Someone tried to get into a house through a ground floor sash window. They got the bottom sash open a few centimetres, forced it, and the window still would not let them in. The surface lock tore clean out of the timber, but the sash barely moved. Here is what happened, why it happened, and what it tells you about securing your own old windows.
What the burglar did
The window was a standard double hung sash on the ground floor, the kind you find on the front of half the older houses in the country. It had a small surface mounted lock screwed to the top of the bottom sash, the sort that comes fitted as standard on a lot of windows. It also had a pair of restrictors fitted into the sides of the frame.
The person forcing the window went at the bottom sash first. A bit of leverage on a sash that only has short screws holding the lock will usually pop it open. That is exactly what they got: the lock let go. But the sash only travelled a short distance before it stopped hard and would not go any further. Whoever it was gave up and left. The frame took some damage around the lock, the timber was scarred, but the opening never got wide enough for a person to climb through.
Why the surface lock failed
A surface mounted lock does one job reasonably well and one job badly. It holds the two sashes together so the window does not rattle or drift open, and it stops a casual push from outside. What it cannot do is resist someone deliberately levering the sash.
The reason is simple. A surface lock is held on by short screws that bite into the face of the timber. When you lever the sash, all the force goes into those few screws, and they are pulling straight out of the grain. Old softwood that has had a century of paint and weather is not the strongest thing to screw into. Add a bit of rot near the meeting rail and the lock has almost nothing to hold onto. It is not a fault in the lock so much as the way it is fixed. Pull hard enough in the wrong direction and it comes away with a chunk of paint and timber attached.
Why the restrictors held
The restrictors were a different story, because of how they fit. A rebated restrictor sits in a housing cut into the side of the frame and the edge of the sash, so the load is spread through the timber rather than hanging off a couple of surface screws. When the sash was forced, it slid up until the restrictor pins engaged, and then it stopped. The force was trying to shear the pins and push against the sides of the housing, which is a much harder thing to beat than pulling screws straight out of a face.
That is the whole point of a restrictor. It is not there to make the window impossible to open. It is there to limit how far the window travels, so even if the main lock is defeated the gap never opens up enough to be useful. On this window the lock was the weak link and the restrictors were the backstop, and the backstop did its job.
You can read more about how restrictors work and where they suit an old window in our guide to window restrictors and the sash window upgrade almost nobody knows about.
The independent testing evidence
It is easy to tell a good story about one window and leave it there. What matters more is whether the hardware performs when someone tests it properly, over and over, rather than in a single lucky incident.
The restrictors we supply have been through independent testing, and the test reports are available on the sash window security restrictors page so you can read them yourself rather than take our word for it. We are not going to make claims about what any particular standard means for your house or your insurance, because that depends on your situation and is not something a blog post should decide for you. What we can say is that the reports exist, they are public, and you can judge them on their merits.
Securing your own windows
If you have old sash windows on the ground floor, or anywhere a person could reach, here is a sensible way to think about it.
First, do not rely on a single surface lock as your only line of defence. It is fine as the everyday catch that holds the window shut, but treat it as the thing that gets beaten, not the thing that saves you.
Second, fit restrictors that seat into the timber rather than sit on top of it. The fixing method is what does the work. A restrictor that spreads load through a housing in the frame will hold long after a face screwed lock has let go.
Third, think about the whole window. A restrictor is one piece. Lifters, locks and restrictors all matter, and it helps to have them working together rather than a good restrictor next to a lock that is loose in rotten timber. If the timber around your existing hardware is soft, that is worth sorting out at the same time, because no fixing holds well in rot.
When you are ready to fit them, the sash window restrictor (angle lock, no key) is the version most people fit themselves with a screwdriver and a bit of care. If you also want to tidy up the everyday hardware while you are at it, the hardware bundle pairs lifters with a sash lock so the visible fittings match.
FAQ
Will a restrictor stop a window opening at all?
No, and it is not meant to. A restrictor limits how far the sash travels. You can still open the window for airflow up to the limit, and on most fittings you can release it fully from inside when you want to. The point is that the gap stays small unless you choose otherwise.
Are surface locks a waste of time then?
No. A surface lock is a good everyday catch that holds the window shut and stops a casual push. It just should not be the only thing standing between an intruder and your house. Pair it with restrictors and each part does what it is good at.
Can I fit restrictors myself?
Most people can. The angle lock version fits with a screwdriver once you have marked the position and drilled the pilot holes. The main thing is to seat it into sound timber, so if the wood is soft or rotten near the fixing point, deal with that first.
Do restrictors work on any sash window?
They suit most standard double hung timber sash windows. Very unusual sizes or badly out of square frames can need a bit of extra fitting work, but the principle holds for the common cases. If you are unsure about your window, measure it and check the product page before ordering.
Where can I see the test reports?
They are published on the sash window security restrictors page. You can read the independent testing there and make your own judgement.