Understanding the Locking Mechanisms in uPVC Windows

How A Multi-Point Lock Works

Turn the handle on a modern uPVC window and a steel bar, the espagnolette, slides along the length of the sash. Fixed to that bar are cams, rollers or mushroom-headed studs that rotate into keeps fixed to the frame.

The important word is multi-point. A single-point lock engages once, usually in the middle, and the corners of the sash can be levered. A multi-point system engages at several places up the height of the sash, so there is no single spot to attack.

Mushroom-head cams are the ones worth having. As they rotate into the keep, the mushroom shape pulls the sash tighter into the frame rather than simply blocking it, which resists levering far better than a plain roller.

The Handle Is Usually The Weak Point

The mechanism can be excellent and the window still insecure if the handle is not lockable. A non-locking handle can be turned by anyone who reaches it, which matters if there is a letterbox, a cat flap or a pane that can be broken nearby.

Look for a key-locking handle with an internal locking pin that stops the spindle turning. Then have all your handles keyed alike, because a set of windows with six different keys ends up with every key left in the lock.

Internally Beaded Glazing

Beading is the strip that holds the glass in the frame. If it is on the outside, the glass can in principle be removed from outside by prising the beads off, with no noise and no broken glass.

Internally beaded windows put that strip inside the room, so the pane cannot be lifted out from the street. Every window we fit is internally beaded as standard, and if you have older externally beaded units it is worth knowing.

Standards Worth Asking For

• PAS 24. An enhanced security standard covering the whole window, tested against realistic attack methods. Ask whether the window is PAS 24 tested as a complete unit, not just the lock.
• Secured by Design. The police-backed accreditation scheme. Products meeting it have been through independent testing.
• Laminated glass. Worth specifying on accessible ground floor windows. It holds together when struck rather than falling out.
• Restrictors. Useful on upper floors where you want ventilation without an open window, and sensible where there are children.

Keeping Them Working

Almost every window lock failure we are called to is a maintenance issue, not a manufacturing one.

Twice a year, put a drop of light oil on the cams and the keeps, and check the handle screws are tight. If the handle is getting stiff, that is the mechanism telling you it needs lubricating before something breaks. A seized espagnolette usually means replacing the whole strip.

Clean the seals with a damp cloth and keep the drainage slots at the bottom of the frame clear. Blocked slots hold water in the frame, and that is what corrodes the mechanism from underneath.