Most sash window owners can name the fitch lock on the meeting rail and maybe the lifters on the bottom rail. Very few have heard of the third piece of hardware, the one that did its job in the photo below.
After an attempted break-in at a customer's home. The fitch lock tore out of the timber. The window stayed shut.
This window was forced hard enough to rip the lock clean out of the sash, screws and all. What stopped the intruder was a pair of window restrictors, sometimes called angle locks, fitted higher up the frame. They're small, they're discrete, and they're the reason the house stayed sealed.
What a restrictor actually is
A restrictor is a palm-sized device that limits how far a sash window's lower sash can travel. Ours are the Angel face fixed type: a spring loaded arm behind a slim brass faceplate, 86mm long and 16mm wide. One goes on each side of the window. When the sash rises and meets the arms, it stops. Press the small release and the arms fold away so the window opens fully. Close the window and the arms reset on their own. There is no key, which means there's no key to lose and nothing to forget at night.
Why it holds when a lock doesn't
The difference is in the fitting. A surface mounted lock hangs its whole strength on two screws driven into the face of the sash. Lever the sash hard enough and the screws pull through, which is exactly what happened in the photo above.
A restrictor is fitted the other way: the body sits in a small mortise cut into the timber, embedded in the frame itself. Only the faceplate shows. Force on the sash goes into the timber around the device, not into two screw threads. There's no housing to lever off and no fixing to tear free.
The body is mortised into the frame. Only the slim faceplate shows.
The paperwork behind the claims
We don't ask you to take any of this on trust. These devices carry lab results that very little window hardware sold in Australia can match:
- PAS 24:2016 enhanced security. A traditional timber sash window fitted with these devices passed the full PAS 24 test sequence at Wintech's UKAS accredited laboratory: manipulation tests, infill tests and mechanical loading. Report R17136 is here.
- 350N load capacity. Verified to BS EN 14351-1:2006 by Exova Warringtonfire, also UKAS accredited. That report is here.
- ASTM F2090. The window fall prevention standard written to protect young children, tested across the 2008, 2010, 2013 and 2017 versions.
The child safety side
That last standard is the other reason to fit restrictors. A window that only opens 150mm still airs the room, but a child can't fit through the gap. Flyscreens don't hold a child's weight, and a locked window doesn't stay locked through an Australian summer. Restrictors are the version of window safety that survives real life: automatic, keyless, and always re-engaged after the window closes.
One honest note: no device replaces supervision, and household members old enough should be shown how to release the restrictors in an emergency. The safety guide covers this in a page.
Fitting them
This is a fair Saturday morning job for anyone comfortable with a drill and chisel. Per window: mark your opening height above the closed bottom sash, cut a 57.5 x 12.5mm mortise 15mm deep on each side, screw the faceplates down, stick the buffer pads on, and test. About twenty minutes a window once you've done your first. The step by step instructions are here, and the dimensions drawing has every measurement if you're routing the mortises.
Where to get them
We stock the keyless auto reset restrictor in five finishes (polished brass, antique brass, polished chrome, satin chrome and white) at $24.95 each, and a lockable version with a child-proof key at $28.56. Each window needs a pair.
More on the security story, with photos from the break-in that opened this article: Sash Window Security Restrictors. For the family angle: Child Safe Sash Windows.