07 November 2025
In this guide from SashWise, we will walk you through the main lock and fastener types for both traditional timber sash and casement windows. We will explain how they work and what to consider when choosing window locks.
Traditional timber sash and casement windows form an integral architectural feature to many period homes. Their distinct design makes them highly desirable, but like all opening windows they can be a weak point if not properly secured.
Security: There are approximately 50,000 burglaries in London per year, of which it is estimated 30% involve entry via a window. Burglars often target windows because they are typically less fortified than doors and can be easier to manipulate. Quality window locks form both a physical and visual deterrent, giving you and your family peace of mind.
Safety: Certain window locks can limit how far a window can open which can be very important for child safety. They also allow the window to be partly open to provide ventilation whilst remaining secure.
Performance: Correctly functioning fasteners make the window more airtight thereby reducing draughts and unwanted rattling.
Longevity: Having window locks and fasteners helps reduce frame twist and sash warping over time.
There is a misunderstanding amongst many homeowners that because their timber windows have fasteners, they are adequately secure. Unfortunately, this is often not the case.
The purpose of a window fasteners is to either clasp the casement sash within the window frame. Or in the case of timber box sash windows, to hug the two vertically sliding sashes together. Their function being to assist making the window more airtight. In the vast majority of cases window fasteners are non-locking and therefore deemed not to be security locks.
In contrast the primary purpose of a window lock is to prevent or restrict the ability of the window to be opened. Window locks in the most part are key operated and therefore classified as 'security locks', and as such are recommended by household insurance companies.
Traditional fastener suitable for double glazed timber windows. Designed to pull, lift and align the meeting rails of the sashes together.
A locking version is available which incorporates a a small grub screw that can be raised using a key to stop the arm of the fastener from swinging open. This can be fiddly to operate and not very strong, so offers limited security.
A traditional style fastener available in a range of finishes. excellent at pulling the meeting rails of the sashes together for airtightness. A locking version is available byt forced entry would rely on the strength of the screws holding the fastener in place.
Fitted as a pair, the lock fixings are screwed directly into either side of the upper sash frame. Usually sited 10cm above the meeting rail, they allow the sash window to be partly open for ventilation whilst remaining secure. Alternatively, the barrels can be complexity removed using a key to allow the window to be fully opened.
Secure sash stop locks are easy to use and being key operated they are insurance company compliant. They offer a heavy-duty security solution at the same time not detracting from the beauty of the traditional looking sash window.
Fits through the meeting rail of both sashes securing them together to prevent opening. They are very strong but do not allow for partial ventilation and they can hinder any draught excluder that runs along the meeting rails.
They are difficult to use as trying to align the fixings for the screw can be challenging.
A classically designed traditional fitting available in a range of finishes. Prevents the sash being opened beyond the stop so excellent for ventilation. Requires a large rebate into the side of the sash frame which is not always practical, particulalry when retro-fitting into existing windows. Can be awkward to use.
Primary function is to act as a handle to open and close the casement sash and to hold the sash tight into the window frame when shut for airtightness. Available in a wide range of styles and finishes to compliment the design of the window. Locking versions are available which are both key operated and easy to use, but do not offer a high level of security.
Works in conjunction with a traditional casement stay and therefore the least visually intrusive of all of the casement locks. Compatible with a wide range of different designs of casement stays.
Can lock the stay in both a closed and partially open position, so facilitates ventilation whilst remaining secure. Easy to use and install, key operated so insurance company compliant.
The lock pivots onto the keep when the window is closed and secured in place using a key. Very strong and often used in conjunction with traditional casement window fittings when an additional level of security is required.
Insurance company compliant but cannot be used to secure the window partially open for ventilation. They are designed purely for strength rather than any aesthetic quality so visually detract from the look of a traditional timber casement window.
Sole purpose is to provide a child resistant locking system to prevent the window from being opened beyond a certain point.
A high performance locking system which is exceptionally strong, similar to those used in doors. Window handle drives multiple concealed hooks into the window frame. Meets the security requirements of current Building Regulations for new builds. Typically used only in modern timber windows as it needs a large frame thickness to accommodate the locking system.
Aesthetics vs. Insurance Reality: Fitting window locks to traditional timber windows does not have to be a trade-off between security and design. There are many window locks that are discreet and can even compliment the period features of the window, whilst at the same time complying with building insurance requirements.
Noise Pollution & Air Leakage: Crude or loose-fitting window fasteners allow sashes to vibrate. Choose window ironmongery that positively pulls the sashes together or into the window frame.
Ease of Use: Window locks and fasteners that are difficult to operate will by default not be used which means the window will remain unsecure and vulnerable to intrusion.
Child Safety & Ventilation: Sash Stop Locks and Casement Locking Stay Pins allow safe and secure 'partial open' ventilation whilst at the same time remaining secure.
Building Control: For new-build compliance and high-risk locations look for locks tested to PAS 24 /Secured by Design or equivalent national schemes.
Securing your timber windows does not need to be over complicated. The right lock and fastener will keep your home safe while maintaining the look and smooth operation of your windows. At SashWise we supply and fit a wide range of window locks and fasteners and we will be more than happy to advise you on the best solution for your individual security requirements, providing peace of mind for both you and your family.
