The basics
What most window locks actually do
The little latch on top of the sash is doing more than you think, and less.
The sash lock on a double hung window
Most windows in Delaware homes are double hung, with an upper and a lower sash that slide past each other. Where the two sashes meet in the middle, a small lock is mounted on top of the lower sash, with a curved arm that rotates into a keeper on the upper sash. People often call it a crescent lock because of the shape of the arm.
That lock does two things. It stops the lower sash from being raised and the upper sash from being lowered, which keeps the window closed. And as the arm rotates, it pulls the two sashes toward each other and presses them together, which closes the gap between them and reduces drafts. A window that feels drafty in the middle often has a sash lock that is not pulling the sashes tight.
What a sash lock does not do is make the window strong. It is a small piece of hardware held by short screws into the sash. It stops a window from being casually opened from outside and it makes a quiet entry harder. It will not stop someone determined to force the window or break the glass. That is why window security usually combines a working sash lock with other measures, such as window stops, good lighting and landscaping that does not hide ground floor windows.
Problems
Why window locks stop working
- Sashes out of alignment. When the sashes do not meet evenly, the lock arm misses the keeper or catches only its edge. Worn balances, swollen wood and settling frames all cause this.
- Loose or stripped screws. Sash lock screws are short and set into narrow rails. They loosen with use, and in old wood or thin vinyl the holes strip. A loose lock wobbles and does not hold.
- Paint and grime. In older homes, sash locks are often painted over, sometimes several times. Paint jams the arm and fills the keeper.
- Broken or missing hardware. Cast metal and plastic locks crack, and some windows have simply lost their locks over the years.
- Worn window balances. The springs or weights that hold a sash up can fail, letting the sash drop or ride unevenly, which throws off the lock.
- Replacement windows with proprietary locks. Many modern vinyl windows use locks designed for that manufacturer. When they break, the replacement has to match the window.
Types
Window locks by window type
Double hung and single hung windows use sash locks, sometimes two on wider windows. Keyed sash locks are available and require a key to unlock. Window stops, also called vent stops or sash stops, mount in the side track and allow the lower sash to open only a few inches, which lets air in while keeping the opening too small to climb through. They can be released from inside to open the window fully.
Sliding windows, where one panel moves sideways, usually have a latch on the moving panel that catches the frame. Like sliding doors, the moving panel can sometimes be lifted out of its track. Track stops, which clamp into the track, and pins through both panels make sliders harder to open or lift from outside.
Casement windows, which swing outward with a crank, usually lock with one or more latches operated by a handle on the frame. On larger casements, a single handle may operate several locking points along the edge. Because they seal tightly when locked, casements are naturally harder to open from outside than many other window types, but only when every locking point engages.
Awning and hopper windows hinge at the top or bottom. They are common in basements and bathrooms. Their latches are usually simple, and basement hoppers at ground level deserve attention, because they are low, often hidden and sometimes left unlatched for months.
Storm windows on older homes have their own small latches. They mainly hold the storm panels in position and add a little resistance, but the main window lock still does the real work.
Older wood windows deserve patience
Original wood windows in older Delaware homes are often better built than people expect, with thick sashes, solid hardware and frames that have lasted a century. Their locks are usually repairable. The challenges are layers of paint, sashes that have been painted to the frame, sash cords or weights that no longer balance the window, and screw holes that have been reused so many times they no longer hold anything.
We approach these windows carefully. Cutting through paint along the lock and keeper, removing the hardware, cleaning it and reinstalling it with filled and redrilled screw holes brings many original locks back to life. Where the original lock is cracked, a replacement in a similar style keeps the look of the window. If the sash itself will not move because it has been painted shut, we point that out, since a window that cannot open is a problem for ventilation and escape as much as for security.
Historic homes sometimes have rules about changing visible hardware. If your home is in a historic district, check before changing anything visible from outside. Most window locks are on the inside and are not affected, but it is worth knowing.
Safety first
Every bedroom needs a window that opens
A lock that traps people inside is worse than no lock at all.
In a fire, a bedroom window may be the only way out. Fire safety guidance generally calls for every sleeping room to have a way to escape other than the door, and in many homes that is a window. Anything we add to a bedroom window has to keep that window easy to open from inside, quickly, in the dark and in smoke, by everyone who sleeps in that room.
That affects our recommendations. We generally avoid keyed locks on windows that serve as escape routes. If a keyed lock is used, the key needs to stay at the window, which undercuts the purpose. Window stops on bedroom windows must release easily by hand. Security bars or grilles on bedroom windows should have a quick release mechanism that works from inside.
Basement bedrooms deserve special attention. Some basement windows are too small or too high to serve as a practical exit. If a basement room is used for sleeping, it is worth checking whether it has a real way out.
If you are not sure how the rules for your home apply, your local building or fire official can advise. Our job is to make sure the hardware we install never becomes the reason someone could not get out.
Children
Window locks, stops and young children
Families with young children face a different window question: how to stop a child from opening a window wide enough to fall. Window screens are not designed to hold a child's weight, and many falls happen through screened windows.
Window opening control devices limit how far a window can open, commonly to a few inches, while still allowing an adult to release them for a full opening in an emergency. Window stops on double hung windows serve a similar purpose. Moving furniture away from windows so children cannot climb to them is just as important as any hardware.
The same safety principle applies. An adult must be able to open the window fully in an emergency, quickly and without tools. We choose devices that meet both needs and show the adults in the household how to release them.
As children grow and rooms change, revisit the setup. A device that made sense in a toddler's room may need to change when that room becomes a teenager's bedroom.
How it works
What happens during a window lock visit
We walk through the house with you, window by window, starting with ground floor windows and windows reachable from porches, decks and garage roofs. For each one, we check whether the lock engages fully, whether the sashes or panels are aligned, and whether the window serves as an escape route.
Where a sash lock is loose, we tighten or reset it, using longer screws or filled holes where the old ones have stripped. Where a lock is painted shut, we loosen it, clean it and restore its movement. Where sashes are misaligned, we adjust the lock and keeper so they meet properly, and if the sash balance is failing, we tell you so it can be repaired.
Where hardware is broken or missing, we replace it with a lock that fits the window. For replacement windows with manufacturer specific locks, we identify the window and source the matching part where possible.
We add window stops, track stops or pins where they make sense, and opening control devices in children's rooms if you want them. We test every lock and every stop, and we confirm that escape windows open quickly from inside.
Keeping window locks working through the year
Window locks need very little care, but a short check twice a year catches most problems early. In spring and fall, walk through the house and operate every window lock. Each one should turn smoothly, pull the sashes together and stop firmly. If a lock feels loose, tighten its screws gently. If it catches or needs pressure on the sash to close, the sashes have moved and the keeper may need adjusting.
Clean the tracks on sliding windows and the sills on double hung windows. Dirt and debris in the track lift a sliding panel and make its latch miss. A vacuum and a damp cloth do the job.
Check window stops and child safety devices too. Make sure they still hold and still release easily, and that everyone who might need to open a window in an emergency knows how. A device that only one person in the house can operate is not doing its job.
After a storm or a long stretch of damp weather, recheck windows that are known to stick. Wood sashes swell, and a lock that closed yesterday may not close today. Forcing a lock against a swollen sash can crack the lock or pull out its screws, so if a window will not lock, leave it closed and have it looked at rather than forcing it.
Options
Window lock options compared
| Window | Common issue | What usually helps |
|---|---|---|
| Double hung, ground floor | Loose or misaligned sash lock | Reset lock and keeper, add window stops for ventilation |
| Double hung, older home | Painted over or broken lock | Loosen or replace the lock, secure with longer screws |
| Sliding window | Panel can be lifted or latch misses | Adjust latch, add track stops or pins |
| Casement window | One locking point not engaging | Adjust keepers and handle, replace worn latch |
| Basement hopper | Left unlatched, hidden from view | Repair latch, consider a secondary lock that still allows exit |
| Child's bedroom | Fall risk | Opening control devices with an adult release |
Beyond the lock
Making windows a less attractive way in
Window locks work best as part of a wider picture. Most people trying to enter a home unseen look for an easy, hidden opening. Anything that makes a window more visible, more obviously secured or more awkward to reach helps.
Trim shrubs and bushes below ground floor windows so the windows can be seen from the street and from neighbors' homes. Add lighting near windows at the back and sides of the house, where darkness gives cover. Keep ladders, trash bins and outdoor furniture away from windows and from anything that gives access to upper floor windows, such as a porch roof.
Lock windows when you leave the house, including upstairs windows that you might assume are out of reach. Close and lock basement windows, which are often forgotten after being opened for air. Consider security film on glass near door locks or on vulnerable ground floor windows, which holds broken glass together and slows entry.
For doors near windows, remember that a window next to a door can let someone reach in to a thumb turn. Our deadbolt installation page covers options for doors with glass nearby.
Avoid these
Window lock mistakes
- Keyed locks on escape windows. A key that must be found in a fire is a key that may not be found.
- Nailing or screwing windows shut. It blocks escape and damages the window. Use removable stops instead.
- Assuming upstairs windows are safe. Porch roofs, garage roofs and decks put many upper windows within reach.
- Relying on screens to protect children. Screens keep insects out, not children in.
- Ignoring a drafty window. A sash lock that does not pull the sashes together wastes energy and holds poorly.
- Leaving basement windows unlatched. They are low, hidden and easy to forget.
Local factors
Windows in New Castle and Kent homes
Old wood sashes, new vinyl and everything between.
Older homes in Wilmington, New Castle, Elsmere and downtown Dover often have original wood sash windows with sash locks painted over many times and sashes that have shifted. Freeing and resetting those locks, and adding stops, is common work there.
Newer homes in Middletown, Bear, Smyrna and Camden usually have vinyl windows with manufacturer specific locks. Those locks rarely fail early, but when they do, matching the part to the window matters.
Delaware's humidity swells wood sashes in summer and shrinks them in winter, so a window that locks easily in one season may resist in the other. Adjusting the keeper with that movement in mind helps the lock work year round.
Questions
Frequently asked
My window lock will not close. What is wrong?
Usually the sashes are not lined up, so the lock arm misses the keeper. Paint, loose screws and worn balances are other common causes. Adjusting the lock and keeper often solves it.
Should I put keyed locks on my windows?
Not on windows that serve as escape routes, especially in bedrooms. Keyed locks can make sense on windows that are never used for escape, but window stops that release by hand are usually a better choice.
What is a window stop?
A device mounted in the window track that lets the window open only a few inches for air. It can be released from inside to open the window fully.
Can you fix the lock on my vinyl replacement window?
Often. Many vinyl windows use manufacturer specific locks, so we identify the window and match the part. Sometimes an adjustment solves the problem without new hardware.
How do I keep my child from opening a window too far?
Window opening control devices or stops limit the opening while letting an adult release them for full opening in an emergency. Move furniture away from windows as well.
Can a sliding window be lifted out of its track?
Some can. Track stops, pins through both panels and adjustments to reduce the space above the panel make that much harder.
My window is drafty in the middle. Is that a lock problem?
Often, yes. A sash lock that does not pull the sashes together leaves a gap. Adjusting or replacing the lock usually improves the seal.
Do you replace window glass?
No. We handle window locks, latches and stops. Glass and full window replacement belong to a window or glass company.
Windows that will not lock?
Call and we will fix the locks, add stops where they help and keep every escape window easy to open.