Our Brisbane infill site is mapped as noise category 2 under the transport noise corridor rules. The acoustic consultant has specified glazing, but the architect wants bigger bedroom windows. What ratings does the envelope need, and does window size change the glazing requirement?

Yes, window size can change the glazing requirement. At Noise Category 2, the glazing to a habitable room needs Rw 32 while the room's total glazing is 1.8 m² or less, and Rw 35 once it goes over 1.8 m². [1] If the consultant specified to the lower band and the architect's bigger windows take a bedroom over the line, the glazing has to be re-specified.

The instrument that sets the numbers. The acoustic ratings come from Queensland Development Code MP 4.4, Buildings in a Transport Noise Corridor, not from the NCC. [1] The NCC still governs the glass for wind loading and human impact, which is a separate check covered below. [2]

The Category 2 envelope ratings. A Category 2 site needs a minimum transport noise reduction of 30 dB(A) for habitable rooms, delivered through minimum ratings for each component of the external envelope: [1]

• Glazing: Rw 35 where the total area of glazing for a habitable room is greater than 1.8 m²; Rw 32 where it is less than or equal to 1.8 m²
• External walls: Rw 41
• Roof: Rw 38
• Floors: Rw 45
• Entry doors: Rw 33

Only the glazing figure moves with window size. The wall, roof, floor and door ratings stay the same however big the windows get.

How the 1.8 m² is measured. The test is the total area of glazing for a habitable room, not the size of any one window. [1] Every window serving the bedroom counts toward the same total, so two modest windows can tip a room over the line just as one large one can. Exactly 1.8 m² stays in the Rw 32 band; the Rw 35 band starts above it. The table does not say whether glazing area means the visible glass or the frame opening, so agree the measurement basis with your consultant and certifier before you rely on a room sitting just under 1.8 m².

Rw means Rw. The table sets a minimum Rw for each component, not Rw + Ctr. [1] If a window supplier quotes a different metric, such as Rw + Ctr, ask for the plain Rw figure to compare against the table rather than assuming the two match.

A separate safety check on the glass. Whatever the acoustic rating, the glazing must also satisfy NCC Volume Two: Part 8.3 of the Housing Provisions or AS 1288 for the glass, and AS 1288 and AS 2047 or Part 8.4 for human impact. [2] Under Part 8.3, glass thickness depends on the site's wind classification and the panel dimensions, so bigger panes can drive thicker glass for reasons that have nothing to do with noise. [3] Both checks have to pass.

Practical next step. Before the window schedule is locked, total the glazing for each bedroom and other habitable room against 1.8 m², then ask the acoustic consultant to confirm each room's glazing meets Rw 35 or Rw 32 as the totals require. Have the window supplier confirm the same panes also work for the site wind class.

Edition note. Queensland is on NCC 2022 Amendment 2 until 30 April 2027, and NCC 2025 takes effect from 1 May 2027 with no election window. The Queensland Development Code applies alongside whichever NCC edition is in force, but whether current QDC settings carry over unchanged after 1 May 2027 is not yet confirmed. [4] The MP 4.4 text relied on here is Version 1.1, published 17 August 2015, so confirm with your certifier that no later version applies to your project.