Steps // How to Replace a Threshold
1 ×

Replacing a Threshhold

Step One // How to Replace a Threshold

Replacing a Threshhold

Replacing a Threshhold

Click ''enlarge this image'' to view illustration labels.

2 ×


Step Two // How to Replace a Threshold


before you start
Photo by Reena Bammi

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.

3 ×

Remove the Old Threshold

Step Three // How to Replace a Threshold

Remove the Old Threshold

Cut out the old one
Photo by Reena Bammi

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.

4 ×

Pry Out & Treat

Step Four // How to Replace a Threshold

Pry Out & Treat

Remove the pieces
Photo by Reena Bammi

Stick a flatbar 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.

5 ×

Install the Flashing

Step Five // How to Replace a Threshold

Install the Flashing

Installing sill flashing
Photo by Reena Bammi

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.

6 ×

Lay Out the Notch

Step Six // How to Replace a Threshold

Lay Out the Notch

Lay out the notch
Photo by Reena Bammi

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.

7 ×

Cut Out the Notch

Step Seven // How to Replace a Threshold

Cut Out the Notch

cut out the notch
Photo by Reena Bammi

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.

8 ×

Install the Threshold

Step Eight // How to Replace a Threshold

Install the Threshold

Coax it in
Photo by Reena Bammi

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.

9 ×

Seal with Foam

Step Nine // How to Replace a Threshold

Seal with Foam

Foam it
Photo by Reena Bammi

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.


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