How to Replace Window Weatherstripping

Types of weatherstripping

Not all weatherstripping is the same. The three most common types for windows are V-seal, foam tape, and felt. Each has trade-offs in cost, durability, and ease of installation.

V-seal (tension strip) is a folded strip of vinyl or metal that springs open to fill gaps. It is the most durable option and lasts three to five years. It compresses and rebounds thousands of times without losing its shape. It works in the channels of double-hung and sliding windows and is nearly invisible when installed.

Foam tape is the cheapest option and the easiest to install. Peel the backing and stick it on. But foam compresses permanently under sustained pressure, so it loses its seal within one to two years. It works as a temporary fix but is not a long-term solution.

Felt is the oldest type of weatherstripping. It is inexpensive and easy to cut but wears out quickly, absorbs moisture, and looks shabby. It is best suited for low-traffic windows like attic or basement windows that rarely open.

For most homeowners, V-seal is the right choice. It costs a few dollars more than foam tape and lasts three times as long.

Signs your weatherstripping needs replacing

The most obvious sign is a draft. If you feel cold air near a closed and locked window on a windy day, the weatherstripping is not sealing. Hold a lit incense stick near the window edge and watch the smoke. If it moves horizontally, air is getting through.

Physical damage is the other indicator. Open the window and look at the strip. Compressed foam that does not spring back is done. Cracked or brittle vinyl has lost its flexibility. Missing sections leave a gap that nothing can seal except new material.

The window itself tells you too. If you can rattle the sash when the window is closed and locked, there is play between the sash and frame that weatherstripping should be filling. A properly sealed window feels solid and quiet when closed.

V-seal installation tips

The key to a good V-seal installation is orientation. The fold of the V should face the outside of the house. When the window sash closes, it compresses the V, and the two legs of the V press against the sash and the channel to create a seal. If you install it backward, the sash pushes the V flat instead of compressing it, and you get no seal.

Work in small sections when peeling the adhesive backing. Peeling the entire backing at once lets the strip twist and stick to itself, which wastes material. Six-inch sections keep you in control.

Press firmly along the entire length after installation. Run your thumb or a flat tool along both edges of the strip. Any section that is not fully adhered will peel away over time, especially in channels where the sash slides past repeatedly.

Cut the strip slightly long and trim to fit. A quarter inch of excess is easy to trim with scissors. A quarter inch of gap at the end lets air through and defeats the purpose.

Measuring and cutting

For double-hung windows, you need to weatherstrip the channels on both sides of the lower sash, the top of the upper sash, and the meeting rail where the two sashes overlap. Measure each section individually. Do not assume both sides are the same length. Older homes settle, and the channels may differ by half an inch or more.

For sliding windows, measure the top and bottom tracks and both vertical edges of the sliding panel. The fixed panel usually does not need weatherstripping because it sits in a compression gasket set at the factory.

A 17-foot roll of V-seal is enough for one to two standard windows. Buy one extra roll so you do not have to stop mid-project for a hardware store run. Unused V-seal stores indefinitely in a drawer.