Side-by-Side Comparison
Thermal Insulation & Acoustics
Thermal Insulation R-Values vs. Sound Transmission Class (STC) Ratings
Comparing 2 standards across 14 specifications. 14 key differences identified.
Comparing:
Thermal Insulation R-Values
Sound Transmission Class (STC) Ratings
Thermal insulation materials are standardized under ASTM C518 and the International Energy Conservation Code (IECC) by their thermal resistance (R-value per inch of thickness, hr·ft²·°F/Btu / RSI in m²·K/W), ranging from fiberglass batts (R-3.1/in) to polyisocyanurate and closed-cell spray foam (R-6.5 to R-7.0/in).
Sound Transmission Class (STC) is an integer rating standardized under ASTM E90 and ASTM E413 that quantifies airborne sound attenuation across interior wall, floor, and ceiling assemblies, ranging from STC 30 (normal conversation heard easily) to STC 50+ (IBC building code privacy standard for multi-family dwellings).
Specification Comparison Table
14 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standards
|
ASTM C518 / ASTM C177 / IECC Chapter 4 / ASHRAE 90.1 | ASTM E90 / ASTM E413 / ISO 717-1 (Weighted Sound Reduction Index Rw) / IBC Section 1206 |
|
R-Value Definition
|
R = Thickness (inches) ÷ Thermal Conductivity (k-factor) in (hr·ft²·°F)/Btu | — |
|
Fiberglass Batts (Standard)
|
R-3.1 to R-3.4 per inch | Density: 0.5–1.0 lb/cu ft | Permeable to air/vapor (Vapor Perm > 50) | — |
|
Mineral Wool / Rockwool
|
R-3.8 to R-4.2 per inch | Non-combustible up to 1,177°C (2,150°F) | Excellent acoustic dampening | — |
|
Expanded Polystyrene (EPS)
|
R-3.6 to R-4.0 per inch | White rigid beadboard | Vapor permeable | — |
|
Extruded Polystyrene (XPS)
|
R-5.0 per inch | Blue/Pink closed-cell board | Moisture resistant, continuous foundation insulation | — |
|
Polyisocyanurate (Polyiso)
|
R-6.0 to R-6.8 per inch | Foil-faced rigid foam | Superior continuous exterior sheathing | — |
|
Closed-Cell Spray Foam (ccSPF)
|
R-6.5 to R-7.0 per inch | 2.0 lb density | Class II vapor barrier (< 0.8 Perm) + structural racking strength | — |
|
STC 30 (Poor / Single Pane)
|
— | Normal conversation heard clearly through wall and easily understood |
|
STC 35 (Basic Interior Partition)
|
— | Standard 2×4 wall with 1/2" drywall on each side (no insulation) | Loud speech heard and understood |
|
STC 40 (Moderate Commercial)
|
— | Standard 2×4 wall + R-13 fiberglass batt insulation | Loud speech heard as muffled murmur |
|
STC 45 (Good Privacy)
|
— | 2×4 wall + batts + double layer 5/8" drywall on one side | Loud speech barely audible |
|
STC 50 (IBC Building Code Minimum)
|
— | Multi-family party wall minimum under IBC 1206 (Staggered studs or Resilient Channel RC-1 + batts) |
|
STC 55–60 (High-Performance Acoustic)
|
— | Double-stud wall (separated 1" air gap) + acoustic batts + Green Glue damping compound | Music bass highly attenuated |