative, concise insights into how spray foam insulation performs acoustically and what industry experts need to know.

Understanding STC Ratings

- Definition: STC stands for Sound Transmission Class, a standardized rating to measure how effectively a building material attenuates airborne sound.

- Scale: STC values typically range from 20 (poor) to 60+ (excellent), according to ASTM E413-10 standards. (Source: ASTM International)

- Interpretation: Higher STC = better sound blocking.

Spray Foam Insulation: Types & Acoustic Performance

- Types:

- *Open-cell spray foam*: Lower density, softer structure, more effective at absorbing mid-to-high frequencies.

- *Closed-cell spray foam*: Higher density, greater rigidity, improved thermal insulation, but relatively less effective for airborne noise.

- Typical STC Ratings:

- *Open-cell spray foam in a standard wall assembly*: STC 37–39.

- *Closed-cell spray foam in the same assembly*: STC 36–38.

- Baseline comparison: Standard 2x4 timber stud wall with no insulation typically achieves STC 33–35.

Factors Impacting STC Ratings of Spray Foam

- Wall Facings: The STC of a wall system depends on drywall thickness, number of layers, and overall assembly.

- Application Thickness: Thicker spray foam layers tend to perform better acoustically but returns diminish after standard wall thicknesses.

- Installation Quality: Gaps or voids can reduce the effective STC rating.

Performance Data and Industry Guidance

- Lab-Certified Results:

- According to National Research Council Canada data, open-cell spray foam assemblies can exceed STC 40 when installed with double drywall and resilient channels.

- Limitations:

- Spray foam, even at its best, does not match specialized soundproofing materials like mass-loaded vinyl (MLV) or decoupled double-wall systems, which can achieve STCs above 50.

- Best Practices:

- For projects with critical sound insulation needs, combine spray foam with additional sound-dampening treatments.

Pros & Cons of Spray Foam for Sound Insulation

- Pros:

- Effective for mid-range sound dampening.

- Provides combined thermal and moderate acoustic performance.

- Expands to seal cracks and gaps, minimizing flanking noise.

- Cons:

- Less effective than heavy or decoupled assemblies for low-frequency and impact noise.

- Primary benefit is air sealing and thermal insulation; STC boost is relatively modest.

Key Takeaways for Sound Insulation Professionals

- Spray foam alone usually delivers an STC rating in the 36–39 range in standard walls.

- Enhance performance with double drywall, acoustic sealants, and resilient channels.

- Always refer to assembly-specific, lab-tested STC data for project planning.

- (Authoritative Source: National Research Council Canada, ASTM International)

For precise STC ratings, consult manufacturer datasheets and ASTM E90-certified test reports.

*ASLONG: Your expert partner in sound insulation materials and solutions.*