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The Open & Shut Anatomy of a Door: Important Parts of a Door & Door Frame

Although a door may seem simple, there's much more than what meets the eye. To provide the necessary insight on the parts of a door, the team at Frank Lowe has created an open & shut guide to the anatomy of a door. Continue reading to learn more about the anatomy of a door. 

The Jamb Components

The door frame is often called a jamb. In either case, it's made up of three separate pieces that work to surround the door to form a frame, which houses and supports the door. 

  • The head jamb is the top of the frame, and it runs horizontally. Also called the "door header," this part can have simple molding or look very straightforward. It features a stop at the lower edge in addition to weatherstripping to create a proper seal and ensure the door closes firmly. 
  • The two vertical frames on the sides known as side jambs. You may also hear them referred to as:
  • The strike jamb for the side that houses the strike plate and functions with the locking mechanism, and
  • The hinge jamb for the side with the door hinges.

Frames can be manufactured from solid wood, composite material, or veneered wood. The best frames are composite door frames because they are ideal for all types of exposures, do not rot, or absorb moisture. 


A mullion is a critical component for when two individual doors are joined. The mullion is the  seam located between the door frames. 


Also called rebates, margins are the spaces between the door frame and the door. Margins are critical when examining issues with the hinge jamb. And these spaces can be segmented into different types, including:

  • Hinge margin
  • Header or top margin
  • Bottom or sweep margin
  • Strike margin

The Threshold

The threshold is located at the bottom of the door frame and is the area that must be crossed to pass through the door. The threshold contains the door sill. The bottom rail is the bottom section of the door panel that crosses the threshold. 

In the event a door has weather sealing problems, the sill, bottom rail, and/or threshold could be the culprit. Maintaining a proper seal between the threshold and door can lead to greater energy efficiency gains. 

The Door Sill 

The door sill is connected to the frame on both sides and is angled away and down from the bottom of the door. This design helps prevent moisture from accumulating and making its way into the home. Sills are available as adjustable models and fixed models. 

Sills that are adjustable include a cap that can be maneuvered down and up to ensure a tight seal with the door sweep. Sills are offered in aluminum with hardwood bottoms or composite bottoms or in types of wood, such as oak and mahogany. 

As we previously mentioned, sills made from composite materials will not rot and are impervious to moisture. Most commercial buildings employ public access sills that use wheels to roll over its easy-access low profile with simplicity. 


The glazing of the doors is the glass. Modern glazing on exterior doors is comprised of two or three layers of glass. An inert gas, such as argon, will be injected between the layers of glass to provide extra insulation. 

Almost invisible coatings are added to the glass to limit the amount of heat and light reflected away from it or conducted through it. Glazing can be bolstered by laminations and tints to improve privacy, increase strength, and provide decorative elements. 

Weather Proofing 

Every door will employ a door sweep and weatherstrip to protect the structure from the elements and keep conditioned air inside. 

The Weatherstrip

The weatherstrip is a flexible, foam-filled strip that is attached on the outside of the frame where the door sits. When the door is closed, it compresses the weatherstrip to create a tight seal that prevents moisture and air from entering the structure. 

The Door Sweep

The door sweep is located on the bottom of the door and connected to the underside of the door slab to create a seal between the sill and the door sweep. As an additional barrier, the sweep also works to prevent moisture and air penetration. 

Hinge Parts of the Door 

Door hinges attach to the door frame and allow the door to close and open. Hinges also assist in the proper positioning of the door for a tight seal. These components can have a square corner or a curved corner and may be manufactured as non-ball bearing or as ball bearing. However, hinges that are ball bearing will typically last longer and offer smoother operation. Hinges are available in a vast myriad of finishes to complement the style of the door. 

Contact the Fenestration Experts at Frank Lowe

For over 65 years, Frank Lowe has been an industry leader in the fenestration as well as glass & glazing markets. We are a flexible, customer-focused custom manufacturer who offers decades of experience providing key solutions and components for outdoor and indoor windows, door manufacturers, skylights, and virtually any other opening designed to emit light or provide passage from one space to another. At Frank Lowe, we pride ourselves in being the one-stop shop for custom door and fenestration components. 

Contact Frank Lowe today for your custom fenestration and door manufacturing needs.

About the Author Randy Cohen

Since 2002, Randy Cohen has served as the Senior Vice President of Frank Lowe — leading Sales and Marketing as well as a variety of Administrative operations. Randy has 25 years of experience with a background in sales & marketing, production and business management, serving both government agencies and private industry. He holds a B.A from Syracuse University and a Masters and Professional Diploma from Fordham University. Randy uses his unique set of experiences to help businesses and entities across all sectors explore, pursue, and create better solutions.

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