Exterior Door Weatherstripping Replacement: Sweep, Jamb and Threshold

Three seals fail three different ways; the hinge is often the real culprit, and a New York winter adds ice at the sill to the list.

Exterior Door Weatherstripping Replacement: Sweep, Jamb and Threshold

An exterior door seals in three places, and they fail differently. The
jamb weatherstrip runs up both sides and across the head and is squeezed by
the door as it closes. The sweep or shoe runs along the bottom edge of the
door and drags across the threshold. The threshold itself, with its gasket,
is what the sweep lands on. A draft at the floor, frost on the inside of
the door in January, or daylight showing at a corner each point to a
different one of the three, and replacing the wrong one is the usual reason
a new seal changes nothing.

Find the Failure Before Buying Anything

Close the door on a strip of paper at several points around the frame.
Where it slides out without resistance, the seal is not touching. Do it at
the hinge side, the latch side, the head and the sill, because a door that
seals at the latch and gapes at the head is telling you the door is out of
square rather than that the weatherstrip has worn. Then look at the seal
itself: a compressed foam or vinyl strip that no longer springs back, a
kerf-in strip that has pulled out of its slot, a sweep with a torn fin, or
a threshold gasket that has hardened and cracked. On a cold windy day a
hand along the edges finds the rest, and a blower door
test with a smoke pencil finds it precisely, though nobody needs one to
diagnose a door.

Before any seal is replaced, check the hinges and the strike. A door
that has sagged on its hinges rubs at the top of the latch side and gaps at
the bottom of the hinge side, and no weatherstrip is thick enough to close
a gap that changes along its length. Replacing one hinge screw per hinge
with a longer one that reaches the framing, and moving the strike plate so
the door pulls tight against the stop, is the first step and often the
only one needed.

The Jamb Seal

Modern pre-hung doors carry a kerf-in seal: a foam or vinyl bulb with a
barbed fin that presses into a slot cut in the stop. Replacement is a
matter of pulling the old strip out of the kerf and pressing a new one in,
and the only decision is the profile, which should match the depth of the
gap between the door and the stop. Older wood doors have no kerf; they take
a surface-mounted strip nailed or screwed to the stop, either a vinyl bulb
in a metal or wood carrier, or spring bronze, a folded metal strip that the
door compresses on closing and which outlasts every foam alternative. Steel
doors sometimes take a magnetic strip in the kerf, the same idea as a
refrigerator gasket, which needs a steel skin to work.

Self-adhesive foam tape is the product sold most and the one that fails
soonest. It fills a gap well for one season, then compresses permanently
and stops sealing, and its adhesive lets go in the cold. It has a place as
a stopgap on a door that is about to be replaced, and nowhere else.

The Sweep and the Shoe

The bottom of the door is sealed either by a sweep, a strip screwed to
the inside face of the door with a fin or brush that drags on the
threshold, or by a door shoe, a U-shaped channel that fits over the bottom
edge of the door and carries a bulb underneath. A sweep is the easier
retrofit because the door stays on its hinges; a shoe seals better because
the bulb compresses against the threshold rather than dragging over it, and
it protects the bottom edge of a wood door from water. On a door that
opens over carpet, an automatic drop seal, which lowers a gasket only as
the door closes, avoids the drag.

The gap the sweep must close is set by the threshold height, and a sweep
set too low binds and tears; set too high it seals nothing. Adjustable
thresholds, with screws that raise or lower a cap, exist to tune this gap,
and they drift over the years as the screws back out, which is one more
thing to check before replacing a sweep that seems to have failed.

The Threshold

The threshold gasket, the rubber or vinyl insert in the threshold’s
channel, does its job against the door shoe or the bottom edge. It hardens
and cracks with age and with the salt and sand that a New York winter
brings in, and it is replaced by pulling the old insert out of the channel
and pressing a new one in, in the same way as a kerf seal. A threshold that
has rotted, moved, or lost its seal to the sill underneath is a bigger job,
since water has been getting under it, and at that point the door frame is
the question rather than the weatherstrip.

Winter, Ice and the Storm Door

A New York door has two problems the seal manufacturers did not plan
for. Ice at the sill: snowmelt that runs down the door face freezes in the
threshold channel and lifts the gasket or freezes the sweep to it, so that
the first opening of the morning tears the fin. A shoe with a drip cap,
which throws water off the face of the door before it reaches the
threshold, is the answer, along with clearing the sill rather than forcing
the door. And condensation: an exterior door that is cold on the inside
face in January collects frost the way a cold
window does, and a seal that leaks air makes the surface colder still.
Adding a storm door changes the picture, since it creates a still air layer
that keeps the main door’s inside face warmer, and the same logic makes
an interior storm panel work on a window.

Where It Sits in the Bigger Job

A door is a small leak in a big envelope. The attic
hatch, the knee wall door and the
garage door bottom seal each let more air through
than a front door, because the pressure driving the air is greatest at the
top and bottom of the house, and the air-sealing survey that a
weatherization program or a contractor performs
will rank them that way. The reason to do the door anyway is that it is the
leak you feel, at the floor, where you stand, and it is an afternoon’s work
on the homeowner side of the line. It belongs in the
air-sealing pass before the heat pump, not
instead of it, and well ahead of any decision about
replacing the door or the windows.

Frequently Asked Questions

How do I know which part of the door seal has failed?

Close the door on a strip of paper at the hinge side, the latch side, the head and the sill. Where it slides out freely, that seal is not touching. A gap that varies along one edge points to hinge sag rather than to the weatherstrip.

Should I replace the weatherstripping or adjust the door first?

Adjust first. A sagging hinge or a strike plate set too far out leaves a gap no weatherstrip can fill, and a longer hinge screw into the framing plus a moved strike plate fixes many doors that seemed to need new seals.

What type of weatherstripping lasts longest on an exterior door?

Spring bronze on a wood door outlasts every foam product. A kerf-in bulb on a pre-hung door is easy to replace and lasts well. Self-adhesive foam tape compresses and lets go within a season or two.

Sweep or door shoe?

A sweep is the easier retrofit because the door stays on its hinges. A shoe seals better, since its bulb compresses against the threshold instead of dragging, and it protects the bottom edge of a wood door. Over carpet, an automatic drop seal avoids the drag altogether.

Why does my new sweep tear or bind?

It is set too low against the threshold. Check whether the threshold has an adjustable cap that has drifted, set its height first, then fit the sweep so that the fin just touches.

Does replacing door weatherstripping save much energy?

A door is a small share of a house’s leakage next to the attic and basement bypasses, so the number on a blower door test barely moves. The gain is comfort at floor level, and an end to ice and frost at the door. Do it as part of an air-sealing pass, not instead of one.

Can I do this myself?

Yes. A kerf strip, a sweep and a threshold gasket are hand-tool jobs on the homeowner side of the weatherization line. A rotted threshold or a frame that has moved is where it stops being one.

Does a storm door replace the need for weatherstripping?

No. A storm door adds a still air layer that keeps the main door warmer and reduces frost on its inside face, but the main door’s seals still carry the air seal, and both doors need their own.