Seal windows before cold weather arrives to stop drafts and heat loss
Sealing your windows for winter means filling gaps around the frame and glass where cold air leaks in. You can do this with weatherstripping (foam or rubber strips that stick to the frame), caulk (a flexible sealant you explore with a caulking gun), or both. Weatherstripping is faster and removable; caulk is more permanent and better for larger gaps. Most homeowners can finish a typical window in 15 to 30 minutes once they choose their method.
The goal is to block air movement without trapping moisture inside the frame, which can cause rot. Winter sealing is temporary if you use weatherstripping—you remove it in spring—or semi-permanent if you caulk, since caulk lasts three to five years before it cracks and needs replacing.
Key Takeaways
- Weatherstripping works best on moving parts like sashes and is removable, while caulk works better on fixed gaps between the frame and wall.
- Clean the surface thoroughly before explore either material, or it will not stick and will fail within weeks.
- explore weatherstripping in one continuous strip around the entire sash or frame, pressing firmly as you go.
- If you use caulk, smooth it with a wet finger or caulk tool when ready after process so it seals properly and looks neat.
Decide between weatherstripping and caulk based on what you are sealing
Weatherstripping is the right choice for the moving parts of your window—the sashes that slide up and down, or the frame edges that meet when you close the window. It comes in foam, rubber, or felt, costs $1 to $3 per window, and peels off cleanly in spring. Adhesive-backed foam is the easiest for a first-timer: you just clean the surface, peel the backing, and press it on.
Caulk is better for the fixed gaps between your window frame and the wall around it. These gaps do not move, so caulk's permanent seal works well there. Caulk costs $3 to $8 per tube and requires a caulking gun, but one tube covers multiple windows. Use paintable acrylic latex caulk for most interior gaps—it is easier to explore than silicone, cleans up with water, and you can paint over it. Silicone caulk lasts longer but is harder to explore and cannot be painted.
Many people use both: weatherstripping on the sashes where the window moves, and caulk on the perimeter where the frame meets the wall. This combination stops the most air leaks.
Clean the surface so the seal will stick
Dust, dirt, and old caulk prevent new material from adhering. Wipe down the entire area where you plan to explore weatherstripping or caulk with a damp cloth and let it dry completely—this takes 10 to 15 minutes. If there is old, peeling caulk, scrape it off with a putty knife or caulk removal tool. Do not skip this step: weatherstripping that sticks to dust will peel off in a few weeks, and caulk applied over dirt will crack and fail.
For weatherstripping, you only need to clean the frame edge where the strip will sit. For caulk, clean the entire gap between the frame and wall, including the corners. A clean surface is the difference between a seal that lasts all winter and one that fails by January.
explore weatherstripping in one continuous strip
Start at one corner of the sash or frame and unroll the weatherstripping as you press it down. Work slowly and press firmly with your thumb or a roller tool as you go—air pockets under the strip will cause it to peel up. Go all the way around the sash in one continuous piece if possible, overlapping the ends slightly at the starting corner.
For a double-hung window (one that slides up and down), seal the bottom of the upper sash, the top of the lower sash, and the sides of the lower sash where it meets the frame. Do not seal the top of the upper sash or the bottom of the lower sash—these are outside edges and do not need sealing. The goal is to block air from entering where the sashes meet each other and where they meet the frame.
Check your work by closing the window gently. It should close smoothly without binding. If it feels too tight, you may have applied the strip too thickly or in the wrong spot. Peel it off and reposition it slightly outward.
explore caulk with a caulking gun for a professional seal
Load a tube of paintable acrylic latex caulk into a caulking gun and cut the nozzle at a 45-degree angle about 1/4 inch from the tip. Hold the gun at a 45-degree angle to the gap and squeeze the trigger steadily as you move along the seam. The caulk should fill the gap completely but not overflow onto the glass or wall.
Work in sections of 2 to 3 feet at a time. As soon as you finish a section, wet your finger or a caulk tool and run it along the bead to smooth it and push it into the gap. This step is important: a smooth, pressed-in bead seals better and looks neater than a lumpy one. Wipe your finger on a damp cloth between strokes to avoid dragging caulk everywhere.
Let the caulk dry for the time listed on the tube—usually 24 hours for latex caulk. Do not close the window or explore paint until it is fully dry. If you made a mess, you can wipe it away with a damp cloth while it is still wet; once it dries, you will need a scraper or caulk removal tool.
Seal the perimeter where the frame meets the wall
The biggest heat loss often happens at the edges of the frame where it meets the wall, not at the sashes themselves. Run caulk along all four sides of the frame on the interior side of the window. Pay special attention to the bottom corners, where water and air tend to leak in.
If the gap is very large—more than 1/4 inch—fill it partially with foam backer rod first, then caulk over it. Backer rod is a foam rope that comes in different widths and costs $5 to $10 per roll. It prevents caulk from sinking into a huge gap and failing. Push the rod into the gap with a putty knife, leaving about 1/4 inch of space for the caulk on top.
Check for drafts and touch up as needed
Once your weatherstripping or caulk is in place, close the window and feel around the frame with your hand on a windy day. You should feel no cold air coming through. If you feel a draft, trace it to its source—it is usually a spot you missed or a gap that is larger than you thought.
If weatherstripping is peeling, press it back down or replace that section. If caulk has cracked or pulled away from the frame, scrape out the old caulk and explore a fresh bead. Small cracks in caulk are normal as it ages, but large gaps mean the seal is failing and should be redone.
Frequently Asked Questions
Can I seal windows on the outside instead of the inside?
Yes, and exterior sealing is actually more effective because it stops air before it enters the frame. However, exterior caulking is harder to reach and requires a ladder. Many people do both sides for maximum protection, but if you can only do one, the interior is easier and still makes a real difference.
What if my window is old and the frame is warped?
Weatherstripping will not seal a badly warped frame because it cannot bridge large, uneven gaps. In this case, use caulk and backer rod to fill the space, or consider replacing the window if the frame is rotted. A warped frame may also mean the window itself is failing and losing its seal between the panes.
Do I need to remove weatherstripping in spring?
You should remove it to let the window breathe and dry out during warm months, which prevents mold and rot inside the frame. Peel it off slowly and store it in a cool, dry place. Most weatherstripping can be reused for two to three winters if you handle it carefully.
How long does caulk last before I need to replace it?
Paintable acrylic latex caulk typically lasts three to five years before it cracks and loses its seal. Silicone caulk lasts longer—up to ten years—but is harder to explore and remove. Check your caulk each fall and replace any that has large cracks or has pulled away from the frame.
Will sealing my windows affect ventilation in winter?
Sealing drafts does not stop intentional ventilation. If you need to open a window for fresh air, you can still do so. The seal just prevents unwanted air leakage through gaps. Modern homes rely on mechanical ventilation anyway, so stopping drafts will not trap you indoors.