STC: Think voices & TV.
A useful starting point for comparing how a window reduces sounds in the speech-frequency range. It is a rating of the window assembly, not just the glass.
← Training libraryCustomer conversations · Scott’s Field Notes
Understanding window sound ratings.
STC, OITC, and the question to ask before recommending a window.
By Scott Dunfield · October 22, 2026
Start with the customer’s concern
“What sound are you trying to keep out?”
Voices from next door? Trucks passing the bedroom? A nearby train? That answer helps us choose what to compare—not just how many panes of glass to order.
OITC: Think traffic & rumbling trucks.
OITC includes lower-frequency outdoor noise. When a customer mentions engines, trains, or aircraft, pay particular attention to this rating.
Compare the same rating.
Higher numbers indicate better sound blocking within the same rating system. Compare STC to STC and OITC to OITC. The numbers are not percentages and do not promise that a room will be silent.
| Window configuration | STC | OITC |
|---|---|---|
| Lifestyle Triple PaneCasement · 5 / 3 / 4 mm glass | 36 | 31 |
| Impervia FiberglassDual-pane venting casement · 5 / 3 mm glass | 34 | 28 |
These are ratings for the configurations compared—not a rating for every window in either series. Style, size, and glass options can affect performance. Scott can confirm the appropriate configuration and current availability for your project.
What does that mean for your customer?
The Lifestyle configuration shown scores higher in both tests. If traffic is the main concern, its higher OITC rating is especially relevant. That is a starting point for the conversation, alongside the project’s budget, appearance, and other requirements.
The window is one part of the solution.
Glass configuration, the frame, proper installation, and tight seals all matter. Sound can also travel through walls, doors, and other paths. The goal is a quieter home—complete silence isn’t on the order form.
Three questions to bring to the conversation
- What noise bothers the customer most?
- Which rooms and sides of the home are affected?
- What windows are there now, and are there visible gaps or damaged seals?
Sources & tested configurations
Based on Pella’s published sound-performance information, reviewed October 22, 2026.
- Pella sound resistance: Lifestyle triple-pane casement, tested at 23 × 59 inches with 5 / 3 / 4 mm glass, STC 36 / OITC 31.
- Pella Impervia Casement Architectural Design Manual, page F-CM-2: dual-pane venting casement, tested at 23½ × 59 inches with 1-inch glazing and 5 / 3 mm glass, STC 34 / OITC 28.
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