Though often overlooked, the jamb is one of the secret ingredients to a great door. It carries the weight of both the doorframe and the door, and it’s what your door’s hinges are attached to.
You need the right jamb to match up with the right door. If incorrect, your door may fall and break, not open or close, and rip the hinges from your door frame.
There are two primary types of jamb to consider; flat jambs and split jambs. Both have their strengths and weaknesses, and this article will explore everything you need to know before buying them.
We’ll compare both types across various categories and share expert tips to ensure you get the most out of your doors. Whether you’re installing new doors or retrofitting old ones, we’ve got you covered.
Split vs. Flat
what is a flat jamb?
Before comparing the two types, let’s explain their core differences. Flat jambs are perhaps the most common type of jamb and use standard dimensions to suit most, if not all, modern doorframe styles.
As the name suggests, flat jambs are flat pieces of material (usually solid wood). They can be used decoratively for doorless frames by enclosing cased openings and elevating plain-looking edges into something much more.
But flat jambs also have an essential function when doors are attached. They sit flush against the door frame and, together with a unique molding stop, allow the door to open and close securely without putting too much pressure on hinges or door accessories.
What is a split jamb?
Split jambs are a type of rabbeted jamb that look pretty similar to their flat counterparts on the outside. But the critical difference is how they are made. A split jamb uses two pieces of material that slot together with a tongue and groove.
While the flat jamb is a popular choice for standard door sizes, split jams are ideal for niche, customized doors and unusual shapes. And unlike their flat counterparts, split jambs do not require a separate door stop to be placed within the door frame.
Which is Better?
Now that we know how these jambs are physically different, it’s time to see which is best for your DIY job. We’ll compare and contrast both types across various relevant categories to help you make an informed decision.
1. Standardized size? Winner – Flat jamb
The flat jamb is considered the industry standard jamb, suitable for almost all traditionally sized doors, measuring 4 9/16” wide on average.
If you’re a novice at DIY but have bought a generic door and frame, then the flat jamb is an ideal choice. You can buy these premeasured without much consideration. Similarly, if you’re kitting out a new house with several new doors, nine times out of ten, you and your carpenter will work with flat jambs.
On the other hand, split jambs aren’t suitable for all types of door frames or wall sizes. This is because split jams require a much thicker interior wall than a standard opening, so you must measure your walls accurately. If they’re too thin, you won’t be able to install a split jamb – even if you had your heart set on it
2. Custom-sized doors? Winner – Split jamb
While flat jambs can come in various standard sizes, ultimately, split jambs are the winner in terms of customization.
If you have a unique-shaped door, less-than-plumb walls, or if your wall thickness is above average, split jambs will give you much more choices and design options.
Whether you have an unusual door or want to add a unique design to the frame, split jambs offer much more flexibility and creativity because they can be custom-made to your liking.
3. Easy to install? Winner – Split jamb
Although many people might think more parts = more work, split jambs are much easier to install than flat jambs.
Flat jambs require precise measuring and have a more complex installation process. This is because you need to properly align the “stop” to catch the door before it pulls at the hinges. Additionally, you’ll need to install flat jambs during the doorframe installation to ensure everything connects.
On the other hand, split jambs are installed on interior doors at the very end. They are an ideal choice for novice DIYers wanting to retrofit their homes.
Additionally, split jambs already have casing trim applied to them, removing yet another tedious job from the mix. All you need to do is secure them with 2-inch finishing nails. And because they’re installed last, they can easily be removed and replaced without damaging the original door.
4. Durability: Winner – Flat jamb
Because they are made with just one piece, flat jambs are the easy winner regarding sturdiness, durability, and reliability. They are often made of solid wood to support carrying heavier doors. Especially if you’re considering using a solid core door, they are the recommended choice.
That’s not to say split jambs are cheap or faulty. But because they involve two parts, there is a higher margin of error when measuring, cutting, and sizing it.
5. Cost: Winner – Split jamb
Jambs can be expensive, especially if you are kitting out several doors simultaneously. The average price for jamb installation is between $150-$250, with labor and materials included.
While your price depends on the style, size, and type of door you have, it’s often agreed upon that split jambs are often much cheaper than their flat counterparts. Flats are made with higher-quality materials to carry heavier weights and often have higher-quality finishes that blend with popular doorframe styles.
How do I measure the door jamb?
To calculate the measurement needed for the sides of the jamb, you must first measure the width of your surrounding walls. This will tell you what sized jamb should be installed to allow the door to open and close fully. Add about 1/8 inch to your measurements to give your jamb enough wiggle room to work.
How do I remove my old door jamb?
If you’re renovating your home and want to remove existing door jambs, you must first remove the door. Then, using a utility knife, cut around the trimming to separate it from the wall. Using a screwdriver or pry bar, gently pull away the casing off the jamb.
If your jamb is secured in place with finishing nails, use a screwdriver to unscrew the jamb, and like the trim, use a pry bar to pull it from your doorframe gently.
Below are some tips to keep in mind, irrespective of the type of jamb you install:
- Before installing wooden door frames and jambs, allow enough time for the material to adapt to the room’s temperature for a few days.
- When working out the jamb width, remember to include the wall stud and the plaster, drywall, or sheetrock thickness in your measurements.
- Are you a novice DIYer? Then you might consider buying pre-hung doors from a manufacturer, which promises a straightforward, stress-free installation.
- If your measurements are incorrect and your door does not perfectly align, don’t panic. Weatherproof seals can help bridge any minor gaps between the jamb.
- Split jambs are often much cheaper, especially when bought in bulk. They can be cost-effective if planning to renovate or remodel several doors simultaneously.
- Remember to factor in the weight of your door! Solid core doors are hefty and will demand more support from their jamb than standard doors.
- Door jambs should last decades before needing replacements. The only main danger to them is rot and physical damage.
Whether building a new home or simply renovating an older room or two, interior door jambs are among the most important things to consider.
The right jamb ensures that your door will stay in position for a long time and can open and close without causing damage to the doorframe, walls, hinges, or flooring.
As our article has shown, both flat and split jambs offer a wide range of possibilities. But there comes a time and place when one excels over the other.
Flat jambs are popular and often are the go-to choice when installing standard-sized doors, while split jambs are cheaper, more flexible, and easier to install.
Ultimately, when making your choice, you will need to consider the style and weight of the door you are hanging and the thickness of the wall surrounding the doorframe.
Please comment below if you have any questions about what kind of jamb you should use for your door installation or have tips to share.
As a quick reminder, remember:
- A door jamb supports the weight of both the door and the doorframe.
- Flat jambs are the most common and often used for traditionally sized doors.
- Split jambs are cheaper, more flexible, and useful for customized doors or when your walls are thicker than average.