Window restrictors are fitted to more than a million UK properties, required by building regulations in schools, care homes and HMOs, and recommended by police for every home with children under five. They prevent falls by limiting how far a window opens, typically to 100mm. But they also create a problem that the regulations do not address: a 100mm gap does not provide meaningful ventilation. On a hot July night, it is barely enough to notice. LockLatch® takes a different approach. It restricts the window and fastens it open but locked at a predetermined gap, adjustable from 9 to 17 centimetres, wide enough for genuine airflow, too narrow for entry, and held in position by a lockable pin.
What UK Building Regulations Require
Approved Document K of the Building Regulations covers protection from falling. Where a window is more than 600mm above internal floor level with an external drop of more than 600mm, measures must prevent falls. The standard solution is a restrictor that limits the opening to 100mm, the maximum gap through which a child’s body cannot pass. The restrictor must be releasable only by a key or tool, not by a child.
Window restrictors are legally required in schools, care homes, hospitals and health and social care premises. In HMOs, many local authorities mandate them as a licensing condition. In private homes, they are strongly recommended where children under five are present. RoSPA reports that properly installed restrictors reduce child falls from windows by 80 percent.
Types of Window Restrictor
Cable restrictors are the most common retrofit option. A steel cable connects the frame to the sash, limiting opening distance. Premium cable restrictors can withstand 3,000 to 4,600 Newtons of force. Friction stay restrictors are built into hinged window mechanisms. Concealed restrictors hide inside the frame for a clean appearance. Hook-and-catch restrictors are the simplest and weakest type. Sash stops fix to the frame at a set height to prevent a sliding sash from opening further.
All of these share one characteristic: they restrict how far a window opens. They are designed to prevent falls. They are not designed to provide ventilation.
The Ventilation Gap
A 100mm opening provides minimal airflow. On a warm evening, it is not enough to cool a bedroom. During cooking, it is not enough to clear steam. In a bathroom, it is not enough to prevent condensation. Trickle vents help with passive background ventilation but cannot replicate the air exchange of an open window. Millions of UK homeowners face the same choice every summer night: comply with the restrictor and sleep in a stuffy room, or disengage it and accept the security risk.
Are Window Restrictors a Legal Requirement
In private homes, no. There is no law requiring homeowners to fit window restrictors. But the picture changes for other property types. Schools and educational establishments must comply with Approved Document K wherever children are present. Care homes, hospitals and health and social care premises fall under HSE guidance on falls from windows. HMOs are subject to local authority licensing conditions, and many councils mandate restrictors on upper-floor windows as a condition of the licence. The Renters’ Rights Act 2025 has strengthened tenant safety protections further.
For landlords, the Housing Health and Safety Rating System categorises falls from windows as a potential Category 1 hazard. An assessment that identifies this hazard can require the landlord to fit restrictors regardless of whether the local authority has made it a licensing condition. In practice, fitting restrictors to any property with upper-floor windows is the safest legal position.
What Most Restrictors Get Wrong
The standard window restrictor is designed for one scenario: preventing a child from falling. It does this well. A 100mm opening stops a child’s body from passing through. But the same device creates three problems it was not designed to solve.
First, ventilation. A 100mm gap in a bedroom window on a warm July night does not provide enough airflow to sleep comfortably. Homeowners disengage the restrictor and open the window fully, defeating the safety purpose. Second, security. A restrictor that limits the opening to 100mm does not lock the window at that position. Most can be pushed or prised wider with a simple tool, which is why the night vent position on uPVC windows does not meet Secured by Design standards. Third, flexibility. A cable restrictor has a fixed length. A sash stop sits at one height. Neither allows the homeowner to choose a wider opening when conditions allow it or a narrower opening when conditions require it.
How Much Do Window Restrictors Cost
Budget cable restrictors and plastic catches start from a few pounds and are available at any hardware retailer. Mid-range key-operated cable restrictors typically cost between 15 and 35 pounds. Premium rigid arm restrictors and security-rated models range from 25 to 50 pounds. Professional installation, if required, adds 15 to 30 pounds per window. Most restrictors are simple DIY installations requiring only a screwdriver and a drill.
How LockLatch® Solves Both Problems
LockLatch® restricts the window AND fastens it open at a predetermined gap. The standard model adjusts from 9 to 17 centimetres. MiniLatch® adjusts from 4.5 to 8 centimetres. Both comply with the 100mm child safety rule: 90mm between the footplates, less approximately 30mm because the footplates are not fixed at the very edge of the frame. The effective opening sits well within the regulatory threshold.
Both products are made from C304 rust-resistant stainless steel with a lockable pin that holds the arm firmly in position. Installation takes about 15 minutes per window with four holes, using one-way security screws on wood and steel frames and pop rivets on uPVC and aluminium. It fits any window or door whatever the frame is made from and whichever way it opens, and supplements the existing window lock rather than replacing it.
How It Compares
A cable restrictor limits the window to a fixed opening with no adjustability or rigidity. LockLatch® lets the homeowner choose their opening and lock it there. LockLatch® retrofits to any existing window in about 15 minutes. No other product on the UK market offers adjustable, locked-open ventilation across all window types with a lifetime guarantee.
The 100mm rule exists for good reason. But ventilation matters too. LockLatch® and MiniLatch® provide both: compliance with the 100mm child safety rule through the footplate geometry, and genuine airflow through an adjustable, lockable opening.
LockLatch® ships from our UK distribution centre in Penley, near Wrexham.
Shop LockLatch® now and secure your windows in the open position.
