uPVC is the dominant window material in UK homes, installed in an estimated 85 percent of all replacement windows since the 1980s. Every uPVC window comes with a multipoint locking mechanism, typically an espagnolette, that locks the window firmly shut. Some have a night vent position that holds the window open by approximately 25mm, but this is not secure. It can be prised open with a flat tool and does not meet Secured by Design standards. The result is that millions of UK homeowners face a binary choice on warm evenings: locked shut and stuffy, or open and insecure. LockLatch eliminates that choice by locking the window in the open position at an adjustable gap of 9 to 17 centimetres, secured with a key-operated pin.
The Problem with Night Vent Positions
The night vent is designed to allow background airflow while maintaining a degree of security. In practice, it does neither well. The 25mm gap provides negligible ventilation. A kitchen producing steam, a bedroom on a July evening, a bathroom after a shower: 25mm is not enough. And the security it provides is questionable. The gap allows a tool to be inserted to apply leverage, and the locking mechanism in the vent position is weaker than in the fully closed position.
Trickle vents, now mandatory in new builds under Part F of the Building Regulations, provide passive airflow through small slots in the frame. They help with background ventilation and condensation prevention but cannot replicate the air exchange of an open window. Millions of older uPVC windows lack them entirely.
What uPVC Window Locks Actually Do
Three types of locking mechanism are fitted to UK uPVC windows. Espagnolette locks are the current standard: a central gearbox operated by the handle engages mushroom cams into locking strips along the frame edges. Cockspur locks are older (pre-2000s): the handle latches onto a fixed strike on the frame. Shootbolt locks are the premium option: bolts extend from the sash into the frame top and bottom. All three lock the window shut. None allow secure ventilation in an open position.
Adding a Ventilation Lock to uPVC Windows
LockLatch fits any uPVC window with four holes, fixed using rivets (the same method used on aluminium windows). It does not replace the existing espagnolette or shootbolt mechanism. It supplements it. When the homeowner wants ventilation, the existing lock is disengaged and the window is opened to the desired width. LockLatch then locks the window at that position with an adjustable C304 stainless steel arm and a lockable pin. The gap can be set anywhere from 9 to 17 centimetres.
For child safety compliance, MiniLatch restricts the gap to 4.5 to 8 centimetres, within the 100mm maximum required by UK building regulations. Installation takes 15 minutes with a drill and rivet gun. No modification to the window mechanism and no tradesman required.
Can You Add Extra Locks to uPVC Windows
Yes, and there are good reasons to do so. The factory-fitted locking mechanism on a uPVC window is designed to secure the window in the closed position. It does this effectively when it is working correctly. But uPVC locks age. After 10 to 15 years, gearboxes seize, handles become stiff, mushroom cams no longer engage cleanly with locking strips and the mechanism provides less security than it did when new. A full gearbox replacement costs approximately 175 pounds per window including parts, labour and VAT.
Adding a supplementary lock like LockLatch does not strengthen the closed-window security of the existing mechanism. What it does is extend security to the open position, which the existing mechanism cannot. LockLatch works alongside the espagnolette rather than replacing it. When the window is closed, the espagnolette does its job. When the window is open for ventilation, LockLatch does its job.
uPVC Windows and Child Safety
UK Building Regulations require windows with sills below 1,100mm above floor level to have restrictors limiting the opening to 100mm maximum in premises where children may be present. Many older uPVC windows were installed before this regulation was tightened and do not have built-in restrictors. Retrofitting a restrictor is the standard solution.
MiniLatch adjusts from 4.5 to 8 centimetres and sits within the 100mm child safety requirement. Note that the effective opening is narrower than the nominal range because the footplates mount mid-frame rather than at the edge, which reduces the practical gap by around 3 to 4 centimetres. For a child safety restrictor this is exactly what is wanted. For airflow, the standard LockLatch at 9 to 17 centimetres is the better fit in rooms without child safety requirements.
The Summer Ventilation Challenge
UK summers are getting warmer. The Met Office recorded the hottest year on record in 2023 and subsequent years have continued the trend. Homes built with uPVC double glazing in the 1990s and 2000s were designed to retain heat, not to release it. They are highly insulated boxes that become uncomfortable when temperatures climb above 25 degrees. The only effective cooling for most of these homes is opening windows. Air conditioning remains rare in UK residential properties.
A window locked open at 9 to 17 centimetres provides substantial airflow, enough to create a cross-breeze through a room when windows on opposite walls are both fitted with LockLatch. The adjustability means the homeowner can set a narrower gap on ground-floor windows facing a public footpath and a wider gap on upper-floor windows where security risk is lower.
How It Compares to Other Options
Sash jammers lock the window shut. They provide zero ventilation. Cable restrictors limit the opening to approximately 100mm, which is better than a night vent but still limited and offers no adjustability or rigidity. Surface-fixed ventilation locks designed for timber windows have mixed results on uPVC. Most budget restrictors are not key-lockable and their fixed cable length offers no adjustability.
LockLatch is the only product that combines adjustable opening width, key-operated locking, stainless steel construction and a lifetime guarantee across all uPVC window types: casement, tilt-and-turn, side-hung and top-hung.
Insurance and Security
Most UK insurers require key-operated locks on ground-floor and accessible windows. A window left on the night vent position may not satisfy this requirement. LockLatch is key-operated and physically locks the window at its set position. Thirty percent of UK burglaries involve entry through a window, and according to Metropolitan Police data, only 6.3 percent of those involve breaking glass. The rest exploit unlocked or poorly secured windows. A window locked open with LockLatch is secured. A window on a night vent is not.
LockLatch ships from our distribution centres in the UK and South Africa.
Shop LockLatch now and ventilate your uPVC windows securely.
