Garage Door Sound Transmission: STC, OITC and What Actually Quiets a Garage

What sound transmission is

Sound is pressure waves in air. When they hit a door, some energy reflects, some is absorbed and some makes the door vibrate and re-radiate sound on the other side. Sound transmission ratings measure how much the door reduces that, in decibels, and express it as a single number.

DASMA’s technical sheet on sound transmission describes two ratings used for façades and their elements: the Sound Transmission Class (STC) and the Outdoor-Indoor Transmission Class (OITC). Both provide an integer that increases as noise reduction increases, and both are logarithmic rather than linear with product thickness ².

How STC and OITC differ

STC, calculated under ASTM E413, is typically applied to partitions exposed to speech, television, radio and office equipment ².

DASMA quotes ASTM’s own caution that STC is not appropriate for sources such as machinery, music and transportation noise from motor vehicles, aircraft and trains ².

DASMA also notes the STC test is performed on an element and does not account for weak points such as penetrations and gaps ².

OITC, calculated under ASTM E1332, is typically applied to exterior walls and façade elements such as windows and doors exposed to transportation noise, and its test encompasses an entire assembly ².

DASMA concludes the OITC rating is more applicable to garage doors than STC ². In practice: traffic rumble is low-pitched, and OITC weights those low frequencies.

Ratings you may see

Example: how much quieter is quieter?

DASMA publishes the perceived change in loudness for changes in STC rating ². The same rule of thumb is commonly used for comparing other single-number ratings.

So a door rated 3 points higher than another will barely sound different. Look for gaps of 5 or more before paying extra for noise alone.

Where noise gets through a garage door

Sound follows air. The perimeter gaps at the jambs, header and floor, and any open section joints, leak far more noise than the panel itself.

That is exactly the weakness DASMA notes the STC lab test leaves out ².

Clopay says a tight seal cuts outside noise and that perimeter and bottom seals help absorb vibrations and keep the garage quieter ³.

The panel matters second. A thin, single-skin steel door vibrates like a drum. Insulated doors damp that: Clopay says garage door insulation dampens noises such as lawn equipment, street traffic and noisy hobbies, and that polyurethane reduces sound ⁴.

What makes a panel quieter

Mass, stiffness and damping. Heavier panels resist being pushed by sound waves; stiffer panels vibrate less; damped panels turn vibration into tiny amounts of heat. A bonded sandwich section adds all three compared with a bare skin, because the core glues two skins together, as DASMA describes for structural sandwich panels ¹.

Windows reduce a door’s rating because glass is lighter and thinner than an insulated section, and frames add joints. Laminated or insulated glass helps, as covered below. See sandwich construction.

Sound transmission vs operating noise

Sound transmission is about outside noise coming in through a closed door. The rattle, squeal and hum you hear when the door moves is operating noise, which comes from rollers, hinges, the opener drive and how the opener is mounted. Chamberlain describes belt drives as ultra-quiet and smooth compared with chain drives ⁵.

If the complaint is a loud door in motion, look at hardware and the opener first. See operating noise.

Where sound ratings are required

For most homes, no code sets a sound rating for the garage door.

DASMA notes the International Green Construction Code Section 807 contains sound transmission provisions, and that while it does not specifically regulate vehicular doors, a door placed in a partition can directly affect the measured STC or OITC, so designers may have to consider it where sound levels are field measured ².

Where a building near an airport, rail line or highway must meet an exterior OITC target, ask the door maker for tested OITC data on the exact model and size.

Decibels in plain terms

Ratings like STC and OITC are built from decibel reductions measured across a range of pitches, then fitted to a reference curve to produce one number.

DASMA describes the result as representing the difference in decibels on one side of a wall or partition versus the other, and stresses the scale is logarithmic, not linear with product thickness ². Doubling a panel’s thickness does not double its rating.

Human hearing is logarithmic too, which is why DASMA’s perception table matters more than the raw numbers.

A change of about 10 points sounds roughly half as loud, while 1 to 3 points is hard to notice at all ².

When a sales sheet shows two doors a couple of points apart, treat them as the same for noise and choose on other grounds.

Rooms above and beside the garage

If the noise problem is in a bedroom over the garage or a room next to it, the garage door is only one path.

Sound also travels through the shared wall, the ceiling, ducts and the door from the garage into the house.

Acousticians call these flanking paths, and they explain why a new door sometimes makes less difference than expected.

Start by finding the loudest path. Stand in the room with the garage door closed and someone running a vacuum or radio in the garage; listen at the wall, the ceiling and the house door.

If the house door is the leak, weatherstripping it may help more than any garage door upgrade. If operating noise is the issue, the opener’s mounting and drive type matter most, and Chamberlain positions belt drives as the quieter option ⁵.

Windows and decorative inserts

Glass is the acoustic weak spot in most doors. It is thinner and lighter than an insulated section, and the frame adds joints and gaskets that can loosen. If quiet matters, choose fewer windows, put them in the top section only, and ask for laminated or insulated glass, which reduces noise better than single panes.

Loose decorative inserts and window frames can also buzz when trucks pass. That is a hardware fix rather than a rating problem: tighten or reseat the inserts. See vision panel.

What helps and what does not

Limits

Few residential door makers publish STC or OITC, and lab STC ignores the gaps that matter most ². Even a well-rated door is one part of the wall; noise also comes through walls, windows and the house door from the garage. Ratings are logarithmic, so small differences are hard to hear ².

What drives cost

No prices on this page. See the cost guide.

• Insulated or sandwich construction.
• Seal upgrades at perimeter and joints.
• Glazing: laminated or insulated glass.
• Testing data for commercial projects.

How to quiet a garage from outside noise

1. Find the gaps: look for light around the closed door at night.
2. Replace worn bottom and perimeter seals ³.
3. Close gapping section joints by having the door adjusted.
4. If replacing the door, choose insulated, bonded sections ⁴.
5. For a strict target, ask for tested OITC data ².

Upkeep

• Inspect seals every three months ³.
• Keep the door adjusted so it closes evenly.
• Tighten loose hardware that rattles in wind.

Warning signs

A garage that suddenly gets louder often has a failed seal or a door that no longer closes evenly. Whistling on windy days points to a gap at the top or sides, and a door that booms in gusts may have loose struts or hinges worth tightening. Check the weatherstripping.

Standards

STC is calculated under ASTM E413, OITC under ASTM E1332, and sound absorption average under ASTM C423 ². The International Green Construction Code addresses sound transmission in Section 807 ².

Single-skin vs insulated door for noise

Myths

Myth STC is the right rating for garage doors.

Reality DASMA says OITC fits better ².

Myth A few rating points make a big difference.

Reality 3 points is just perceptible ².

Myth Acoustic foam stops noise coming in.

Reality Absorption is not a barrier ².

Location

What to do first

Seal the gaps, then consider an insulated door. If you need a number for a project, ask for tested OITC. See polyurethane insulation for the quietest common construction.

Related terms

Operating Noise

Operating noise is the sound a garage door system makes while it opens and closes, coming from rollers, hinges, springs, tracks, loose hardware and the opener, and carried into the house as vibration.

Weatherstripping

Weatherstripping is the set of flexible seals that close the gaps around a garage door, chiefly the perimeter seal along the jambs and header, plus seals at the top, between sections and at the bottom edge.

Sandwich Construction

Sandwich construction is a way of building a garage door section in which an insulating foam core is bonded between an exterior and an interior skin, so the three layers act together as one stiff, insulated panel.

Polyurethane Insulation

Polyurethane insulation, in a garage door, is a foam that makers inject between a door section’s two steel skins, where it expands to fill the cavity and bonds to the skins, insulating and stiffening the section.

Vision Panel

A vision panel is a cutout in a garage or commercial door that is glazed with clear glass or plastic, so people can see through the door and daylight can enter while it is closed.

Also referenced from: Polyurethane Insulation, Operating Noise, Vision Panel