Side-by-Side Comparison
Thermal Insulation & Acoustics
Roof Pitch & Slope Standards vs. Sound Transmission Class (STC) Ratings
Comparing 2 standards across 13 specifications. 13 key differences identified.
Comparing:
Roof Pitch & Slope Standards
Sound Transmission Class (STC) Ratings
Roof pitch is standardized under the International Building Code (IBC) and IRC into rise-over-run slope ratios (e.g. 4:12 indicates 4 inches of vertical rise per 12 inches of horizontal run), defining pitch angles from 0° to 60° and determining mandatory weatherproofing coverings (membrane vs asphalt shingles vs metal).
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
13 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standards
|
IBC Chapter 15 (Roof Assemblies) / IRC Section R905 / OSHA Roofing Fall Protection | ASTM E90 / ASTM E413 / ISO 717-1 (Weighted Sound Reduction Index Rw) / IBC Section 1206 |
|
Notation Formula
|
Rise in inches per 12 inches of horizontal run (e.g. 4:12 or 4/12) | — |
|
Flat / Low-Slope Roof
|
1/4:12 to 2:12 (1.19° to 9.46°) | Requires continuous welded membrane (TPO, EPDM, PVC, Built-Up BUR) | — |
|
Conventional Slope (Shingle Minimum)
|
4:12 to 8:12 (18.43° to 33.69°) | Standard 3-Tab and Architectural asphalt fiberglass shingles with single underlayment | — |
|
Low-Slope Shingle Exception
|
2:12 to 4:12 (9.46° to 18.43°) | Asphalt shingles permitted ONLY with double layer underlayment or self-adhering ice/water shield | — |
|
Steep Slope Roof
|
9:12 to 12:12 (36.87° to 45.00°) | Excellent snow shed, Mansard/A-frame roofs | — |
|
Walkability / OSHA Threshold
|
≤ 6:12 (26.56°): Walkable by foot | > 6:12: Mandatory OSHA roof brackets and fall arrest harness | — |
|
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 |