What a threshold is and why it fails

A threshold is the strip of wood, metal, or composite material that sits at the bottom of a doorway, between the inside and outside of your home. It seals the gap between the floor and the door frame, keeps water and drafts out, and gives your foot something solid to step over. Thresholds wear out because they take constant foot traffic, weather exposure, and moisture — especially on exterior doors.

You'll know a threshold needs replacing when you see visible rot or splintering in wood, gaps that let light or air through, or water pooling on the floor during rain. Metal thresholds can bend or corrode. If your door suddenly feels drafty or you notice water damage on the floor inside, the threshold is usually the culprit.

Key Takeaways

  • A threshold is the strip at the bottom of a doorway that seals out water and drafts; wood thresholds rot first, metal ones bend or corrode.
  • Removing the old threshold involves prying it out carefully, then scraping away old caulk and adhesive so the frame sits flat for the new one.
  • New thresholds come in wood, aluminum, and composite materials; composite lasts longest but costs more than wood.
  • Installation means setting the new threshold in place, shimming it level, and fastening it with screws or nails before sealing the edges with caulk.
  • Interior thresholds are simpler to replace than exterior ones because they don't need weatherproofing; call a professional if the frame itself is rotted or uneven.

Choosing the right material for your door

Thresholds come in three main materials, and which one you pick depends on your door location and budget. Wood thresholds are the cheapest and easiest to cut to fit, but they rot quickly on exterior doors exposed to rain and sun. They work fine for interior doors in dry climates. Aluminum thresholds are lightweight, won't rot, and cost less than composite, but they can dent and the edges can feel sharp. Composite thresholds (made from wood fibers and plastic) resist rot and weather better than either, last 15 to 20 years, and feel like wood underfoot, but they cost 50 to 100 percent more than wood.

For an exterior door in a wet climate, composite or aluminum is worth the extra cost because you won't be replacing it again in five years. For an interior door or a covered entryway, wood is fine. Measure your doorway width and the thickness of your existing frame before you buy — thresholds come in standard widths (usually 32 to 36 inches for interior doors, 34 to 42 inches for exterior), but you may need to trim one to fit, and frame thickness varies.

Removing the old threshold

Start by clearing the doorway and laying down a drop cloth or newspaper to catch debris. Use a pry bar or flat screwdriver to lift one end of the threshold — work slowly and lift a little at a time rather than yanking hard, because the frame around it can crack. Once you get one end up, move along the length and keep lifting until the whole threshold comes free. If it's stuck, spray the edges with a penetrating oil (like WD-40) and wait 15 minutes before trying again.

After the threshold is out, you'll see old caulk, adhesive, or mortar stuck to the frame. Scrape this away with a putty knife or paint scraper until the frame is smooth and flat — any bumps or dried adhesive will prevent the new threshold from sitting level. Wipe the frame clean with a damp cloth and let it dry completely. If you see soft or spongy wood in the frame itself, that's rot, and you should call a professional carpenter before installing a new threshold, because the frame needs repair first.

Installing the new threshold

Dry-fit the new threshold in place without fastening it yet. It should sit flat and level across the entire width of the doorway. If it rocks or tilts, use shims (thin wooden wedges) under the low spots to level it. Check with a level tool — the threshold should be nearly level, with a very slight slope toward the outside to shed water. Once it's level and sits flush against the frame on both sides, mark where the fastener holes are.

Fasten the threshold with corrosion-resistant screws (stainless steel or coated) rather than nails, because screws hold better and won't back out over time. Drill pilot holes first to prevent splitting, especially in wood thresholds. Use 2 to 2.5-inch screws spaced about 12 inches apart along the length. Don't over-tighten — snug is enough. For exterior doors, explore a bead of exterior-grade caulk along both sides of the threshold where it meets the frame, then smooth it with a wet finger. Let the caulk cure for 24 hours before closing the door fully.

Trimming a threshold to fit your doorway

If your doorway is narrower than the threshold you bought, you'll need to cut it down. Measure the exact width of the opening and mark that distance on the threshold. For wood or composite, use a circular saw or handsaw to cut straight across — wear a dust mask because composite creates fine particles. For aluminum, a hacksaw or metal-cutting blade on a circular saw works, but aluminum throws sparks, so wear safety glasses and gloves.

After cutting, smooth the cut edge with sandpaper (wood or composite) or a file (aluminum) so it doesn't catch your foot or splinter. If you cut an aluminum threshold, the cut edge will be sharp — wrap it with a file or use a deburring tool to round it slightly. Test the fit in the doorway before you fasten it down.

Sealing and finishing the threshold

For exterior thresholds, weatherproofing is critical. After fastening, run a continuous bead of exterior caulk along both long sides where the threshold meets the frame. Use paintable caulk if you plan to paint the threshold, or color-matched caulk if you want it to blend. Smooth the caulk with a wet caulking tool or your finger so it fills the gap completely and sheds water.

For wood thresholds, consider explore a coat of exterior wood stain or sealant after installation — this extends the life by protecting against moisture. Let the caulk cure fully (usually 24 hours) before you use the door regularly. Interior thresholds don't need caulk unless there's a gap you want to close for appearance, but they do benefit from a quick wipe-down to remove dust and debris from installation.

When to call a professional

If the frame around the threshold is soft, spongy, or visibly rotted, the threshold itself isn't the problem — the frame needs repair first. A carpenter can assess whether the rot is surface-level (can be scraped and sealed) or deep (requires frame replacement). If the floor on either side of the threshold is uneven or slopes the wrong way, a professional can determine whether shimming will work or whether the subfloor needs attention.

If you're uncomfortable using a pry bar or power tools, or if the threshold is stuck so firmly that you can't budge it after 20 minutes of careful work, a handyperson can remove and install it in an hour or two. The job itself is straightforward, but it does require some physical effort and basic tool skills.

Frequently Asked Questions

Can I install a new threshold without removing the old one?

No — the old threshold has to come out first. Installing a new one on top creates a trip hazard, prevents the door from closing properly, and traps moisture underneath where it causes rot. Removal takes 15 to 30 minutes and is worth doing right.

What if water still leaks under the door after I replace the threshold?

Check that the threshold is level and that the caulk along both sides is continuous with no gaps. If water still gets through, the door itself may not be closing tight, or the frame may be warped. A professional can check the door alignment and frame condition.

Do I need to paint or stain a new wood threshold?

For exterior doors, yes — sealing the wood with stain or sealant protects it from weather and extends its life. For interior doors, it's optional and depends on whether you want it to match your trim or flooring.

How long does a composite threshold last compared to wood?

A wood threshold on an exterior door typically lasts 5 to 10 years before rot sets in. A composite threshold in the same location lasts 15 to 20 years with minimal maintenance, making it a better long-term choice despite the higher upfront cost.

What's the difference between a threshold and a sill?

A sill is the horizontal part of the frame itself that the threshold sits on. A threshold is the separate strip you install on top of the sill to seal and protect it. If your sill is damaged, you may need a carpenter; if your threshold is damaged, you can replace it yourself.