No window makes a house silent, but the right one can cut street noise enough that you’ll notice the difference on the first night. So-called soundproof windows work by combining heavier or laminated glass, unequal pane thicknesses, wider air gaps and an airtight installation.
The numbers to compare are STC and OITC ratings. Higher is quieter, and a jump of about 10 decibels is judged roughly half as loud by most listeners, according to the Federal Highway Administration.
At TurnKey Window we replace windows for homeowners around New Orleans, including glass packages aimed at noise. If traffic, neighbors or nightlife are keeping you up, tell us about your house or call (504) 226-6201.
Key takeaways
- STC and OITC ratings measure how well glass and windows block sound, and higher numbers mean better noise reduction.
- OITC covers lower frequencies down to 80 Hz, which makes it the better measure for road noise, according to glass maker Cardinal.
- Laminated glass and unequal pane thicknesses raise acoustic ratings more than adding a third pane.
- Argon gas has no measurable effect on acoustics, per Cardinal’s technical bulletin.
- Air leaks let sound through, so a tight installation matters as much as the glass.
- For existing windows, sealing gaps and adding a storm window or insert are the most practical upgrades.
How window noise ratings work
Two ratings show up on window and glass spec sheets. Cardinal, an insulating glass manufacturer, explains both in its technical bulletin on glass acoustics.
- STC (Sound Transmission Class) is a single number for how well a material resists sound, measured from 125 Hz to 4,000 Hz.
- OITC (Outdoor-Indoor Transmission Class) measures sound moving from outdoors to indoors, from 80 Hz to 4,000 Hz, which captures more of the low rumble from traffic.
- For both, a higher rating means better sound blocking.
Cardinal adds an important caveat. Its published figures are for the glass alone, and the rating of a finished window is typically lower because the frame and construction affect the result.
What a decibel change feels like
Ratings are in decibels, and decibels don’t scale the way most people expect. The FHWA’s guidance on reviewing noise analysis says a 9 to 10 dB reduction is typically judged half as loud as the original sound.
The same guidance says a change of about 3 dB is usually the smallest people notice without listening for it, and a 5 dB reduction is readily perceptible. So when you compare two windows, a gap of a few points in rating is small, while a gap near 10 points is a real, audible difference.
How much noise different windows block
The FHWA publishes building noise reduction factors that engineers use to estimate indoor noise from highway traffic. They show how much the window condition matters.
| Building type | Window condition | Noise reduction (FHWA) |
|---|---|---|
| Any | Windows open | 10 dB |
| Light frame | Ordinary sash, closed | 20 dB |
| Light frame | Storm windows | 25 dB |
| Masonry | Single glazed | 25 dB |
| Masonry | Double glazed | 35 dB |
If your house is wood frame, the “light frame” rows apply. Adding a storm window to ordinary closed sash gains about 5 dB in that table, which is noticeable but not dramatic.
The FHWA also tells analysts to assume windows are open unless there’s firm evidence they stay closed almost every day. Any window’s rating only helps when it’s shut.
What makes glass quieter
Cardinal’s bulletin lists estimated STC and OITC values for common insulating glass builds. A few rows show the pattern clearly.
| Glass build (outer / air gap / inner) | STC | OITC |
|---|---|---|
| 3 mm / 13 mm / 3 mm, double pane | 31 | 26 |
| 6 mm / 13 mm / 6 mm, double pane | 35 | 30 |
| 6 mm / 13 mm / 7 mm laminated | 40 | 33 |
| 7 mm laminated / 13 mm / 7 mm laminated | 42 | 35 |
| 3 mm / 13 mm / 3 mm / 13 mm / 3 mm, triple pane | 34 | 27 |
The laminated builds post the highest numbers in that set. The triple-pane unit with thin glass scores lower than a double pane with one laminated lite, so more panes isn’t automatically quieter.
Laminated glass
Laminated glass has a plastic interlayer bonded between glass layers, and Cardinal’s figures use standard PVB interlayers. In its data, swapping one 6 mm pane for a 7 mm laminated pane raises a 13 mm double-pane unit from STC 35 to STC 40.
If you’re also thinking about storm protection, our impact-resistant windows page covers impact-rated options.
Unequal pane thickness
Pella’s guide to choosing soundproof windows says mixing glass thicknesses in an insulated glass unit can help improve the STC rating. Pella describes variation in thickness as a basic principle of sound damping.
The same guide says most standard dual-pane glass options rate around STC 26, and that varied-thickness dual glazing can reach the mid-30s.
Wider air gaps, and what doesn’t help
Cardinal’s figures show wider air spaces raising ratings. A 6 mm double pane goes from STC 32 with a 6.5 mm gap to STC 38 with a 19.5 mm gap.
One common assumption doesn’t hold up. Cardinal notes that argon filling has no measurable effect on acoustical properties, so argon is an energy feature, not a noise feature.
Installation matters as much as glass
A quiet glass package won’t perform if sound leaks around it. Pella’s guide sums it up in five words: where air goes, sound goes.
It points to two weak spots: the perimeter of the window frame and the places where gaskets and weatherstripping are installed. A careful install closes both.
- The gap between the new frame and the rough opening is fully insulated and sealed.
- Exterior and interior perimeter joints are caulked continuously.
- Sashes close tightly against their weatherstripping and lock without gaps.
- Any damaged sill or trim is repaired, since a loose trim joint can leak air and sound.
How to soundproof your existing windows
If replacement isn’t in the plan yet, you can still cut some noise. Start with air leaks, since they’re cheap to fix and they let sound through.
- Caulk stationary gaps. The NFRC’s consumer guide on caulking and weatherstripping says caulk seals cracks, gaps and joints no more than a quarter inch wide.
- Weatherstrip the sashes. The same guide says weatherstripping prevents air leaks around window sashes and should go on clean, dry surfaces above 20°F.
- Add a storm window or insert. In the FHWA’s table, storm windows on a light-frame house give about 25 dB of reduction versus 20 dB for ordinary closed sash.
- Repair broken glass and loose glazing. Cracked panes and gaps in old glazing compound let sound and air in.
- Keep the windows shut on noisy nights. The FHWA puts open windows at only 10 dB of reduction.
Working on ladders or removing old glass carries real risk. Leave upper-story work and broken-glass removal to a professional, and see our window repair page if a sash or pane needs fixing.
When replacement makes more sense
Sealing and storm panels help, but they have limits. If your windows are single pane, drafty or rotting, replacement lets you pick a glass build for noise and fix air leaks in one job.
- Bedrooms facing a busy street or a late-night corner
- Single-pane windows where old glazing has failed
- Frames that no longer close tightly
- Homes where you also want impact-rated glass
Our SoftLite windows page notes that SoftLite offers glass options that include impact-resistant and noise-reducing glass. Ask to see the STC and OITC ratings for the full window, not only the glass.
If you live in a local historic district, check the HDLC’s window guidelines first, since the commission reviews replacement of visible exterior windows. Our window replacement page explains how a project starts.
How to compare quotes for noise-reducing windows
Two quotes can both say “sound package” and mean very different things. A few questions on paper make the comparison fair.
- Ask for full-window ratings. Cardinal notes that a finished window usually rates lower than its glass alone, so a glass-only STC can flatter the product.
- Ask which test standards were used. Cardinal lists ASTM E 90 for laboratory sound transmission, ASTM E 1425 for exterior windows and doors, and ASTM E 1332 for OITC.
- Ask for OITC as well as STC. If traffic is your main problem, OITC’s range down to 80 Hz tells you more about low-frequency rumble.
- Ask what the glass build is. Pane thicknesses, air gap width and whether a lite is laminated all show up in Cardinal’s figures.
- Ask how the perimeter will be sealed. A quiet unit installed with gaps around the frame won’t reach its rating.
Matching the upgrade to the noise
Cardinal calls OITC the better measure for low-frequency sound such as road noise. Laminated glass and wider air gaps lift both ratings in Cardinal’s data, so they’re the usual answer for a room facing a busy road.
If the noise is voices or music from a neighbor or a nearby bar, STC is the rating most spec sheets lead with. Tight weatherstripping and a well-sealed frame matter a lot here, since Pella points to gaps around the frame and gaskets as the places sound slips through.
You don’t have to upgrade every window to the same level. You can put the heaviest glass in bedrooms and street-facing rooms and use standard units elsewhere, which keeps the budget in check.
Frequently asked questions
Do soundproof windows actually work?
They reduce noise but don’t eliminate it. Cardinal’s data shows laminated double-pane glass reaching STC 40 to 42 versus 31 to 35 for standard double pane, and the FHWA says a 9 to 10 dB reduction is typically judged half as loud.
How can I soundproof my existing windows?
Seal air leaks first with caulk on stationary gaps and weatherstripping on the sashes, then consider a storm window or insert. The FHWA’s figures show storm windows on a wood-frame house adding about 5 dB of noise reduction over ordinary closed sash.
Is laminated glass or triple pane better for noise?
For noise, laminated glass usually wins. In Cardinal’s estimates, a triple-pane unit with 3 mm glass rates STC 34, while a double pane with one 7 mm laminated lite rates STC 40.
What is a good STC rating for a window?
Pella says most standard dual-pane glass rates around STC 26, and sound-focused builds reach the mid-30s. Cardinal adds that a complete window usually rates lower than its glass alone, so compare full-window ratings.
Does argon gas make windows quieter?
No. Cardinal’s technical bulletin states that argon filling has no measurable effect on acoustical properties, though it’s still useful for energy efficiency.
Get a quieter house with the right glass
The best noise package depends on where the sound comes from and which rooms matter most. We can look at your windows, talk through glass options and give you a free estimate.
Contact us online or call (504) 226-6201 to set up a visit.