A door sill and a door threshold refer to the same physical part of a doorway, the horizontal piece at the base of the opening that the door closes against, and the terms are used interchangeably in most everyday and retail contexts. Where the distinction actually matters is when you're shopping for a seal or replacement part: "threshold" is the more common and more specific term in the garage door industry, while "sill" is used more broadly across all door types and is more common in general construction and window terminology. If you're searching for a garage door product, "threshold seal" will get you more accurate, relevant results than "sill."

Where the Terms Come From

Both words describe the same functional part, a raised or level strip spanning the bottom of a doorway that the door seals against when closed, but they come from slightly different traditions of use.

"Sill" is the older and broader term, used across windows and doors generally in construction and architecture. A window sill and a door sill serve the same structural role, the base of the opening.

"Threshold" became the more specific, more commonly used term for the door-level piece specifically, especially as it relates to weatherproofing, accessibility, and the seal or strip installed at that location. In garage door and commercial door contexts specifically, "threshold" is almost always the term used in product names, industry standards, and building codes, including the ADA Standards for Accessible Design, which uses "threshold" exclusively when specifying height and slope requirements.

Does It Matter Which Word You Use?

For everyday conversation, no, the terms are interchangeable and anyone in the door or construction trade will understand either one. For shopping specifically, using "threshold" will get you more relevant results for garage door and commercial door products, since that's the term the industry has standardized on for the seals, ramps, and accessories in this category. Search "sill" for a garage door product and you'll get a mix of relevant results and unrelated window and general construction hardware; search "threshold" and the results are almost entirely doors.

What a Garage Door Threshold Actually Is

In the specific context of a garage door, the threshold is the strip at floor level, spanning the width of the opening, that the bottom of the door closes against or near. Depending on the door and the property, this might be:

The bare concrete floor itself, with no dedicated threshold piece at all, which is common on older or unmodified garages and is exactly the situation a threshold seal is designed to fix.

An existing raised or recessed threshold, built into the original construction, which a seal can be added to or replace depending on its condition.

A threshold seal, an aftermarket strip of PVC, vinyl, aluminum, or rubber fitted specifically to close the gap between the door and the floor, blocking water, pests, drafts, and debris.

Threshold Seal, Not "Sill Seal"

If you're buying a product to close the gap under your garage door, "threshold seal" is the term to search and the term you'll find on almost every manufacturer's product listing, including GaraDry's. "Sill seal" does exist as a term, but it more commonly refers to a thin foam gasket used under a building's wall sill plate during construction, a completely different product for a completely different purpose. Using the wrong term when searching is a common way first-time buyers end up looking at the wrong category of product entirely.

FAQ

Is a door sill the same as a threshold?

Functionally, yes, they refer to the same part of a doorway, the horizontal strip at the base that the door closes against. "Threshold" is the more specific and more commonly used term in garage door and commercial door contexts, including in building codes and ADA standards.

What should I search for when buying a garage door seal?

Search "threshold seal" or "garage door threshold seal," not "sill seal," which refers to a different, unrelated construction product (a foam gasket used under wall sill plates). Using "threshold" will return accurate, relevant results for the product you actually want.

Why does ADA use the word "threshold" and not "sill"?

The ADA Standards for Accessible Design consistently use "threshold" when specifying height and slope requirements for doorways, which is why "threshold" is the standard term across the door and accessibility industry, even though "sill" describes the same physical feature in general construction usage.

Does my garage door already have a threshold, or do I need to add one?

Many garages, particularly older ones, have no dedicated threshold at all, just bare concrete at the base of the door opening. A garage door threshold seal is designed to add that missing barrier, closing the gap between the door and the floor without requiring any structural changes to the garage.