What do I need, a Rim Lock or Mortice Latch?

Author: Carl Benson

Carl is the founder of Suffolk Latch Company, with a background in engineering and over 20 years’ experience in home hardware. He works closely with suppliers and designers alike to develop quality ironmongery that stands the test of time. Read my full bio.

Table of Contents

• Introduction
• What’s the difference between a rim lock and a mortice latch?
• Rim Locks: Pros and Cons
• Mortice Latches: Pros and Cons
• Which is more secure?
• Conclusion
• Frequently Asked Questions

What do I need, a Rim Lock or Mortice Latch?

Introduction

When upgrading or restoring a door, a common question is whether to use a rim lock or a mortice lock. Both will keep your door closed, but they differ in how they are fitted and how they function. In this guide, we explain in practical terms the differences between rim locks and mortice latches, their pros and cons, and how to choose the right option for your needs.

What’s the difference between a rim lock and a mortice latch?

Rim Lock: A rim lock is a locking mechanism that mounts on the surface of the door, usually the inside face of an internal door. The lock body is a visible box on the door, typically with a keyhole and often paired with a surface-mounted keeper. This traditional style has been used since Victorian and Edwardian times, giving a door a period traditional appeal. The latch or lock bolt extends from the rim lock into a keeper on the door frame. Because it’s surface-mounted, a rim lock is ideal for older, thinner doors or where you want to avoid cutting into the door.

Mortice Latch: A mortice latch, sometimes just called a tubular latch, or if it includes a locking bolt, a mortice lock or sash lock, is fitted inside the door itself. A rectangular pocket (mortice) is cut into the edge of the door to recess the latch mechanism. From the outside, you only see the forends plate on the door’s edge and the spindle hole for a handle or knob. This gives a sleeker, modern look with no bulky box on the door.

In summary: A rim lock sits on the door’s surface and is visible, often providing a traditional look, whereas a mortice latch is embedded within the door, hidden from view for a cleaner finish. The choice can affect both the look of your door and how you install the hardware.

For a deeper dive into the history and types of rim locks, see our separate article: What is a Rim Lock

Rim Locks: Pros and Cons

Rim locks have specific advantages that make them suitable for certain situations, as well as some limitations. Here are the key pros and cons of choosing a rim lock:

Pros:

• Vintage Style & Character: Rim locks lend an authentic period appearance to a door. The visible lock box and old-fashioned key add rustic traditional appeal, making them ideal for cottages, historic homes, or anyone going for a traditional look. We showcase some classic examples in our design blog.
• Easy Installation due to being surface-mounted: Fitting a rim lock is relatively straightforward. It screws onto the door surface, so you don’t need to cut a deep pocket into the door. This is especially useful for thin or fragile doors that cannot be morticed without splitting. A rim lock can often be installed with basic tools, making it a convenient DIY job.
• Suitable for Problem Doors: Because they are surface-mounted, rim locks can be a good solution for doors that don’t have existing cut-outs or have non-standard sizes. They can also cover up old keyholes or damage on a door with their large lock body.

Cons:

• Lower Security: Rim locks are generally not as secure as modern mortice locks. The lock is attached to the surface with screws, which can make it easier to force open. For this reason, rim locks are not recommended for external doors as the primary lock. Most home insurance policies in the UK insist on a certified 5 lever locking systems on external doors.
• Limited Use for Bathrooms: Traditional rim locks usually cannot be opened from the outside. If used on a bathroom or WC door, there’s typically no emergency release if someone inside is incapacitated. Modern bathroom locks or a mortice bathroom latch with an external turn-release are safer for bathrooms. With new builds external release mechanisms are now a regulatory requirement.
• One-Sided/Handing Issues: The rim lock’s design means it only fits on one side of the door, the side that opens towards you. You usually can’t mount it on the outward-opening side of a door. Also, many rim locks are handed. For more detail on this, see our article Are Rim Locks Reversible?, which explains how to check handing.
• Bulkier Appearance: While period-appropriate to some, the visible box of a rim lock might look bulky or old-fashioned in a modern interior. It protrudes on the inside face of the door, which could be a drawback if you prefer a streamlined look.

In short, rim locks are best suited for internal doors where security is not the primary concern. They are not ideal for high-security needs or very modern design schemes.

Mortice Latches: Pros and Cons

Mortice latches and mortice locks are the modern standard for most doors, offering a different set of benefits and considerations:

Pros:

• Clean Look & Versatility: Because the mechanism is hidden inside the door, mortice latches give a clean, uncluttered appearance. You can use almost any style of door handle or knob on a morticed latch, maintaining a uniform design across your home. Whether you prefer lever handles, mortice door knobs, or a thumbturn for bathrooms, a compatible mortice latch or lock is available. If you’re exploring door knob options, our guide  might be helpful.
• Works on Either Side otherwise Reversible: Mortice latches are typically reversible or non-handed. The latch bolt can usually be flipped to suit left-hand or right-hand doors. This means one standard mortice latch can be fitted on doors opening in either direction, giving more flexibility than a rim lock.
• Range of Functions: There is a wide range of mortice mechanisms to choose from. Tubular latches provide simple latching for internal doors that don’t need a key. Sash locks (mortice locks with latch deadbolt) allow locking. Dead locks, just a key-operated bolt, no latch, are often used as a second lock on external doors. You can select anything from a basic latch to a high-security 5-lever lock or even modern . In other words, mortice fittings can cover everything from simple privacy needs to full security, all within the door.
• Better Security Options: A good mortice lock offers higher security than a rim lock. Because it’s embedded in the door and can engage a sturdy keep in the frame, it’s harder to force open. High-quality mortice locks have multiple levers or cylinders with anti-pick features. For external doors, a British Standard-rated mortice lock is often required – these locks provide strong resistance to drilling and picking, far beyond what a basic rim lock can do.
• Widely Used Standard: Mortice latches and locks are the standard in most UK homes today. This means replacement parts and sizes are widely available. If you ever need to replace or upgrade, you’ll find it easier to source a new mortice latch/lock that fits the existing cut-out than to replace a specific rim lock.

Cons:

• More Complex Installation: Fitting a mortice latch requires cutting into the door. You or your joiner will need the correct tools to cut out a precise pocket in the edge of the door to house the lock case and cut out a hole for the striker plate, this job requires proper tools and some skill to do neatly. If it’s not done correctly, the latch may misalign, or the door could be damaged. In many cases, hiring a professional carpenter or locksmith is wise, especially for installing mortice locks on valuable doors.
• Not Ideal for Thin or Old Doors: Morticing into a very thin or fragile door can be impractical. If the door stile (edge) isn’t thick enough, there’s simply not enough wood to safely fit the lock. Old panel doors with narrow rails or glass panels may not accommodate a standard mortice latch without modifications. In such scenarios, a surface-mounted rim lock/latch might be the only option.
• Time and Effort: Even for a skilled person, installing a mortice mechanism takes more time and effort than screwing on a rim lock. There’s measuring, drilling, chiselling, and fitting of both the lock and the striking plate on the frame.
• Hidden Mechanism: While being hidden is usually a positive, it also means if something goes wrong internally while the door is in the locked position, you may find yourself with no choice but to force the door open to replace it. In contrast, with a rim lock, you can typically remove the entire mechanism because all the fixings are accessible from the surface.

In summary, mortice latches/locks are versatile and generally more secure, making them suitable for most modern applications. Just be prepared for a more involved installation process and ensure your door can accommodate the lock. Once installed, they provide a neat look and reliable function, from basic latching to high-security locking.

Which is more secure?

Mortice locks are usually more secure than rim locks. The reason is largely due to their construction and installation:

A rim lock is mounted on the surface with screws, so it is inherently more exposed. A potential intruder can see the lock and may target its screws or try to pry it off. Many traditional rim locks also use simpler internal mechanisms (older lever or warded locks) that are easier to pick. Some common rim locks can be slipped open with the right method unless they have additional security features. For these reasons, rim locks are generally advised only for internal doors or as secondary locks. If you do use one on an exterior door it should ideally be supplemented with an insurance compliant lock.

A mortice lock, being buried inside the door, is harder to attack directly. Only the keyhole is visible, so there are no exposed screws to tamper with on the outside. Mortice locks designed for external doors, like 5-lever British Standard locks or euro-profile cylinder mortice locks, have robust metal cases, anti-saw bolts, and anti-pick mechanisms. When fitted properly into a solid door and frame, they provide a high level of security. This is why insurers and locksmiths will nearly always recommend a mortice deadlock for front and back doors.

However, security ultimately depends on the quality of the specific product and the quality of installation. A cheap, badly fitted mortice lock might fail or be easily bypassed, whereas a well-made rim lock installed correctly could keep a door secure for low-risk situations. Always consider the context: for an external entry door, choose a lock that meets security standards (BS3621 or equivalent) – this will almost always be a mortice lock rather than a rim lock. For internal doors, security is less critical, so a rim lock can suffice if it suits your style.

Conclusion

In the end, the choice between a rim lock and a mortice latch comes down to your door’s requirements and your priorities:

If you have a period property, thin doors, or simply love the traditional look, a rim lock can be a period-appropriate and practical. It’s easy to fit and adds character but remember its limitations, lower security and specific fitting positions.

If you want a sleek appearance, compatibility with various modern handles, and higher security potential, go with a mortice latch/lock. It’s the standard choice for most doors today. Just ensure you’re prepared for or have help with the installation work.

Often, it’s not an either/or across your whole home – you might use rim locks on some interior doors, for example, a study or a guest room in a period-style home and mortice latches/locks on others, like high-traffic doors or exterior doors where you need more security. Consider the door location (internal vs external), the door’s construction, and the look you’re aiming for.

Frequently Asked Questions

What is a rim lock?

A rim lock is a type of door lock that is mounted on the surface of the door, usually the face that opens towards you. It typically comes as a box that contains a latch and sometimes a deadbolt. Rim locks usually are locked with a key and operated with a knob to retract the latch. They have been around for centuries and are often found in older or traditional-style homes. Unlike a mortice lock, a rim lock is not embedded into the door – it’s fully visible on the door interior. There are locking versions, as well as non-locking versions called rim latches, that just use a latch mechanism for holding the door closed and are operated with a door knob.

What is a mortice latch?

A mortice latch is a door latch mechanism that is fitted inside the material of the door. “Mortice” means a slot cut into the door where the latch sits. A basic mortice locking latch, like a tubular latch, has a spring-loaded bolt that holds the door closed and is operated by a door handle or knob via a spindle. On its own, a latch does not lock with a key – it’s just for keeping the door shut. When people say mortice lock, they usually mean a similar morticed mechanism that does include a key-operated deadbolt. In short, a mortice latch is the internal part that keeps a door closed without a key, mostly used on interior doors with no need for security. It’s hidden inside the door, except for the faceplate and keeper on the door’s edge and door jamb.

Are rim locks secure?

Rim locks provide only basic security. They are generally considered far less secure than mortice locks. A traditional rim lock can be simply unscrewed or forced more easily because it’s screwed to the surface of the door. Many rim locks also have simpler keys that can be picked or bypassed. That said, they are usually acceptable for internal doors where high security isn’t needed. For an external door, a rim lock on its own is usually not sufficient. If you like the convenience and style of a rim lock, it should be supplemented with a robust mortice deadlock for true security. Always check your insurance requirements: most UK insurers require a certified 5-lever mortice deadlock on external.

Can I use a rim lock on an exterior door?

You can physically install a rim lock on an exterior, but it’s not recommended as the sole locking mechanism. Rim locks used externally should ideally be secondary locks. For any important external door you should also have a strong mortice deadlock or equivalent. Rim locks on their own don’t offer enough resistance to forced entry. Additionally, if your door opens outward, away from the inside of the house, a standard rim lock would end up on the outside of the door – which is not secure and usually not workable. So, rim locks are generally suited to inward-opening doors, and on external doors they must be paired with a certified lock for security.

Are rim locks reversible for left and right-hand doors?

Some are, but not all rim locks are reversible. Many rim locks are manufactured in left-handed or right-handed versions. That means you must choose the correct type depending on which side of the door the lock will be mounted and which way your door opens. A left-hand rim lock, for example, is designed to be fitted on a door that has its hinges on the left, as viewed from the side you’re mounting the lock, and that opens toward you. If you tried to put that same lock on the opposite side or a differently handed door, it wouldn’t function properly – the latch bolt and keyhole opening would be upside down. However, some modern rim locks and latches are marketed as reversible.