DS255 | Sliding Window Limiter

Why Window Restrictors Are Required

The National Construction Code (NCC) requires window opening control devices on openable windows in residential buildings where the floor level is 2 metres or more above the finished ground level below, and where the window could create a fall risk for children or occupants.

The requirement applies specifically to windows where a 125mm sphere can pass through the opening when the window is fully open. The NCC mandates that any compliant window opening control device must restrict the window so that a 125mm sphere cannot pass through the opening, and must withstand an outward force of at least 250N without releasing.

This is not a guideline. For residential buildings subject to NCC Volume 1 and Volume 2, Part F4.4, and for projects specified to AS 5203:2016, compliance is a certification requirement. A building cannot be certified as compliant if windows requiring restriction are not fitted with tested, conforming devices.

The DS255 is designed and tested to meet these requirements for aluminium sliding windows in residential multi-storey buildings.

Application and Project Fit

The DS255 is the correct specification for the following project contexts:

Multi-storey residential buildings where aluminium sliding windows are installed at floor levels 2 metres or more above the finished ground level. This includes apartments, townhouses, medium-density developments, and any residential building where NCC Part F4.4 window restriction requirements apply.

Strata and body corporate managed properties where window compliance across multiple dwellings must be maintained and documented. The DS255’s key-operated release allows building managers and maintenance staff to override the restriction for cleaning and maintenance without removing the limiter permanently.

Retrofit compliance upgrades on existing buildings where windows were installed prior to current NCC requirements and are now required to meet compliant restriction standards. The DS255 installs into the top rail of the sliding window without frame modification.

Schools, childcare facilities, and aged care settings where child safety window restriction is a project requirement under both the NCC and duty-of-care obligations, regardless of the specific storey height trigger.

How the DS255 Works

Restriction setting: The DS255 is installed into the top rail of the aluminium sliding window frame. During installation, the position of the stop body is set by the installer to restrict the window to the required opening distance, typically 100mm to 125mm, to comply with NCC requirements. Once set, the window can be opened and closed freely within a restricted distance without the device needing to be unlocked.

Key-operated removable body: The DS255 features a key-operated removable body, the central innovation that distinguishes it from simpler non-keyed restrictors. The body can be fully separated from the window frame using the key for two specific purposes: emergency egress, where the window must be fully openable, and window cleaning, where full access to the glass is required.

This is a critical specification advantage. Non-removable restrictors that cannot be released without tools can create an emergency egress liability, particularly in apartments and strata buildings where windows may be designated egress paths. The DS255’s key-operated release addresses this directly; the restriction functions as required under normal conditions, and can be overridden with the key when full opening is legitimately required.

Keyed alike capability: The DS255 can be keyed alike to suit other Doric locking devices. For strata managers and property managers operating across a development, keyed alike means one key operates all window limiters throughout the building, eliminating key proliferation at handover and simplifying ongoing facilities management.

Compliance and Testing

The DS255 is designed to satisfy NCC Volume 1 and Volume 2 Part F4.4 window opening restriction requirements for residential aluminium sliding windows in multi-storey buildings.

The Doric window limiter range, which includes the DS255, is tested to the following standards:

• AS 5203:2016 — Protection of openable windows for child safety
• NCC Volume 1 and 2, Part F4.4 — Window opening restrictions
• Load rating: Tested to 250N outward force — the minimum force resistance required by the NCC for compliant window opening control devices
• Cycle testing: Over 25,000 open/close repetitions — verified mechanical performance across the operational life of a residential window installation

For certifiers and project managers, the DS255’s compliance context is straightforward: it is designed for aluminium sliding windows in residential multi-storey buildings, which triggers the NCC restriction requirement.

Installation

The DS255 is designed to be easily installed into the top rail of the sliding window frame. No specialist tooling or frame modification is required for a standard installation.

The installation position determines the restriction distance. The installer sets the stop point during fitment to restrict the window to the required opening distance. Once installed, the device operates passively — the window restricts to the set distance without any end-user action.

Download the DS255 Technical Specifications document for full installation dimensions and fitment guidance.

What NCC requirement does the DS255 satisfy?

The DS255 is designed to satisfy NCC Volume 1 and Volume 2, Part F4.4, which requires window opening control devices on openable windows in residential buildings where the floor level is 2 metres or more above the finished ground level below. The device must restrict the window so that a 125mm sphere cannot pass through the opening, and must withstand an outward force of at least 250N without releasing. The DS255 is designed and tested to meet these requirements on aluminium sliding windows.

What is the opening distance the DS255 restricts the window to?

The restriction distance is set by the installer at the time of fitment. For NCC compliance, the device should be set to restrict the opening to 125mm or less — the maximum opening through which a 125mm sphere cannot pass. The DS255’s adjustable stop allows the installer to set the precise restriction distance required for the specific window configuration and compliance requirement.

How is the DS255 removed for emergency egress or cleaning?

The DS255 features a key-operated removable body. Using the supplied key, the body of the device can be separated from the window frame entirely, allowing the window to be fully opened. This is the mechanism used for both emergency egress situations, where full window opening is required, and for routine window cleaning, where full glass access is needed. No tools are required — the key is the only item needed for removal.

Can the DS255 be keyed alike to other locks in the building?

Yes. The DS255 can be keyed alike to other Doric locking devices. For strata managers and property managers responsible for multiple dwellings, keyed alike means a single key operates all DS255 window limiters throughout the property alongside other Doric door and window hardware. This eliminates key proliferation at handover and simplifies ongoing building management.

Is the DS255 suitable for retrofit installations on existing buildings?

Yes. The DS255 is designed for installation into the top rail of the existing aluminium sliding window frame without frame modification. For buildings where windows were installed prior to current NCC requirements and now require a compliant window opening control device, the DS255 is a direct retrofit solution. Confirm the existing window frame profile accommodates the DS255 against the Technical Specifications before ordering.

What is the difference between the DS255 and the DS255U Narrow Sliding Window Restrictor?

The DS255U is a narrow-profile version of the sliding window restrictor designed specifically for slimline aluminium window frames where the standard DS255 profile does not suit the frame width. If the window frame has a narrow top rail, the DS255U is the correct specification. Confirm the frame dimensions against the DS255 Technical Specifications to determine which product suits your installation.

Does the DS255 affect the ability to ventilate the room?

No. The DS255 restricts the window to the set opening distance — typically 100mm to 125mm — which still allows ventilation through the window opening. The purpose of the device is to prevent the window from opening beyond the compliant distance, not to prevent ventilation entirely. The window operates freely to the restricted opening and can be ventilated at that distance under normal circumstances.

What is the lead time for the DS255?

The estimated lead time for the DS255 is 6 days.