How to Replace a Door Threshold

Pity the poor wooden threshold. That stomped-on, scuffed-up, taken-for-granted plank bakes in the sun, gets soaked by the rain, and endures the grit from every shoe that tromps in or out of the house. Without regular attention—an occasional lick of paint and some caulking—sooner or later that wood’s a goner, and the underlying framework isn’t far behind.

It’s best to start replacement work early in the day, so there’s time to fix any problems that come to light after the old threshold is out. A rotten subsill, punky joist ends, or a termite-riddled rim joist can stretch this two-hour job into a full day’s labor.

Here’s a step-by-step tutorial on how to install a door threshold.

How to Replace a Door Threshold in 9 Steps

Step 1: Know the Parts That Make Up the Exterior Door Threshold

Click ”enlarge this image” to view illustration labels.

Key details to note: The threshold itself is angled — typically at 5 to 7 degrees — to pitch water away from the door. As TOH project manager Zack explained during a recent build, there’s a flat spot where the door sits, plus a small rabbet designed to keep water from creeping uphill via surface tension and running under the door. The horn of the threshold extends beyond the opening so the exterior casing can land right on top of it. On the interior side, a chamfer — that angled edge — prevents you from stubbing your toe going out the door.

Pro Tip: TOH general contractor Tom Silva warns that water is the threshold’s biggest enemy: “Water comes down and hits the ground in front of the door, splashes back up, gets under the threshold, hits the sill of the house and rots it.” That’s why understanding how each part works together to shed moisture is critical before you start the replacement.

Step 2: Prep With Replacement at the Ready

Measure the length, width, and thickness of the old threshold, and have a replacement with a similar pro­file on hand. It should be an inch or two longer than the distance between the door casing’s outside edges so you can trim it for an exact fit later on.

Remove the storm door and any weatherstripping attached to the threshold.

Tip: You’ll spend a lot of time kneeling on the outside of the house. Place rubber mats on the porch, as Tom did, or invest in a good pair of knee pads.

Pro Tip: Tom Silva, TOH general contractor, explains that a laminated replacement threshold is actually preferable to a solid one: “Your original threshold is one solid piece of oak. This new threshold is made up of a series of strips of oak that are glued together to make the dimension of your existing threshold… It’ll definitely wear as well. This will actually respond better to the weather. It’s more stable.”

Step 3: Remove the Old Threshold

Fit a wood-cutting blade, at least as long as the old threshold is deep, into a reciprocating saw.

Slice across the wood in two places, about 10 inches from each jamb. Hold the blade so its teeth are nearly parallel to the surface, and watch its tip so you don’t cut the flooring.

Stop sawing as soon as you feel the blade cut through the threshold. Wait until the blade stops moving before lifting it out of the kerf.

Pro Tip: TOH general contractor Tom Silva recommends inserting a chisel under the threshold first to create a gap: “I need to get my saw blade in here to cut the nails that are holding this threshold down and in.” Once the nails are cut, make your crosscuts on a bevel — as Tom explains, “I cut those two cuts on a bevel, that should make this piece slide right out.”

Step 4: Pry Out Exterior Board & Treat

Stick a flat bar (aka pry bar) between the threshold and the subsill and pry up the center section. Wiggle the ends away from the jambs, if you can, or split them with a hammer and chisel and take them out piece by piece. Use patience and finesse, not brute force; you don’t want to damage the ends of the door stops.

Pry off the toekick (the exterior board below the threshold), and probe the wood underneath for signs of decay.

Replace any rotten wood you find, and spray it all with a borate solution like Bora-Care to prevent rot and repel termites.

Step 5: Install the Rubber Seal

A layer of flashing on the subsill prevents water from reaching the framing below. Tom uses Vycor Plus, a rubbery, self-adhering membrane that he cuts to fit between the jambs and a few inches wider than the subsill. The flashing goes over the subsill, adhesive side down, with just enough overhang in front to cover the top edge of the toekick.

After smoothing out the membrane, Tom grabs the edge closest to the inside of the house and rolls it over onto itself, forming a small dam against water infiltration.

Step 6: Lay Out the Notch for the New Threshold

The ends of the new threshold have to be notched to fit around both door jambs. This creates a “horn” that extends under the casing. First, measure the width of the right-hand casing, then hook the tape on the threshold’s back right-hand corner and transfer that measurement to the threshold’s back edge.

Next, measure the width of the jamb and stop, hook the tape on the same corner, and transfer the measurement to the end of the stock. Use a square to draw a perpendicular line from each mark until both lines intersect.

Pro Tip: When replacing a threshold, you’ll spend a lot of time kneeling on the outside of the house. Place rubber mats on the porch or invest in a good pair of knee pads to save your knees during the layout and fitting process.

Step 7: Cut Out the Notch By Measuring Jamb to Jamb

Cut along the layout lines with a jigsaw or circular saw; finish circular-saw cuts with a handsaw.

To mark the cuts for the left-hand notch, measure the width of the opening from jamb to jamb, then hook the tape on the cut-out notch and transfer that measurement to the threshold’s back edge.

Mark the width of the jamb and stop on the threshold’s left end, join the marks with a square, and cut out the notch, as shown.

Trim the horns flush with the edges of the casing. Sand the threshold with 120-grit paper and spray it with borate.

Step 8: Install the Threshold

Slip the notched threshold into position under the door stops, then nudge it into place by tapping a hammer on a wood block against the threshold’s edge.

Change the block’s position so neither end of the threshold gets too far ahead of the other.

When it’s tight to the subfloor, slide pairs of shims—ones cut from cedar shingles are best—under the center and both ends of the threshold, but not under the horns.

Arrange the shims so the thin end of one rests on the fat end of the other. That way, as you tap on the fat end, the threshold will lift without tilting.

When the threshold is tight against the door stops and casing, snap the shim ends off flush with the subsill.

Pro Tip: Tom Silva, TOH general contractor, recommends leveling the subfloor before setting the threshold: “The sub floor is not level and it’s also crooked. Not surprising with an old house, but we also wanna raise the entire door up about a half an inch.” To check, he places a piece of two-by-four across the opening with a level on top, then shims until it reads true before scribing and trimming the filler to fit.

Step 9: Seal with Foam

Squirt expanding foam sealant under the threshold to hold it in place and plug any air gaps. Immediately put the toekick up under the flashing and tight against the underside of the threshold, and screw it to the subsill.

Run a bead of sealant between the threshold and each door stop.

Finally, protect the wood with deck paint or several coats of spar varnish.

Finishing Advice: When it comes to protecting the new threshold, Tom Silva recommends: “Put a coat of deck paint on it, if you like a color, or you can use a polyurethane or a Marine finish, but make sure it has a UV protector in it.”

Pro Tip: Tom Silva, TOH general contractor, explains why this approach works: “The expanding foam, the shim shingles underneath holds the threshold tight against the jam, and also the row of caulking” around the edges locks everything in place—no screws or nails needed to secure the threshold itself.

Tools

Pro Tip: TOH general contractor Tom Silva advises measuring your old threshold before heading to the store: “Measure the length, width, and thickness of the old threshold, and have a replacement with a similar profile on hand. It should be an inch or two longer than the distance between the door casing’s outside edges so you can trim it for an exact fit later on.”