Door Sill vs. Threshold: What’s the Difference?

How can you tell a door sill from a threshold?

A door threshold in front of welcome doormat
Photo: Image Source / Connect Images / Getty Images
A door threshold in front of welcome doormat
Photo: Image Source / Connect Images / Getty Images
Highlights
  • Door sills and thresholds are located close to one another at the bottom of an exterior doorframe, but they’re not the same part. 

  • Door sills are a structural element, and thresholds direct the flow of water to prevent leaks.

  • Sills are made of wood, while thresholds are made of aluminum.

Get quotes from up to 3 pros!
Enter a zip below and get matched to top-rated pros near you.
Geo Icon

It’s easy to confuse these two terms because a door sill and a threshold are installed in the same location at the bottom of a door. The differences between these two parts of a door lie in their function and the order in which they’re installed. The sill acts as a structural element, while the threshold protects the sill and the home's interior from water. Read on for what you need to know to differentiate between a door sill and a threshold. 

What Are the Differences Between a Door Sill and a Threshold?

The threshold of an exterior door
Photo: akurtz / E+ / Getty Images

Door sills and thresholds are located in nearly the same spot, so it can be tricky to tell the difference. The doorframe rests on the door sill, and the threshold sits on the sill and between the door jambs. It helps to think of these parts in layers.

The sill is the first layer that rests on the foundation, deck, or porch. Once the doorframe is installed, the threshold is tucked between the two door jambs and sloped to direct water away from the door to prevent leaks from getting through.

DifferenceSillThreshold
LocationBottom of the doorOn top of the sill
MaterialsMetal, wood, concreteMetal, fiberglass, wood
FunctionBase of the doorframeTransition piece that prevents water from entering

If you need a new door sill or threshold, a door installer can help get your door working like new.

Location Differences

While the sill and the threshold are installed at the bottom of the door, their location is substantially different. The sill is located at the bottom of the doorframe between the studs and acts as a base for the door and the frame. The threshold sits on top of the sill and helps stop water from leaking into the structure's interior.

Material Differences

As the base of the doorframe, the sill can be made from wood, metal, or concrete. The threshold of an exterior door is made of metal, such as aluminum, brass, or stainless steel, but it can also be made from fiberglass or include vinyl or wood elements. 

Functional Differences

The sill and the threshold work together to keep moisture out of the house, but they do so in different ways. The threshold is the first line of defense against the elements, and its slanted design allows water to drain away from the door. Because it’s made of a durable material like metal or fiberglass, it’s also effective at protecting the sill from damage. If the threshold itself becomes damaged, it can be replaced relatively quickly.

The sill supports the frame and door casing and creates a layer of protection between the foundation and the door. To add more protection from water, you can also install a sill pan between the sill and the threshold. 

Installation Differences

A person installing a door threshold
Photo: retbool / Adobe Stock

The installation process for sills and thresholds have some similarities, but there are different challenges to tackle with each. The sill is installed with the original door, which gives plenty of room to work. 

If you need to replace a rotted or damaged sill, you’ll have to remove the threshold. You’ll have to cut the sill out while keeping the doorframe and casing intact. Then, you’ll cut a new sill to size, notching the corners to fit under the door, and make sure it sits firmly against the studs on either side of the frame. 

If you’re installing a pre-hung door, it might come with an installed threshold, so all you have to do is set it in the opening and secure it with screws or nails. If you’re installing a new threshold on an existing door, you’ll have to remove the old one and cut the new one to size, notching the corners so it sits snugly against the stops inside the doorframe. A local door repair company can install these elements so your door functions properly.

Frequently Asked Questions

Sometimes, these two terms are used interchangeably, but they are separate parts of a door, and each serves a different function. The sill helps ensure the doorframe is secure, and the threshold helps protect the sill and direct water away from the door to prevent leaks.

Yes, you need to install a sill for an exterior door. A sill offers structural support for the doorframe and creates a place to install the threshold, which is essential for keeping water from seeping underneath the door and into the home. Door sills are not necessary for interior doors.

Need professional help with your project?
Get quotes from top-rated pros.
The homeowners guide to door services
From average costs to expert advice, get all the answers you need to get your job done.
Woman using her phone standing in front of a french door
May 16, 2025
May 16, 2025
French doors upgrade your space and fill it with natural light. Use this guide so that you can accurately budget the cost to install French doors.
A pocket door in a spacious interior
May 20, 2025
May 20, 2025
The average cost to install a pocket door is $1,050, but prices can range from $800 to $2,500, depending on the type of door, materials, and scope.
Screen door mesh close-up
May 7, 2025
May 7, 2025
Create more usable space by installing a garage door screen, which allows for entertaining or working with plenty of fresh air and zero bugs. Here’s how much installing a garage door screen will cost you.
Little kid reaching for door handle
May 5, 2025
May 5, 2025
Door knobs and door levers are standard opening mechanisms used in modern homes. Learn their differences and how to find the right one for you.
A happy baby in front of an open door
May 12, 2025
May 12, 2025
Before diving into home renovations, get to know both sides of the solid core vs. hollow core door dispute and why there's a time and a place for each one.
Young boy closing fiberglass entry door
May 27, 2025
May 27, 2025
If you need help choosing a new entry door, this list of pros and cons of fiberglass doors will let you see if one of the most popular door options is right for you.