How to Fit a Sash Jammer to uPVC Doors, Windows and Letterboxes

Sash jammers are one of the cheapest ways to add a second lock to a uPVC door. You can fit them yourself with a drill and a screwdriver. We sold over 680 of our Home Secure sash jammers online last year, with customers buying about four at a time on average. Here's where they work, how many you need and how to fit them.

What a sash jammer does, and where it works

A sash jammer is a small metal lock that fixes to the frame on the inside. When you swing its arm across, it sits over the edge of the door or window (the "sash"), so the sash can't move into the room. Swing it back and the door opens as normal.

Because it holds the sash from the inside, a sash jammer only works on things that open inwards:

• Front and back doors that open into the house.
• Inward-opening French or patio doors.
• The inside flap of a letterbox. Two jammers hold it shut, so nothing can be pushed through or fished out. That's our "letterbox lock".
• Inward-opening windows, such as tilt and turn.

If your window or door opens outwards, a sash jammer can't stop it opening. For those, use a locking window handle or a window restrictor.

How many sash jammers do you need?

Doing a door? You'll need two

One at the top and one at the bottom of the opening edge. Two on the inside flap make a letterbox lock. £3.99.

View sash jammers →

What's in the pack, and what you need

• In the pack: the jammer (60mm long, with a 75mm arm), 3 different-sized buttons to suit the depth of your frame, 2 base packers, and two 32mm self-tapping screws.
• You'll need: a drill with a 2mm bit, a cross-head screwdriver and a pencil.
• Maybe: jack nuts (sold separately) and a 9.5mm drill bit, if your frame has no steel reinforcement inside. You'll find out at step 3.

How to fit a sash jammer

1. Position it. With the door or window shut, hold the jammer on the inside face of the frame, next to the opening edge. Swing the arm across: it should sit over the sash without forcing. Then open and close the door to check it doesn't touch the jammer body. Mark the two screw holes.
2. Get the fit right. If the arm is loose or tight over the sash, change the button underneath it for one of the other sizes. If the jammer needs raising, add a base packer.
3. Drill 2mm pilot holes, using the jammer as a guide.
   • The drill meets hard resistance partway in: there's steel reinforcement in the frame. Use the screws supplied.
   • The drill goes through easily: there's no steel, and screws won't hold well. Open the holes up to 9.5mm and fit jack nuts instead.
4. Screw it on. Tighten the screws firmly, but stop before they strip the uPVC.
5. Test it. Swing the arm over and try to open the door or window: it shouldn't move. Swing it back and check it opens normally.

Fit the second jammer the same way. On a door, fit one near the top and one near the bottom of the opening edge.

Screws won't tighten? The hole has worn or there's no steel behind it. See our guide to screws for uPVC for the fix.

Drill went straight through?

There's no steel in the frame, so use jack nuts instead of the screws supplied. £0.60.

View jack nuts →

Using sash jammers day to day

• Swing them on at night and when you go away. They're a second lock, not a replacement for locking the door properly.
• Swing them off before anyone tries to open the door, or they'll be pushing against the jammer.
• On a letterbox, no post can come through while the jammers are on, so swing them off in the morning.
• Keep a way out. Make sure everyone in the house knows how to release them quickly in an emergency.

Sash jammers and the rest of your door security

A sash jammer adds an extra fixing point, but the main lock still matters most. If your door has an older euro cylinder, the most important upgrade is a TS007 3-star anti-snap cylinder. For the letterbox, see our guide to preventing letterbox burglary.

Need help?

Not sure if a sash jammer will fit? Send a photo of the inside of your door or window frame to info@homesecureshop.co.uk, or call us on 0151 521 8089.