DASMA TDS 189 - Sound Transmission and STC Ratings for Garage Doors

Homeowners who convert a garage into a music room, home office, or workshop often ask how much sound a garage door blocks. DASMA TDS 189 answers that question with a standardized metric and explains what affects the real-world result.

What this data sheet says

DASMA TDS 189 covers Sound Transmission Class (STC), the standard rating system for how much a building assembly reduces airborne sound. STC is tested by measuring how much sound energy a panel blocks across a range of frequencies. Higher numbers mean better noise reduction.

"The STC rating is the single-number rating derived from testing a door assembly per ASTM E90 and calculated per ASTM E413."

Key points from the TDS:

• A non-insulated steel door typically achieves STC values in the low 20s.
• An insulated door with a bonded foam core generally scores in the mid-to-upper 20s.
• The door itself is rarely the weakest link; gaps at the sides, top, and bottom of the opening often allow more sound transmission than the door panel.
• STC ratings for garage doors are not universally published. Many manufacturers do not test to ASTM E90 and E413, so consumer comparisons are limited.

The TDS clarifies that the R-value (thermal insulation) and STC rating of a door are related but not the same thing. A higher-R door often has a denser or thicker foam core, which can improve STC, but the relationship is not linear and should not be assumed.

When it applies

Sound control matters in several real-world situations:

Attached garage next to a bedroom or home office. When the sleeping or working area shares a wall with the garage, traffic noise, door operation, and mechanical equipment from the garage pass through the structure. A higher-STC door reduces, but does not eliminate, that transmission.

Garage workshop or band practice space. If the garage generates sound rather than receives it, the concern reverses: containing noise to avoid neighbor complaints or HOA issues. The door is one part of the total envelope; walls, ceiling, and seals matter equally.

Denver urban infill. In the Highlands, Congress Park, and South Platte River corridor neighborhoods, newer attached garages sit close to sidewalks and neighboring homes. A well-sealed, insulated door reduces both noise in and noise out.

What this means for you

STC in the high 20s is the realistic ceiling for a garage door. Even the best insulated residential sectional door will not approach the STC 50+ values of purpose-built soundproof assemblies. Set realistic expectations.

Seal quality matters as much as panel STC. A door with excellent panel ratings but poor bottom seal or worn side weatherstripping will underperform a lower-STC door that is tightly sealed all the way around.

Ask for ASTM E90 test data, not marketing language. Terms like "quiet" or "sound-dampening" are not standardized. If sound control matters for your project, ask the dealer for the actual STC test result or the ASTM report number.

G Brothers can recommend insulated door options with known STC performance and can inspect weatherseal condition for Denver homeowners trying to reduce noise from or into their garages.

Full text and source

Download DASMA TDS 189 from the official TDS index at https://www.dasma.com/technical-data-sheets/.

This entry covers airborne sound transmission through residential sectional garage door panels. Impact noise, operator noise, and structural-borne vibration are separate topics not addressed in TDS 189.