How to weatherstrip a back door — the four kinds and where each goes

A back door is the most-leaked exterior door in a typical house, because it gets the least attention. Front doors get the weatherstripping budget because they’re visible; back doors get the cold air. Twenty dollars and two hours fixes this.

The four kinds of weatherstrip and where each goes

Most “weatherstripping” sold at hardware stores is one of four products, each optimized for a different gap:

1. V-strip (also called tension seal) — for the door stops (the part of the jamb the door closes against). V-strip is plastic or metal folded into a V, sticking to one face of the stop and pressed flat by the door each time it closes.
2. Compression bulb / foam tape — for the head jamb (the top of the door frame) and stop face. Best where the gap is consistent.
3. Door sweep — for the bottom of the door. A flexible blade (rubber, vinyl, or brush) attached to the lower edge that drags across the threshold.
4. Magnetic stripping — for the latch-side door stop. Like a refrigerator door, the magnetic strip clings to the door’s steel edge for the tightest seal. Premium option.

You will use three of the four on any given back door. Most installs use V-strip + sweep + magnetic.

Step 1: identify the gaps

Close the door at night. Turn off the interior lights. Have a helper shine a flashlight along all four edges from outside. Where you see daylight, you have a leak.

The most common leaks:

• Bottom: ~70% of installs. Sweep is missing, damaged, or doesn’t reach.
• Latch side stop: ~50%. V-strip missing or compressed flat.
• Hinge side stop: ~30%. V-strip missing.
• Head jamb: ~20%. Often from a settled house.

Step 2: install V-strip on the stops

Measure the length of each door stop (the vertical strips of the jamb that the door closes against, plus the horizontal head stop above the door). Cut V-strip to match each length.

The V-strip has a peel-and-stick adhesive on one face. Peel a foot of backing, press the V-strip onto the stop with the open face of the V pointing out (toward the door). Continue pressing as you peel.

The point of the V is in the corner where the stop meets the jamb. When the door closes, it presses on the open face of the V and folds it flat — sealing the gap.

For a back door, hinge side and head get the V-strip. The latch side will get the magnetic strip (see step 4).

Step 3: install the door sweep

Measure the width of the door at its bottom edge. The sweep should be 1/16” shorter than that — you want it to fit just inside the door width.

Cut the sweep to length. Most sweeps are aluminum housing with a vinyl or rubber blade — cut the housing with a hacksaw, then trim the blade with scissors.

Set the sweep against the inside (interior face) of the door, flush with the bottom edge, with the blade dragging on the threshold. Mark the screw holes with a pencil. Drill pilot holes (1/16” smaller than the screws). Screw the sweep on.

Open and close the door. The blade should drag lightly on the threshold across the full width. If it drags hard at one end, the sweep is mounted at an angle; loosen one end and adjust.

If the blade doesn’t reach the threshold at all, the door has shrunk (common in dry winters). Buy an adjustable sweep — it has slotted holes that let you slide it down 1/4” or more.

Step 4: install magnetic strip on the latch-side stop

Magnetic stripping is for the latch side of the stop only — the side that pulls against a steel door. It needs steel to cling to; it won’t work on a fiberglass or wood door.

Measure the length of the latch-side stop. Cut the magnetic strip to match. Peel and stick, the same as V-strip, but with the magnetic face out.

When the door closes, the magnet pulls the door tightly against the stop, giving a much better seal than V-strip alone.

Step 5: corner pads

The two corners where the stops meet (top corners of the door frame) are where most installs leak even after stripping. Buy a set of foam corner pads — they’re little triangles, $5 for a 4-pack — and stick one in each top corner where the stops meet.

This is the step that gets you from “noticeably better” to “completely sealed.”

What can go wrong

• Door won’t close: too much stripping; you can’t compress it all. Remove the V-strip from the hinge side; that’s usually the culprit.
• Door rubs at one corner: door is out of square in the frame. Adjust the hinges; don’t try to fix it with stripping.
• Stripping falls off in summer: heat is melting the adhesive. Buy higher-temp stripping (“commercial grade”) and re-install.
• Cold spot at the bottom corner: corner pad is missing or sweep doesn’t reach the corner. Add or extend.

Why back doors specifically

Front doors usually have a vestibule, a storm door, or both. They also tend to be the same age as the house. Back doors are often the cheapest pre-hung steel unit the builder could find, with the cheapest adjustable sweep, and they’ve been kicked open by hands full of grocery bags for fifteen years. They leak.

The Society maintains that a back door is the one you walk through every day, and the most-used door in your house deserves the best weatherstripping. The fact that it’s hidden from the street is not a reason to skip the job.

The Anchorage Vestibule approach

The Society’s collection includes the Anchorage Vestibule, a 1965 Alaska Railroad inner door with triple-stage weatherstripping (compression, magnetic, sweep) that has worked perfectly for 60 years. If you live somewhere cold, the right answer to back-door insulation is not better weatherstripping on one door — it’s a vestibule. A second door, six feet inside the first, with even modest stripping, beats any single-door installation. Consider the architecture, not just the hardware.