Two numbers appear again and again in NSW child window safety conversations: 125mm and 250N. For property managers, strata managers and owners corporations, understanding these numbers makes it easier to know why a simple visual check is not enough.
The 125mm rule refers to the window opening limit. In practical terms, the safety device must stop the relevant window opening more than 12.5 centimetres. This is intended to reduce the risk of a child being able to fall through the opening. Some people refer to this as the 12.5cm rule and others call it the 125mm rule. They mean the same thing.
The 250N requirement relates to strength. NSW Government guidance describes this as a force equivalent to 25 kilograms. A device needs to be able to resist that force. This matters because a device that looks present but is loose, poorly fixed or attached to a damaged frame may not provide the level of protection expected.
For a manager, the practical issue is evidence. You need to know whether the safety device is present, whether it is operating, whether it appears securely fixed, whether the opening is limited and whether anything needs rectification. A report should record the inspection result rather than simply saying “locks installed”.
Common failures include restrictors fitted with loose screws, devices installed on damaged timber, missing keys, windows opening wider than intended, devices residents have disengaged, hardware that no longer catches properly and windows where a standard flyscreen has been mistaken for a safety device.
Haven Compliance inspects child safety window locks and restrictors across Sydney and NSW. Where hardware needs repair or replacement, Haven works with Remsafe, the largest window lock supplier in Australia, to support compliant outcomes and practical rectification.
Why the rule matters
The 125mm and 250N requirements give managers a practical way to think about window safety: the window opening needs to be limited, and the device needs to be strong enough to perform its role. Both parts matter.
If you need a building-wide inspection or reinspection after repairs, contact Haven Compliance for a quote.
Why a tape-measure mindset is not enough
The opening limit is important, but managers should not reduce window safety to one measurement. A device can limit the opening on the day it is installed and still become unreliable if it loosens, breaks, is disengaged or is attached to a damaged frame. The opening limit and force requirement need to be considered together with the condition of the device and the window.
In practical inspections, Haven looks for the obvious signs that a device may not be performing as intended. This includes loose screws, cracked timber, bent components, missing keys, disengaged restrictors, awkward operation, resident modifications and windows that can open beyond the intended limit.
How to explain this to owners and tenants
The easiest way to explain the rule is this: the window needs a device that restricts how far it opens, and that device needs to be strong enough to do its job. A normal flyscreen is not the same thing. A lock that is broken or loose is not enough. A report from years ago may not reflect today’s condition.
For strata managers, this explanation helps committees understand why inspections and reinspection matter. It also helps owners understand why a building may need rectification even when devices appear to be installed.
What the Haven report should show
The report should show inspected areas, defect photos, device condition notes, inaccessible areas and recommended next steps. Where measurement or force testing is relevant, the report should use plain language so a non-technical reader can understand why the item needs attention.
Final note for managers
If a building has old hardware, mixed window types or no recent inspection record, do not guess. A short site inspection and clear report can prevent confusion later. The most useful outcome is not just knowing the rule; it is knowing which windows in the actual building need action and which items can be recorded as inspected.
