Door weatherstripping

Find the leak first

• The paper test. Close the door on a sheet of paper. If it slides out easily, the seal is not touching at that spot. Repeat around the frame.
• The light test. At night, with a light on outside, look for light around the edges from inside.
• Moving air. On a windy day, a damp hand or the smoke from an incense stick shows where air comes through.
• The bottom corners. Most drafts come in at the two bottom corners, where the frame seal meets the door sweep.

Types of weatherstripping

Kerf-in compression seals press into a slot, called a kerf, in the door frame. Most modern steel and fibreglass doors use these; they last the longest and are easy to replace. Foam tape sticks on and is the cheapest, but compresses and wears out quickly. V-strip is a folded plastic or metal strip that springs against the door edge. Door sweeps and door bottoms seal the gap at the threshold; U-shaped bottoms slide onto the bottom of the door. Corner pads fill the small gap at the bottom corners.

Rain, not just cold

On the West Coast, the bigger problem is often wind-driven rain rather than cold. A worn door bottom or a threshold that no longer meets the door lets water in at the bottom corners, where it soaks the sill and the bottom of the frame and starts rot. A good door bottom, sealed corner pads and a properly adjusted threshold keep out water as well as drafts. If the frame is already soft, see wood rot repair.

How to replace kerf-in weatherstripping

1. Open the door and pull the old strip straight out of the slot in the frame. Take a piece to the store to match the profile.
2. Clean the kerf of dirt and old bits of seal.
3. Starting at a top corner, press the new strip's flange into the kerf, working along the head and down each side. Cut it slightly long; it compresses into place.
4. Close the door and check that it latches without forcing. A seal that is too thick makes the door hard to close.
5. Replace the door sweep or bottom, and fit corner pads if the old ones are worn.

When new weatherstripping will not fix it

If the gap is uneven, the door itself may be the problem: a warped door, sagging hinges or a frame out of square. Tightening hinge screws, adjusting the strike plate, or raising an adjustable threshold fixes many of these. Rot at the bottom of the frame is common on older exterior doors; see door frame repair, or exterior door installation cost if the door is past saving.

What it costs

Doing every exterior door in one visit is much cheaper per door than one at a time, and the same visit can adjust hinges, strike plates and thresholds.