A standard cam lock holds the two sashes of a double hung window together and stops the window being opened from outside. What it does not do is limit how far the window opens once unlocked, which is why it does not satisfy the window safety device requirements that apply to residential strata buildings in New South Wales. Security and fall prevention are separate problems requiring separate hardware, and on a double hung window both usually apply.
Why locking a double hung window is different
A double hung window has two sashes in the same frame, one in front of the other, both able to slide vertically. In many Australian aluminium versions only the bottom sash operates, but the principle is the same.
The two sashes meet at a horizontal rail partway up the window, and that meeting rail is where the lock sits. This is a different arrangement from a hinged awning or casement window, where the sash compresses into the frame and the lock holds it there.
The consequence is that most double hung window locks secure the sashes to one another rather than to the frame. That distinction matters more than it sounds, and it is the source of most confusion about what these locks actually achieve.
The standard cam lock
The classic double hung window lock is a cam or crescent lock mounted on the meeting rail. A curved cam rotates from a lever on the inner sash and draws a keeper on the outer sash toward it.
It does two useful things. It pulls the sashes tightly together, which improves the weather seal at the meeting rail and reduces rattle. And it prevents the bottom sash being slid up from outside.
It also has two limitations worth understanding.
It secures the sashes to each other, not to the frame. A determined attempt to lever the whole sash assembly is resisted by the sash tracks rather than by the lock.
And it provides no control over how far the window opens. Once released, the sash slides its full travel, which on a double hung window is typically a very large opening with a low sill. That is precisely the configuration that creates a fall risk.
NSW window safety devices in strata buildings
This is the requirement most owners of apartments and older Sydney homes are not aware of, and double hung windows are among the most commonly affected.
What is required. Residential strata schemes in New South Wales must have compliant window safety devices fitted where a window opening is more than two metres above the surface beneath it and less than 1.7 metres above the internal floor. The device must limit the opening to a gap not exceeding 12.5 centimetres and must be robust enough to resist a specified outward force. The compliance deadline passed in March 2018.
Who is responsible. The obligation sits with the owners corporation, and it covers windows in individual lots as well as common property. Lot owners must not remove or interfere with a fitted device.
What does not count. A standard cam lock does not satisfy the requirement, because it does not restrict the opening. Neither does a flyscreen, which is not designed or tested to resist force. Locking the window permanently shut is not an acceptable solution either, since the device must be capable of being released by an adult.
Why double hung windows matter here. A double hung window in an apartment or a first floor bedroom frequently meets both conditions. The sill is low, often well under 1.7 metres from the floor, and the opening above ground is often well over two metres. The sash slides up to create a large clear opening. It is the classic configuration the requirement exists to address.
Requirements are periodically amended, so confirm the current position with NSW Fair Trading, your owners corporation or a strata professional rather than relying on a summary.
Restrictors and limit stops
The hardware that addresses fall risk is a restrictor, sometimes called a limit stop or sash stop.
Fixed restrictors limit the sash to a set opening and hold it there permanently. Simple and reliable, but the window can never be fully opened without removing the device.
Releasable restrictors limit the opening under normal use but can be released by an adult using a key or a deliberate two stage action a child cannot replicate. This is the type generally used to meet safety device requirements, since it addresses fall risk while preserving the ability to open the window fully for cleaning, maintenance or escape.
Sash stops are pins or blocks fitted into the sash track that physically prevent travel beyond a set point. Some are removable, some are keyed.
The design tension is the same one that runs through all safety hardware. The device must be beyond a child’s ability to release and within an adult’s, and it must not turn the window into a permanent barrier where it forms part of an escape route.
Security locks for double hung windows
Fall prevention and security overlap but are not the same, and a window may need both.
Keyed cam locks are the standard security upgrade. The cam operates as normal but requires a key to release, which prevents the window being opened by someone reaching through a broken pane or an open adjacent window.
Sash bolts are bolts driven through the inner sash stile into the outer sash or the frame, holding both against vertical movement. They resist levering better than a cam lock does, because they engage the frame rather than only the other sash.
Keyed sash stops serve double duty, limiting the opening for safety and requiring a key to remove for security.
As with any keyed hardware, egress matters. A keyed window lock on a bedroom window that forms part of an escape route needs its key kept adjacent and known, or it becomes a hazard. We set out the same reasoning for doors in our article on thumb turn locks for aluminium sliding doors.
Hardware manufacturers used in Australia
Window hardware is a distinct market from door hardware, with its own specialists.
Whitco, part of Allegion, is among the most widely used window hardware manufacturers in Australia, supplying sash locks, restrictors and window furniture across residential aluminium suites.
Doric supplies window and door hardware matched to the major commercial aluminium suites.
Lockwood, part of the ASSA ABLOY group, produces locking hardware used extensively across Australian residential and commercial applications.
Hardware is generally distributed through Lincoln Sentry and Access Hardware, which stock across these brands.
Coastal and maintenance considerations
Window hardware is smaller and lighter than door hardware, which makes it more vulnerable to corrosion rather than less.
Cam locks and restrictors use small springs, pins and cast components. Near the coast, in the eastern suburbs, Northern Beaches and Sutherland Shire, these seize considerably faster than door hardware does, and a seized restrictor is a compliance problem as well as an inconvenience.
Specify stainless or marine grade components where available. Operate every lock and restrictor through its full travel a few times a year. Use a dry lubricant such as a PTFE based product rather than an oil spray, which attracts dust and eventually gums the mechanism.
If a sash has become stiff or no longer aligns with its lock, the cause is often the sash itself rather than the hardware. We cover that in our article on fixing a loose or tight double hung window sash.
When the window cannot be made compliant
Some older double hung windows cannot accept a compliant safety device without modification, or the sash and frame have deteriorated to the point where fitting one is not viable.
Where a window is also draughty, difficult to operate or single glazed, replacement frequently makes more sense than fitting hardware to a unit that needs replacing anyway. A modern double hung window can be supplied with compliant restrictors integrated rather than added, and the compliance question is resolved at the same time as the performance one.
Our double hung windows are manufactured in Villawood, and window replacement includes assessment of what your existing openings will and will not accommodate.
Choosing, in short
Start by establishing whether a safety device is required. If the property is a residential strata scheme in New South Wales and the window sits more than two metres above the ground outside with a sill less than 1.7 metres above the floor, a compliant restrictor is not optional.
Add a keyed cam lock or sash bolt where security is a concern, particularly on ground floor and accessible windows.
Choose releasable restrictors over fixed ones wherever the window forms part of an escape route or needs to open fully for cleaning.
Specify corrosion resistant components near the coast, since window hardware is small and fails early.
And if the window itself is at the end of its life, resolve the compliance and the performance questions together rather than fitting new hardware to an old unit.
Frequently asked questions
Does a standard window lock meet NSW safety device requirements?
No. A cam lock secures the window closed but does not limit how far it opens once unlocked. The requirement is for a device that restricts the opening to no more than 12.5 centimetres and resists a specified force.
Who has to pay for window safety devices in a strata building?
The obligation sits with the owners corporation, which covers windows in lots as well as common property. Individual owners must not remove devices once fitted. Confirm the current position with your owners corporation or NSW Fair Trading.
Can I fit a restrictor to an existing double hung window?
Usually yes, on both aluminium and timber windows, provided the sash and frame are sound. Older or deteriorated windows sometimes cannot accept one without modification.
Do window safety devices apply to houses as well as apartments?
The mandatory requirement applies to residential strata schemes. In a freestanding house there is no equivalent obligation, but the fall risk is identical and a restrictor is worth fitting on upper level bedroom windows regardless.
Are keyed window locks a fire risk?
They can be if the window is an escape route and the key is not immediately available. Keep the key adjacent and in a known position, or use a releasable restrictor that an adult can operate without a key.
Why has my window lock become stiff?
Corrosion is the usual cause near the coast, particularly if an oil based lubricant has been used. A sash that has dropped or swollen so the lock no longer aligns is the other common reason.