Quick answer
An exterior door threshold is the strip fixed across the bottom of an outside door opening, between the jambs, that the door closes against to block air and water while giving a durable surface to step over.
It works with the door sweep, the sill pan or flashing below it and the landing outside. Its height also sets how far the floor and landing may sit below it under the residential code.
Quick facts
The key facts about Exterior Door Threshold, with sources:
- Main jobs
- Seal the gap under the door; shed water; carry foot traffic 4
- IRC landing drop, required egress door
- Landing no more than 1-1/2 in below the top of the threshold 1
- IRC exterior exception
- Up to 7-3/4 in below if the door does not swing over the landing 1
- ADA maximum (public buildings)
- 1/2 in; existing or altered up to 3/4 in with beveled sides 2
- Rated as part of
- The whole door unit, by NFRC (U-factor, air leakage) 45
- Egress door clear height
- At least 78 in from top of threshold to bottom of stop 1
Key takeaways
- The threshold is the sill strip the door seals against; it stops drafts and water at the bottom of the opening.
- In the 2021 IRC, the floor or landing at the required exit door may sit no more than 1-1/2 inches below the top of the threshold, with a 7-3/4 inch exception outside.
- Public buildings under the ADA cap thresholds at 1/2 inch, which is a useful target for low-step home entries.
- Most leaks at doors start below the threshold, so a sill pan or flashing under it matters as much as the threshold itself.
- Adjustable thresholds and new sweeps fix many drafts without replacing the door.
What a threshold is, and what it is not
Look down at the bottom of your front door. The metal or wood strip you step over is the threshold. On most modern prehung doors it is aluminum with a vinyl or rubber insert on top. The bottom of the door carries a sweep that presses against that insert when the door closes.
People use “sill” and “threshold” loosely. In practice, the sill is often the sloped bottom member of the door frame that sheds water out, and the threshold is the part on top that the door seals against.
On many factory door units they are one extruded piece. Either way, the job is the same: close the gap, shed water, and survive foot traffic.
The threshold is part of the door unit’s energy rating. ENERGY STAR bases its door criteria on glazing level and on ratings certified by the National Fenestration Rating Council (NFRC) 4, and the NFRC label includes air leakage, which measures how much air comes through the product 5.
A worn threshold insert can undo that rating in the field. For complete door units, see our prehung door unit page.
How a threshold keeps water and air out
A threshold works as one layer in a small system at the bottom of the door.
- Slope out: the sill slopes toward the outside so water runs away from the house.
- Seal up: the door sweep presses against the threshold insert to block air.
- Catch below: a sill pan or flashing under the threshold catches any water that gets past and drains it out.
- Seal the ends: corner pads or seals close the gap where the threshold meets the jambs and weatherstrip.
- Support: the subfloor or shims under the threshold keep it from flexing and opening a gap.
- Door sweepRubber or vinyl fins on the door bottom
- Threshold insertSoft cap the sweep seals against; often adjustable
- Threshold or sillAluminum, wood or composite, sloped to drain out
- Sill pan or flashingCatches water and drains it to the outside
- Subfloor and rimSolid, level support under the sill
A typical modern assembly. Exact parts vary by door maker; follow their installation instructions.
Types of exterior door thresholds
| Type | What it is | Best fit |
|---|---|---|
| Adjustable threshold | Insert raised or lowered with screws | Entry doors where the gap changes with seasons or settling |
| Fixed bumper threshold | Vinyl bumper fixed in a metal saddle | Simple replacements and garage-to-house doors |
| Wood sill and threshold | Hardwood sill, often oak | Older homes and custom doors; needs finish upkeep |
| Composite sill | Rot-resistant composite core | Wet exposures where wood sills have failed |
| Low-profile or ADA-style threshold | Short, beveled threshold | Step-free entries; 1/2 inch is the ADA limit for public buildings 2 |
| Sliding patio door sill | Track sill with drainage weeps | Patio and deck doors; keep weeps clear |
Example: checking a back-door landing against the 2021 IRC
A homeowner replaces the door from the kitchen to a deck. The door is the home’s required egress door, and it swings in. Here is how three landing heights compare with 2021 IRC R311.3.1 1.
| Situation | Model-code rule | Result |
|---|---|---|
| Inside floor 1/2 in below top of threshold | Not more than 1-1/2 in lower | Meets the rule |
| Deck landing 4 in below top of threshold; door does not swing over it | Exterior side may be up to 7-3/4 in below | Meets the exception |
| Deck landing 9 in below top of threshold | More than 7-3/4 in | Fails; raise the landing or add a step built as a code stair |
| Landing 30 in deep in direction of travel | At least 36 in deep 1 | Too short; enlarge it |
The same section requires a landing on each side of each exterior door, at least as wide as the door and at least 36 inches in the direction of travel, with an outside slope no steeper than 1/4 inch per foot 1.
Doors other than the required exit door may have landings up to 7-3/4 inches below the threshold 1. Your jurisdiction’s adopted code governs.
Where the threshold shows up in a remodel
On the door order. Prehung units list the sill type and height. For a step-free entry, specify a low-profile sill early; changing it later may mean recessing the subfloor.
On the floor plan. New flooring changes the inside floor height. A thick tile job can leave the threshold too low and the sweep dragging. Check heights when you plan flooring with our flooring calculator.
On the deck or porch plan. The landing outside is tied to the threshold height by code 1.
In the bid. Look for a sill pan or flashing line item. “Install door” alone may not include it.
Do the dollar-bill test, without the dollar
Close the door on a strip of paper at several points along the threshold. If it slides out with no drag, the sweep is not sealing there. Raise an adjustable insert or replace the sweep, and test again.
Benefits and limits of a well-set threshold
Benefits
- Stops drafts at the bottom of the door, one of the most noticeable leaks.
- Sheds rain and snowmelt away from the floor and subfloor.
- Low-profile versions make step-free entries possible.
- Adjustable inserts let you tune the seal without new hardware.
Limits
- A threshold cannot stop water that gets under it; that is the sill pan’s job.
- Low thresholds need more careful drainage and overhang protection.
- Inserts and sweeps wear out with traffic.
- Raising the inside floor can push the threshold out of the code height range 1.
What a threshold cannot fix
A new threshold does not fix a door that is out of square, a frame that has racked, or a rotten subfloor under the sill. If the door rubs at the top corner or the gap at the bottom tapers, the problem is in the frame or the house, not the threshold.
A threshold also does not replace flashing. Water that runs down the wall or blows in at the corners can travel under the sill and into the floor framing. That is where a sill pan and proper wall flashing matter. See our window flashing page for the same principles at windows.
What drives the cost of threshold work
We do not quote prices. The drivers are whether you replace only the insert or sweep, the threshold alone, or the full door unit; the sill material; whether the subfloor below is sound; whether a sill pan must be added; and whether the landing outside must change to meet code.
Life span depends on traffic and weather. Vinyl inserts and sweeps are wear parts. Aluminum thresholds last longer but can loosen. Wood sills last as long as their finish is kept up. Door warranties from makers often depend on installation per their instructions. For whole-project budgets, see our cost guide.
How a threshold is replaced or installed
Swapping an insert or sweep is a simple owner task. Full threshold or door replacement is usually a carpenter’s job.
- Measure the opening between jambs and the height of the existing sill.
- Check the subfloor under the sill for rot or soft spots.
- Install or confirm a sill pan or flashing that drains to the outside.
- Set the threshold in sealant per the maker’s instructions, level and supported along its length.
- Seal the ends at the jambs and adjust the insert to the sweep.
- Check the inside floor and outside landing heights against your local code 1.
Threshold upkeep
- Clean grit out of the insert and the sliding-door track; grit wears seals.
- Re-adjust an adjustable insert when the seasons change the gap.
- Replace cracked inserts and flattened sweeps.
- Keep wood sills finished; bare wood absorbs water and checks.
- Keep patio-door weep holes open so water can drain out.
Warning signs and when to call a pro
- Soft or stained flooring inside the door. Water is getting under the sill.
- Light under the closed door. The sweep or insert is not sealing.
- A threshold that flexes underfoot. Missing support or a rotted subfloor.
- A trip edge after new flooring or a new deck changed the heights 1.
- Musty smell near the door. Hidden moisture; check for mold.
Rot under the sill can reach the framing
If the floor near the door is soft, the rim joist or floor framing below may be damaged.
Do not cut into structural framing yourself; have a contractor open the area, and bring in an engineer if structural members are rotted.
In homes built before 1978, cutting or sanding old painted trim must follow EPA lead-safe practices.
Code and standards for thresholds
2021 IRC R311.2 and R311.3. Each home needs at least one side-hinged egress door with a 32 inch clear width and a 78 inch clear height measured from the top of the threshold.
R311.3 requires a landing on each side of each exterior door; R311.3.1 limits the floor or landing at the required egress door to 1-1/2 inches below the top of the threshold, with a 7-3/4 inch exterior exception when the door does not swing over the landing; R311.3.2 limits other exterior doors to 7-3/4 inches 1.
2010 ADA Standards 404.2.5 and 303. In public buildings, thresholds are capped at 1/2 inch. Changes in level up to 1/4 inch may be vertical; from 1/4 to 1/2 inch they must be beveled no steeper than 1:2 2.
The Access Board notes these rules apply to doors that must comply, including sliding doors 3. They do not bind private houses but are a sound target for step-free entries.
Ratings. ENERGY STAR door criteria rest on NFRC-certified ratings by glazing level 4; the NFRC label reports air leakage and U-factor 5.
Local adoption. States and cities adopt and amend the IRC. Check what your building department enforces.
Threshold vs related door parts
| Part | What it does | Main difference |
|---|---|---|
| Threshold | Surface the door seals against at the bottom | Fixed to the opening |
| Door sweep | Seal strip on the door bottom | Moves with the door |
| Sill pan | Tray under the sill that drains water out | Hidden; the backup for leaks |
| Weatherstripping | Seals at the jambs and head | Sides and top, not the bottom |
| Weather-resistant barrier | Wall layer that sheds water behind siding | Ties into flashing around the door |
Threshold myths
- Myth Caulk along the threshold stops leaks.
- Reality Caulk on top can trap water; a sill pan and correct flashing below are what stop leaks.
- Myth The ADA half-inch rule applies to my house.
- Reality ADA Standards cover public places; homes follow the residential code 3 1.
- Myth Any landing height is fine outside.
- Reality The IRC limits how far the landing may sit below the threshold 1.
- Myth A drafty door needs replacing.
- Reality Often an insert adjustment or new sweep fixes it.
- Myth The NFRC rating covers my installation.
- Reality Ratings are for the product as tested; field installation decides real-world sealing 5.
Climate and exposure change the details
Doors facing driving rain with little overhang need the most careful sill pans and the most water-tolerant sill materials. In snowy climates, snow piled against a low threshold can melt inward. In hot, sunny exposures, vinyl inserts age faster.
The height rules come from your adopted code edition, which your building department can confirm. We do not give a state-by-state list because the variable is exposure at the door, not the state line.
When the threshold should change your plan
If you are aging in place or planning a step-free entry, decide on a low-profile threshold before you order the door, and plan the floor and landing heights around it. Our accessibility remodeling page covers the wider picture.
If the floor by a door is soft or stained, solve the water path before buying a new door. Our kitchen remodeling page covers how back-door and deck connections often get folded into a kitchen job.
- If Draft at the bottom, door otherwise fine
- Then Adjust the insert or replace the sweep
- If Water stains or soft floor inside
- Then Open up, repair, add a sill pan
- If New flooring raises the inside floor
- Then Re-check threshold height and door swing
- If Step-free entry wanted
- Then Specify a low-profile threshold and plan drainage
Questions about Exterior Door Threshold
What is an exterior door threshold?
It is the strip across the bottom of an outside door opening that the door closes against. It blocks drafts and water and gives a durable surface to walk over. On most new doors it is aluminum or composite with a soft insert that the door sweep seals against.
What is the difference between a door sill and a threshold?
The sill is usually the sloped bottom member of the frame that sheds water out; the threshold is the part on top that the door seals against. On many prehung doors they are one piece. People often use the words interchangeably.
How high can an exterior door threshold be?
The 2021 IRC limits how far the floor or landing can sit below the threshold rather than setting the threshold height itself. At the required exit door, the floor or landing may be no more than 1-1/2 inches lower, or up to 7-3/4 inches outside if the door does not swing over the landing.
What is an ADA-compliant threshold?
In public buildings under the 2010 ADA Standards, thresholds may be no more than 1/2 inch high, with changes over 1/4 inch beveled. Existing or altered thresholds may be up to 3/4 inch with beveled sides. Private homes are not bound by the ADA, but the half-inch target helps wheelchair and walker users.
How do I stop a draft under my front door?
First check the seal: close the door on a strip of paper along the threshold. If it slides out easily, raise an adjustable insert or replace the door sweep. If the gap tapers or the door rubs elsewhere, the frame may be out of square and need a carpenter.
Why is water coming in under my door threshold?
Often because there is no sill pan or flashing below the threshold, or it was installed wrong, so water that gets past the sill drains inward. Clogged weeps on patio doors and a landing that slopes toward the house also cause it. Fix the water path before replacing the door.
Can I replace just the threshold?
Often, yes. Inserts and sweeps are simple swaps, and many thresholds can be replaced without removing the door. If the sill is part of a factory door unit or the subfloor under it is rotted, a carpenter may need to replace the unit or repair the framing first.
Does a new floor affect my door threshold?
Yes. Raising the inside floor with thicker flooring can leave the threshold too low, make the door drag, or change the height relationship the code sets at the exit door. Check heights and door clearance before choosing flooring thickness.
Do door thresholds affect energy ratings?
They are part of the door unit that NFRC rates, including air leakage. ENERGY STAR door criteria rely on those NFRC ratings. A worn or misadjusted threshold insert can let in more air than the label suggests, so keep it adjusted.
Sources
- ICC, 2021 International Residential Code, Chapter 3 Building Planning (R311.2 egress door, R311.3 landings at exterior doors), retrieved .
- U.S. Department of Justice, 2010 ADA Standards for Accessible Design (303 changes in level, 404.2.5 thresholds), retrieved .
- U.S. Access Board, ADA Standards Chapter 4: Accessible Routes, retrieved .
- ENERGY STAR, Residential Windows, Doors and Skylights: Key Product Criteria, retrieved .
- National Fenestration Rating Council, Consumers (label ratings), retrieved .
Expert review
Written by the HyreRemodel Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Egress door size, landings and threshold-to-landing limits were read from 2021 IRC R311.2 and R311.3 on ICC Digital Codes.
Threshold and change-in-level limits from the DOJ 2010 ADA Standards PDF and the Access Board chapter 4 page; door rating basis from ENERGY STAR’s key product criteria page; label terms from NFRC’s consumer page.
The landing example applies model-code numbers to sample heights. Assembly layers describe typical practice, not a code requirement. No prices are given.
Suggest a correction. We fix errors and say what changed.