A home boasting elegant sash windows is often admired for the defined period style that sash windows evoke. However, due to the age of sash window design, there are often common misconceptions that they are not as secure as newer style window designs. But sash windows have stood the test of time for a reason.
If you are thinking about installing restrictors on your windows to restrict how far your window is able to open, you will be pleased to know that it is an easy D.I.Y task that even beginners can do. Whether you want to childproof your sash windows or add some extra security to prevent intruders, our step-by-step guide on how to install a sash window restrictor is all you need.

Where should I fit a sash window restrictor?

Typically, sash restrictors are fitted 100mm above the mid rail, so that the window can only be opened by 100mm. 100mm is the industry standard fit as it is estimated that a baby could not fit through a 100mm opening and fall out the window. For customers that do not have children to safeguard, but are concerned about security, we would recommend fitting the restrictors directly above the mid rail, so that if the bottom sash is forced open by an intruder with a crowbar (for example), then the restrictors will prevent any further movement.

Are sash window restrictors childproof?

Yes, they sure are.  Unlike sash window locks, restrictors require a key to open the window and therefore ensure a childproof sash window.

Which sash window restrictors should I use?

There are a variety of sash restrictors on the market, all of which come with their own unique installation instructions.  It is very important that you purchase your restrictors from a reputable ironmongery supplier and avoid ones from sites like Amazon that can be flimsy and unreliable.  We would recommend going to Mighton or Reddiseals.

Some sash restrictors from these suppliers are easier to fit than others. Our preferred product is the MigStop from Mighton

Install a sash window restrictor in 5 easy steps:

This is a guide to fitting the MigStop restrictor from Mighton.
Parts list:


Close and lock sash before starting installation. Measure 100mm up from top of bottom sash and mark window frame as shown above.
Drill a 10mm diameter hole 18mm deep on the marked positions on the top sash.


Using a 6mm Allen key, screw the Insert Unit (A) into the holes on both sides of the top sash.
Attach Barrel Unit (E) into Insert Unit (A) using the Key (B) provided and lower the sash. Install the Strike Plate (C) where the Barrel Unit (E) meets the meeting rail using the Screws (D) provided.


Verify device operates correctly and window opening cannot exceed 100mm.

You can de-activate/activate the MigStop by removing/attaching the barrel unit with the key provided.  Make sure you keep the key in a safe place!

If you are looking to renovate your existing sash windows this year, or maybe you are considering sash windows for the first time, don’t forget we are always on the end of the line to chat through your questions and queries so don’t be afraid to give us a call on 020 3582 762, email or fill in our contact form and we will get back to you ASAP.

Contact the Wandsworth Sash Windows team

Talk to us – we can help with your bespoke window, door and joinery requirements. Call 02079247303 or email