How to Fix a Drafty Window: Weatherstripping, Caulk, Film, and Storm Windows

A drafty window is costing you money every hour the heat runs. The Department of Energy estimates that air leaks through windows and doors account for 25 to 30 percent of a home’s heating and cooling costs.

A drafty window is costing you money every hour the heat runs. The Department of Energy estimates that air leaks through windows and doors account for 25 to 30 percent of a home’s heating and cooling costs. The good news: fixing a drafty window is one of the highest-return DIY jobs you can do. Most repairs cost $5 to $50 per window in materials.

The approach depends on where the draft is coming from. This guide walks through finding the source and applying the right fix.

What You Need

• Rope caulk (removable weatherseal) — press-in putty for sash gaps, peels off in spring
• V-strip weatherstripping — durable spring bronze or plastic for sash channels
• Silicone caulk exterior — for sealing the fixed frame to the house exterior
• Window insulation film kit — shrink-film creates an insulating dead-air layer
• Foam backer rod — for filling large gaps before caulking
• Draft snake or door bottom seal — for drafts at the window sill

Step 1: Find the Source of the Draft

Before buying materials, identify exactly where the air is entering. Different locations require different fixes.

Common draft locations on double-hung windows:

Location	Cause	Fix
Between upper and lower sash (meeting rail)	Worn weatherstrip or warped sash	Rope caulk or V-strip
Along sash sides (in the channel)	Worn or missing V-strip	New V-strip weatherstripping
Between window frame and house wall (exterior)	Failed caulk or missing sealant	Exterior silicone caulk
At the sill (bottom of lower sash)	Worn sill seal	Foam compression strip
Through the glass	Failed double-pane seal (fogging)	Window replacement

The incense stick test: Light a stick of incense and move it slowly around the full perimeter of the window — all four sides, the meeting rail, and the corners. Watch for smoke movement. Mark each location where you detect a draft.

Do this on a cold, windy day for the best results. Even a slight breeze outside amplifies infiltration and makes small leaks visible.

Step 2: Seal the Fixed Frame with Exterior Caulk

The joint between the window frame (the fixed outer frame bolted to the house) and the surrounding siding or trim is a common air leak point. This caulk line fails over years from UV exposure and thermal cycling.

Inspect from outside:

1. Look around the entire perimeter of the window exterior — all four sides where the window trim meets the siding.
2. Probe existing caulk with a putty knife. If it crumbles, pulls away, or has visible gaps or cracks, it needs to be replaced.
3. Check the joint between the window sill and the siding below.

Re-caulk the exterior frame:

1. Remove all old caulk with a putty knife or caulk removal tool. Getting clean edges is critical — new caulk does not bond well over old.
2. Clean the joint with a damp cloth and let dry.
3. For gaps over 1/4 inch: insert foam backer rod into the gap first. This fills the void and gives caulk the right depth (caulk should be slightly concave, not filling the entire gap).
4. Apply silicone or paintable polyurethane caulk in a steady bead along the joint.
5. Tool smooth with a wet finger or caulk tool within 5 minutes.
6. Allow to cure fully before painting (check label — silicone usually takes 24 hours).

Interior frame caulking: Check the joint between the interior window trim and the drywall. A bead of latex caulk here reduces interior infiltration and is painted over easily.

Step 3: Replace V-Strip Weatherstripping in the Sash Channels

The sash channels on a double-hung window — the tracks the upper and lower sash slide in — are a major source of air infiltration. V-strip weatherstripping (also called tension seal) presses into the channel and creates a seal against the sash as it slides.

How to install V-strip in sash channels:

1. Raise the lower sash as high as it goes.
2. Cut V-strip to the length of the channel (top to bottom).
3. Press the V-strip into the channel with the open side of the “V” facing out toward the sash. The strip should sit flat against the channel wall.
4. Use a putty knife or the back of a spoon to seat the strip firmly. It should be snug enough to create resistance but not so tight that the sash won’t slide.
5. Lower the sash and test: it should move smoothly while the strip presses against it.
6. Repeat on the other channel side.

For the upper sash channels: lower the upper sash and install V-strip in the upper section of the channel in the same way.

Spring bronze V-strip lasts 20+ years and outperforms foam or plastic versions. It is harder to install but worth it on wood windows you plan to keep long-term.

Step 4: Seal the Meeting Rail with Rope Caulk

The meeting rail is where the upper and lower sash meet in the middle of a double-hung window. This horizontal gap is often the biggest source of air infiltration. When the window is closed, the two sashes should press together firmly — but over time, sash warping and worn weatherstripping leave a gap.

Rope caulk is the fastest fix:

1. Clean the meeting rail surfaces with a dry cloth.
2. Pull a length of rope caulk from the roll and press it into the gap at the meeting rail.
3. Press firmly with your finger along the full length of the rail.
4. Check both the interior and exterior faces of the meeting rail — apply rope caulk to both if needed.

Rope caulk remains pliable all winter and peels off cleanly in spring when you want to open the window. One roll ($4 to $7) typically covers 5 to 6 windows.

For a permanent fix: Install a kerf-in foam compression strip along the meeting rail instead. This requires a thin kerf cut into the rail edge with a router, then a foam strip is pressed in. It compresses when the window closes and seals the gap permanently.

Step 5: Add Compression Foam at the Sill

The bottom of the lower sash and the window sill is another high-infiltration zone. Closed-cell foam tape provides a compression seal here.

1. With the window open, clean the sill surface.
2. Apply self-adhesive closed-cell foam tape along the full width of the sill in the path the lower sash presses down on when closed.
3. Close the window — it should compress the foam and create a tight seal.
4. Foam tape typically lasts 2 to 5 years before compression set causes it to lose effectiveness.

Step 6: Apply Window Insulation Film (Seasonal)

Window insulation film kits create a second pane effect by taping a thin plastic film over the entire interior window opening. The dead air space between film and glass insulates significantly better than bare glass.

Installation:

1. Clean the window frame thoroughly — the double-sided tape adheres best to clean, dry surfaces.
2. Apply the double-sided tape from the kit around the full perimeter of the window frame (not the glass — the frame).
3. Cut the film slightly larger than the opening and press it onto the tape.
4. Use a hair dryer on low heat, moving back and forth across the film. The heat shrinks the film taut and eliminates wrinkles.
5. Trim any excess film at the edges with scissors.

The installed film is nearly invisible from inside and does not significantly distort the view. It cannot be opened, so apply this fix only to windows you don’t need to open in winter.

Remove in spring by peeling off the tape — this may pull paint if the frame paint is old or peeling. Test a corner first.

Cost: Most window film kits cover 3 to 5 windows and cost $10 to $25.

Step 7: Install or Replace Storm Windows

Storm windows are the most effective solution for single-pane windows. They add a second air gap outside the existing window, dramatically reducing both infiltration and heat loss through the glass.

Interior storm windows (acrylic panels that snap into the existing window frame from inside):

• No exterior ladder work required
• Effective for apartments or rental properties where exterior work isn’t permitted
• $25 to $75 per window depending on size

Exterior storm windows (aluminum or wood-framed second windows installed outside the existing window):

• More durable and effective than interior films
• Can be opened to allow ventilation (triple-track storm windows)
• $75 to $250 per window installed DIY; $150 to $400 professionally installed

For homes with original single-pane wood windows that are otherwise in good condition, storm windows are a better investment than full window replacement because they preserve the historic window while dramatically improving performance.

Comparing the Fixes by Cost and Effort

Fix	Cost Per Window	Time	Permanence
Rope caulk (meeting rail)	$1–$2	5 minutes	Seasonal (remove in spring)
Window film kit	$3–$8	20 minutes	Seasonal
Foam compression tape (sill)	$2–$5	10 minutes	2–5 years
V-strip weatherstripping	$5–$15	30–45 minutes	10–20 years
Exterior caulk (frame)	$3–$8	20 minutes	10–20 years
Interior storm window	$25–$75	20 minutes	Semi-permanent
Full storm window	$75–$250	1–2 hours	20–30 years

For a drafty double-hung window, doing all the basics (rope caulk, V-strip, exterior caulk) costs $15 to $30 in materials and takes about an hour. This combination addresses the three major infiltration points.

When Window Replacement Makes More Sense

Weatherstripping and caulking are not cost-effective in these situations:

• Fogged double-pane glass — the insulating seal between the panes has failed. The glass unit must be replaced (or the full window).
• Rotted wood frames — drafts are coming through the decayed frame material itself. Weatherstripping a rotted frame is temporary at best.
• Single-pane aluminum windows — the aluminum frame is an excellent thermal conductor and will always be cold regardless of seal quality. The energy savings from replacement typically pay back within 5 to 8 years.
• Windows that won’t stay in adjustment — if a sash continually warps, won’t stay seated, or the balance system has failed, repair costs often exceed replacement.

Related Reading

• How to Seal Drafty Windows — focused guide on exterior caulking techniques
• Winterize Your Home Checklist — full seasonal prep beyond windows
• How to Fix a Sticking Window — if weatherstripping makes the window hard to open
• How to Fix Condensation on Windows — addressing moisture alongside drafts