A standard aluminium window with 4–6 mm glass rates about Rw 26–32. Upgrading to 10.38 mm laminated or an acoustic laminate lifts it to about Rw 33–37, and a double-glazed unit with a laminated pane reaches about the same. Awning and casement windows seal tighter than sliders, so with the same glass they score a point or two higher.
Rw by glass type
Typical laboratory results for aluminium windows from published Australian window test data. Real results depend on the frame, seals and installation.
| Glass | Typical Rw | Typical Rw+Ctr |
|---|---|---|
| 4–6 mm float | 26–32 | 25–29 |
| 6.38 mm laminated | 29–34 | 25–32 |
| 10.38 mm laminated | 34–36 | 32–34 |
| 6.5–10.5 mm acoustic laminated | 32–37 | 29–34 |
| Double glazed 6/12/6 | 32–35 | 27–32 |
| Double glazed 6/12/6.38 laminated | 33–37 | 29–31 |
Window type matters as much as glass
Awning, casement and tilt-and-turn sashes clamp shut onto compression seals. Sliding windows and doors brush past pile seals, which leak more sound. With the same laminated glass, test results put awning windows about 1–2 points ahead of sliders. On a busy road, choose an opening window that clamps shut, such as casement or tilt and turn, and use fixed panes where you don’t need ventilation.
What the numbers mean in a bedroom
A 10-point increase in Rw roughly halves how loud the noise outside sounds. Going from a basic slider with 4 mm glass to a casement with 10.38 laminated is about that step. Going further usually needs double glazing with a laminated pane and careful sealing around the frame.
Gaps undo good glass
Sound finds the weakest path. Seal the gap between frame and wall fully, keep weep holes but use baffled ones on noisy facades, and make sure sashes are adjusted to close firmly. See installing supply-only windows.
Questions builders ask
What Rw rating does a standard aluminium window get?
About Rw 26–32 with single 4–6 mm glass, depending on the window type and seals. Awning and casement windows sit at the top of that range, sliders at the bottom.
Is double glazing better than laminated glass for noise?
Not automatically. A double-glazed unit of two 6 mm panes tests at about Rw 32–35, much the same as 10.38 laminated at Rw 34–36. The biggest gains come from laminated glass in the unit, an acoustic interlayer, and a window that seals tightly.
What is the difference between Rw and Rw+Ctr?
Rw is the single-number sound rating. Rw+Ctr adjusts it for low-frequency noise such as traffic and trucks, so it is usually 2–6 points lower. Road and aircraft noise reports normally set targets in Rw+Ctr.
My planning permit has an acoustic report. What do I send?
Send the report or the Rw / Rw+Ctr targets for each room with your plans. That lets the quote match the glass and window type to each room’s target.