Tension-seal V-strip weatherstripping — also called spring bronze or pile weatherstripping depending on the material — is one of the most durable solutions for sealing the sliding channels of double-hung windows. Unlike foam tape, which compresses under a stationary sash, V-strip is designed for surfaces that move. The folded strip sits inside the channel; as the sash slides past, the strip's spring tension maintains contact, creating a continuous seal.
Older wooden window construction, as seen in this heritage building, typically uses sliding sash channels where V-strip weatherstripping is most effective. (Wikimedia Commons, CC BY-SA 4.0)
Types of V-Strip Material
Spring Bronze
Spring bronze V-strip is the material historically used in older Canadian homes and remains available at building supply stores. It is durable, does not degrade from UV exposure, and can last decades in a properly maintained window. The installation process requires cutting, fitting, and nailing or stapling the strip into the channel — a more involved process than self-adhesive options, but the result is longer-lasting.
Plastic (Vinyl) V-Strip
Self-adhesive vinyl V-strip is widely available and easier to install. It attaches to the channel with a peel-and-stick backing. Vinyl is less durable than spring bronze and more susceptible to becoming brittle in very cold temperatures. In a climate like central Ontario or Alberta in January, low-grade vinyl strips may lose their spring tension after two or three winters.
Pile (Brush) Weatherstripping
Pile weatherstripping uses a row of fine fibres to create a soft seal. It is common in aluminum window frames and in situations where a sash slides in two directions. For wooden heritage windows with irregular channels, pile can accommodate minor surface variations better than rigid V-strip.
Where V-Strip Goes in a Double-Hung Window
In a standard double-hung window, there are four vertical channel surfaces — two for the upper sash and two for the lower sash. The V-strip is installed in these channels, oriented so that the open edge of the V faces outward (toward the exterior) to create pressure against the sash as it moves.
- Lower sash channels: The two grooves between the parting bead and the inside stop on each side of the frame
- Upper sash channels: The two grooves between the parting bead and the outside stop
- Meeting rail: Where upper and lower sashes meet — foam tape or interlocking metal seals are generally more suitable here than V-strip
Preparing Older Window Channels
Heritage window channels often have accumulated paint layers, old weatherstripping remnants, or surface roughness from decades of use. Before installing V-strip, the channel must be clean and smooth enough for the sash to slide freely.
- Remove the inside stop on one side using a putty knife and pry bar. Work carefully to avoid splitting old wood. Set the stop aside — it will be reinstalled.
- Lift the lower sash out of the frame. This gives clear access to the full channel.
- Scrape paint drips and rough spots from the channel surfaces with a chisel or scraper.
- Sand the channel lightly with 120-grit sandpaper to create a smooth running surface.
- Wipe the channel with a dry cloth.
Do not paint the channel before reinstalling the sash. Paint adds thickness and friction, and if applied to the channel where V-strip will sit, it reduces adhesion for self-adhesive products and creates an uneven surface for spring bronze.
Installing Spring Bronze V-Strip
Spring bronze V-strip for a standard 1.5-metre-tall window comes in rolls or pre-cut lengths. Cut the strip to match the full height of the channel — from the sill to the top of the lower sash travel, or from top to bottom for the upper sash channel.
Place the strip in the channel with the open edge of the V facing the exterior (the edge that will press against the sash). Nail or staple the strip along its flat spine at approximately 5 cm intervals using a staple gun or small tacks. The strip should lie flat against the channel surface with the V-fold protruding into the channel space.
After installing the strip, run a screwdriver or putty knife along the V-fold to open it slightly — this increases the spring tension and improves the seal. Test by sliding the sash through its full travel. There should be slight resistance from the strip but the sash should move without binding.
Common Problems and Adjustments
Sash Binds After Installation
If the sash is difficult to move after V-strip installation, the strip may be too wide for the channel, or the V-fold may be opened too far. Try flattening the fold slightly by pressing it with a putty knife. If the channel itself is too narrow, the strip may need to be trimmed to a narrower width.
Strip Does Not Contact Sash
If the V-strip is too flat, it will not press against the sash and will not seal. Open the fold further using a screwdriver. Spring bronze may need to be re-tensioned if it has been compressed for a long time.
Gaps at Top or Bottom of Travel
Ensure the strip runs the full length of the channel, not just the active travel zone of the sash. Gaps at the ends of the channel allow air to bypass the seal even if the middle section is well fitted.
Reinstalling the Sash and Stop
After fitting the V-strip, reinstall the sash in the frame. For old windows with sash weights and cords, this involves routing the cord through the pulley and connecting it to the sash before lowering it into place. Reinstall the inside stop, pressing it against the sash firmly enough to prevent rattling but loosely enough that the sash slides without friction. Nail the stop in place with finish nails.
Durability in Canadian Conditions
Spring bronze V-strip installed properly in a cleaned channel typically lasts 10 to 20 years before needing replacement or re-tensioning. Plastic V-strip lasts 5 to 10 years in moderate conditions; less in climates with extreme cold or high UV exposure. Annual inspection at the start of heating season can catch deterioration before it results in significant heat loss.