What a threshold is and why it fails

A threshold is the horizontal piece that sits at the bottom of a doorway, between the inside and outside. It seals the gap between the floor and the door frame, keeps water and drafts out, and gives your foot something to step over. Most thresholds are made of wood, aluminum, or composite material, and they wear out because they take constant foot traffic, weather exposure, and the weight of the door itself.

A threshold fails when it cracks, rots, warps, or no longer sits flush against the floor. Water pools on top instead of draining away. The door drags or won't close properly. You feel drafts or see daylight underneath. Replacing it is a straightforward job that takes two to four hours and costs between $50 and $300 in materials, depending on the door type and threshold quality.

Key Takeaways

  • Remove the old threshold by prying it up with a flat bar, then scrape away old caulk and adhesive so the floor is flat and clean.
  • Measure the width of the doorway opening and the height of the existing threshold to buy the correct replacement size.
  • Set the new threshold in place, shim it level, and find it with screws or nails driven through the pre-drilled holes into the subfloor.
  • Seal the edges with caulk rated for exterior use so water cannot run underneath and rot the subfloor.
  • If the subfloor is soft, spongy, or visibly rotted, call a carpenter before installing the new threshold, because the damage goes deeper than the threshold itself.

Gather your tools and materials

You will need a flat pry bar or old chisel, a hammer, a tape measure, a level, a drill with bits, a caulking gun, and a handsaw or circular saw if the threshold needs to be cut to width. Have a shop vacuum or broom ready because removing the old threshold creates dust and debris.

For materials, buy a replacement threshold that matches your door type — interior thresholds are thinner and made of wood or composite, while exterior thresholds are taller and often aluminum or composite with a rubber seal. Bring the old threshold to the store if you can, or measure the width of the doorway opening and the height of the existing threshold. You will also need exterior-grade caulk (silicone or polyurethane), wood screws or galvanized nails sized to the threshold manufacturer's instructions, and shims if the subfloor is uneven.

Remove the old threshold

Close the door and look at how the old threshold is fastened. Most are screwed or nailed down through the top surface into the subfloor. Use a flat pry bar to lift one end gently — do not force it or you will crack the surrounding flooring. Work your way along the length, lifting a little at a time until the threshold comes free.

Once it is out, scrape away all old caulk, adhesive, and debris from the floor with a putty knife or old chisel. The surface must be clean and flat so the new threshold sits tight. If you see soft or spongy wood, poke it with a screwdriver — if it sinks in easily, the subfloor has water damage and needs repair before you install the new threshold. Stop here and call a carpenter.

Measure and cut the new threshold to fit

Measure the width of the doorway opening from the inside edge of one side jamb to the inside edge of the other. This is the length your threshold needs to be. Most thresholds come slightly oversized so you can trim them to fit.

If the threshold is longer than your opening, mark the cut line on both sides and use a handsaw or circular saw to cut it square. Test-fit it in the doorway — it should slide in snugly without forcing. If it is too tight, sand or plane the ends slightly. The goal is a fit that is snug but does not require hammering.

Set the threshold level and find it

Place the threshold in the doorway opening. Use a level to check that it sits flat from side to side and front to back. If the floor is uneven, use shims under the threshold to bring it level — slip them under the low spots and tap them gently until the level reads true.

Once it is level, drill pilot holes through the pre-drilled holes in the threshold into the subfloor. Use screws or nails sized to the manufacturer's instructions — typically 2.5-inch galvanized screws for exterior doors or 1.5-inch screws for interior thresholds. Drive them in firmly so the threshold is pulled down tight, but do not over-tighten or you will crack composite material. Space fasteners about 12 inches apart along the length.

Caulk the edges to seal out water

Once the threshold is fastened, run a bead of exterior-grade caulk along both long edges where the threshold meets the floor and the side jambs. This prevents water from running underneath and rotting the subfloor. Use a caulking gun and smooth the bead with a wet finger or caulk tool so it sits flush.

Let the caulk cure for the time specified on the tube — usually 24 hours — before closing the door fully or allowing foot traffic. If the threshold has a rubber seal on the underside, do not caulk over it; the seal is designed to compress slightly as the door closes.

When to call a professional

If the subfloor is soft, spongy, or visibly rotted, the damage extends beyond the threshold itself and needs a carpenter to assess and repair. If the doorway is not square — the side jambs are not plumb or the opening is wider at the top than the bottom — a threshold will not sit flush and the door will not close properly. A carpenter can shim the jambs or adjust the opening before installing the threshold.

If the door frame itself is damaged, warped, or the hinges are failing, replacing the threshold alone will not solve the problem. Have the frame inspected before you buy materials.

Frequently Asked Questions

Can I replace a threshold without removing the door?

Yes. Close the door and work underneath it. You may need to remove the door if the threshold is wedged tightly under the frame or if you need to access fasteners on the inside edge, but most replacements can be done with the door in place. If the door is in the way, remove the hinge pins by tapping a nail up through the bottom of the hinge and lifting the door off.

What if the new threshold is slightly shorter than the old one?

Measure the width of the doorway opening, not the old threshold. Thresholds come in standard widths — 36 inches for standard doors, 32 inches for narrower openings. If your opening is between sizes, buy the larger one and trim it down. If it is shorter than the opening, you cannot use it; return it and order the correct size.

Do I need to remove the door sweep or weatherstripping?

Check the bottom of the door. If there is a rubber sweep or weatherstripping, it may need to be adjusted or replaced after the new threshold is installed because the height has changed. Test the door closure after installation — if it drags or does not seal, the sweep may need to be lowered or replaced.

What is the difference between interior and exterior thresholds?

Exterior thresholds are taller, have a slope to shed water, and often include a rubber seal. Interior thresholds are thinner and made of wood or composite. Use the correct type for your door location — an interior threshold on an exterior door will not shed water and will rot quickly.

How long does a new threshold last?

A well-installed threshold with proper caulking lasts 10 to 20 years. Exterior thresholds wear faster than interior ones because of weather exposure. Inspect the caulk every few years and re-caulk if it cracks or pulls away from the edges.