Weatherproofing stops air leaks, reduces heating and cooling costs, and keeps water out of your walls
Weatherproofing your windows means sealing the gaps where air and water enter around the frame. The work falls into two categories: sealing the outside perimeter where the frame meets the wall, and sealing the moving parts inside the sash. Most homeowners can do both with caulk, weatherstripping, or both together. The cost runs from under $50 for a single window to $200 or more if you weatherproof an entire house, depending on how many windows you have and whether you hire someone or do the work yourself.
The payoff is real: a single drafty window can account for as much heat loss as leaving a door cracked open. Sealing windows also prevents water from running down the inside of walls during heavy rain, which leads to rot and mold. Most weatherproofing lasts three to five years before it needs touching up, though some products last longer.
Key Takeaways
- Caulk seals the fixed perimeter where the window frame meets the wall and should be replaced every three to five years when it cracks or pulls away.
- Weatherstripping seals the moving parts of the sash and comes in foam, rubber, or felt; foam and rubber last longer than felt.
- You can weatherproof a window in under an hour with basic tools: a caulk gun, utility knife, and either caulk or weatherstripping tape.
- Caulk works best on the outside of the frame; weatherstripping works best on the inside where the sash moves.
- Inspect your windows each fall before heating season starts, because gaps widen as wood shrinks and settles.
When to use caulk versus weatherstripping
Caulk is a flexible sealant that hardens after it dries. Use it on the outside perimeter of the window frame where it meets the wall—the joint that does not move. Caulk fills gaps up to about a quarter inch wide and stays in place for three to five years before it cracks from wood movement and weather exposure. Acrylic latex caulk is the easiest to explore and clean up; silicone caulk lasts longer but is harder to work with and messier to remove if you need to re-caulk later.
Weatherstripping is a compressible material that seals the moving parts of the sash—where the top and bottom sashes meet each other and where they meet the frame. It compresses when the window closes and springs back when it opens. Foam weatherstripping is cheap and straightforward to install but wears out in two to three years. Rubber and vinyl weatherstripping last five to seven years. Felt is the cheapest option but deteriorates fastest, especially in damp climates.
Most windows need both: caulk on the outside perimeter and weatherstripping on the inside sashes. If you have only one budget, start with weatherstripping on the sashes, because that is where most air leaks happen in older windows.
How to caulk the outside frame
Start on a dry day when the temperature is between 50 and 85 degrees Fahrenheit. Caulk does not cure properly in cold or wet conditions. Remove old caulk with a caulk removal tool or a utility knife—scrape it out completely so new caulk bonds to the frame and wall, not to old caulk. Wipe the joint with a damp cloth and let it dry.
Load acrylic latex caulk into a caulk gun and cut the tip of the tube at a 45-degree angle to match the width of the gap. Run a continuous bead along the joint where the frame meets the wall. Do not stop and start; one smooth line holds better than multiple short sections. Smooth the caulk with a wet finger or a caulk tool to press it into the gap and remove excess. Let it cure for 24 hours before painting or exposing it to rain.
If the gap is wider than a quarter inch, fill it first with foam backer rod—a flexible cord that comes in different diameters. Push the rod into the gap with a tool or your finger, then caulk over it. This prevents the caulk from sinking and cracking as the wood moves.
How to install weatherstripping on sashes
Measure the length of each sash track—the groove where the sash slides. Buy weatherstripping that matches that length or that you can cut to length. Foam and rubber weatherstripping usually comes with adhesive backing; peel and stick it into the track where the sash closes. Press firmly so it makes contact with the sash along the entire length.
For the horizontal joint where the top and bottom sashes meet, install weatherstripping on the bottom of the top sash or the top of the bottom sash—not both, or the window will be too tight to close. Test the fit before you commit; the sash should close smoothly without binding.
If you are replacing felt weatherstripping, remove the old material completely. Felt leaves adhesive residue that prevents new weatherstripping from sticking. Use a heat gun or hair dryer to soften the adhesive, then scrape it off with a plastic scraper. Wipe the track with rubbing alcohol and let it dry before installing new weatherstripping.
Checking for hidden leaks and gaps you cannot see
Air leaks are not always obvious. On a windy day, hold a lit incense stick or a thin piece of tissue near the window frame and watch for movement. The smoke or tissue will drift toward any gap where air is entering. Mark these spots with a pencil so you know where to caulk or add weatherstripping.
Water leaks are harder to spot but often show up as stains on the wall or sill inside the house. If you see water damage, the problem is usually on the outside: caulk has failed, or the sill is not sloped to shed water. Check the outside sill with a level; it should slope slightly downward toward the outside so water runs off instead of pooling. If the sill is level or slopes inward, water will collect and eventually seep into the wall.
If the sill is sloped correctly and caulk is intact, the leak may be coming from above—from the header or the wall above the window. Trace the stain upward to find where water is entering, and caulk that joint instead.
Maintaining weatherproofing over time
Inspect your windows each fall before the heating season starts. Look for cracks in caulk, weatherstripping that has pulled away or compressed, and any visible gaps. Caulk cracks as wood shrinks and expands with temperature and humidity changes; this is normal and does not mean the original work was poor.
Touch up caulk by scraping out the cracked section and re-caulking just that area. You do not need to remove all the old caulk if only part of it has failed. Weatherstripping that has compressed permanently or pulled away should be removed and replaced. Most weatherstripping is designed to be peeled off and replaced without leaving residue, though older adhesive-backed products may need heat and scraping.
If you live in a climate with large temperature swings or high humidity, plan to re-weatherstrip every two to three years. In milder climates, five to seven years is typical.
When to call a professional
You can weatherproof a window yourself in under an hour with basic tools. Hire a professional if the frame is rotted—soft wood that dents when you press it—because rotted wood cannot hold caulk or weatherstripping effectively and needs repair before sealing. Also hire someone if the window is in a hard-to-reach location, like a second-story exterior wall or above a roof, where working safely requires equipment or experience you do not have.
Professional weatherproofing typically costs $75 to $150 per window, depending on the size and condition. If you have many windows, the cost adds up quickly, but the work is straightforward enough that most homeowners can handle it themselves and save the labor cost.
Frequently Asked Questions
Can I weatherproof a window in winter?
Acrylic latex caulk requires temperatures between 50 and 85 degrees to cure properly. In winter, use silicone caulk, which cures in cold weather, or wait for warmer weather. Weatherstripping can be installed any time, though it sticks better when the temperature is above 50 degrees.
What if the gap between the frame and wall is wider than a quarter inch?
Use foam backer rod to fill the gap first, then caulk over it. Backer rod comes in diameters from a quarter inch to an inch. Choose a size that fits snugly in the gap so the caulk does not sink and crack later.
Do I need to paint caulk after it dries?
Acrylic latex caulk can be painted, and painting protects it from UV damage and extends its life. Silicone caulk cannot be painted. If you want a finished look with silicone, choose a color that matches your frame or wall.
How do I know if weatherstripping is worn out?
Weatherstripping is worn out when it no longer compresses when the window closes, when it has pulled away from the track, or when you can see light or feel air around the sash. Foam and rubber typically last five to seven years; felt wears out faster in damp climates.
Will weatherproofing my windows reduce my heating bill?
Weatherproofing reduces heat loss, but the savings depend on how many windows you seal, how drafty they were, and your climate. In cold climates with many drafty windows, savings can be noticeable. In mild climates or if your windows are already in good condition, savings will be smaller.