| Glazing | Approx. STC |
|---|---|
| Single 1/4 in glass | 29–31 |
| Laminated 1/4 in glass | 34–36 |
| Standard insulated unit (1 in) | 32–35 |
| Laminated insulated unit | 37–40 |
| Secondary glazing, 4 in+ air gap | 45–50 |
Wider air gaps help more than thicker glass, and panes of different thickness avoid a shared resonance. Seal the frame to the opening with acoustic sealant.