The certifier flagged that our first-floor bedroom windows need opening restrictors even though the sills are 900 mm above the floor. When do openable bedroom windows need fall protection, and do screens count?

The certifier is right, and the sill height is not what decides it. Fall protection is triggered by the drop below the window, not by how high the sill sits. Where the floor below the window is 2 m or more above the surface beneath, protection is required, and a first-floor bedroom will almost always clear that. [1]

Two different measurements are doing two different jobs, and conflating them is where this argument usually starts:

• The 2 m drop, measured from the floor of the room down to the surface beneath, decides whether the provision applies at all. Where that drop is less than 2 m, there are no specific requirements. [1] [2]
• The 1.7 m opening height, measured from the floor of the room up to the lowest level of the window opening, decides whether you have to fit anything. A device or screen is only required where the opening starts less than 1.7 m above the floor. [1]

A 900 mm sill puts the opening well under 1.7 m, so the exemption does not apply and something must be fitted.

Do screens count? Yes. The provision gives you two alternatives for the openable portion: a device that restricts the opening, or a screen with secure fittings. Whichever you choose, it must: [1]

• not permit a 125 mm sphere to pass through the window opening or the screen;
• resist an outward horizontal action of 250 N;
• have a child-resistant release mechanism, but only where it can be removed, unlocked or overridden.

That last condition opens the branch that catches people out:

• If the screen or device can be removed, unlocked or overridden, you also need a barrier not less than 865 mm above the floor. It must not permit a 125 mm sphere through, and must not have horizontal or near-horizontal elements between 150 mm and 760 mm above the floor that could be climbed. [1]
• If it is securely fixed so it cannot be unlocked or overridden without tools, it is treated as a fixture and the 865 mm barrier is not required. [2]

Your 900 mm sill does earn its keep here, just not in the way the question assumed. A wall or fixed glazing beneath the openable part can itself serve as the 865 mm barrier where it meets the criteria, and at 900 mm the sill wall clears the 865 mm minimum. [2] The margin is only 35 mm, so confirm the as-built dimension from finished floor level rather than working off the drawings.

Where the screen or device is installed so it can be removed for cleaning or emergency egress, the unlocking mechanism has to be child resistant. That can be achieved by requiring a tool or key, or by a coordinated two-handed operation. [2]

NSW is on NCC 2022 Amendment 2 and moves to NCC 2025 on 1 May 2027. The substantive requirements are identical in NCC 2025: same 2 m trigger, same 1.7 m exemption, same 125 mm, 250 N and 865 mm figures. NCC 2025 adds explanatory text confirming that "window" here captures openings that do not admit light, such as metal louvres, and adds a separate provision, 11.3.8, covering rooms other than bedrooms, where protection is triggered at a 4 m drop rather than 2 m. [3]

One caution on the drop itself: what counts as the surface beneath is not always the ground. Where there is a roof or a ledge below the window, have the certifier confirm what the 2 m is being measured to before you rely on it. [4]