How to Caulk Windows for Winter (Step-by-Step Guide)
Drafty windows? Here is how to caulk windows for winter in one afternoon: scrape old caulk, prep the joint, and apply $15 in exterior caulk for a 5-10 year seal.
Caulk is one of those maintenance tasks that most houses need every five to ten years and most homeowners skip until they actually feel a cold draft. Windows are the main place it fails: the bead between the frame and the siding or trim shrinks, cracks, and pulls away, and by the time there is a noticeable draft in January the gap has been there since spring.
Knowing how to caulk windows for winter takes one afternoon and about $15 in materials. The Department of Energy notes that caulking and weatherstripping can reduce heating and cooling bills by up to 15 percent, and windows are where that savings is easiest to capture.
Quick answer: Scrape old caulk from the exterior joint where the window frame meets the siding or trim, clean and dry the surface, and run a bead of siliconized acrylic exterior caulk in a single smooth pass. Smooth with a wet finger. The whole job takes two to three hours for a typical house, costs $15-30 in materials, and stops most window drafts for 5-10 years.
How to Tell If Your Windows Need Caulking for Winter
Before buying anything, check whether caulk is actually the problem. On a cold or windy day, hold your hand flat near the outer edges of each window frame, where the frame meets the trim or siding. Any air movement means a gap.
A lit incense stick gives a more sensitive read. Hold it near the joint and watch the smoke. Even a slow leak shows as the smoke drifting sideways instead of rising straight.
Most drafts come from the exterior joint, not the glass. The bead where the window’s brick mold or casing meets the exterior siding is the one that weathers and fails. Interior leaks at the trim-to-drywall joint are worth sealing too, but that is a separate pass done from inside and usually with a thinner bead.
What You’ll Need
- Caulk gun (a basic $12 model works fine)
- Siliconized acrylic exterior caulk, paintable, in white or a color matching your trim
- Utility knife
- 5-in-1 tool or putty knife
- Stiff-bristle brush
- Painter’s tape (optional, but makes cleanup faster)
- Damp sponge or cloth
- Small bucket of water
- Ladder for second-floor windows
Step 1: Remove the Old Caulk
If the existing bead is still bonded and only has a hairline crack down the center, a fresh bead applied over it can work. When it is peeling, shrinking, or pulling away from one side of the joint, scrape it out first. Layering new caulk over a loose bead gives you the same result in half the time.
Work a utility knife along both edges to free the bond, then peel the old bead out with a 5-in-1 or putty knife. Older caulk that has been in place 10-plus years often crumbles rather than peels. A caulk softener spray, around $5 at any hardware store, soaked for 20 minutes makes it pull out in strips instead.
Once the joint is clear, brush out any loose debris with a stiff-bristle brush.
Step 2: Clean and Dry the Surface
Wipe the joint down with a damp cloth and let it dry completely. Caulk will not bond to a dusty or wet surface. If there is any paint peeling from the trim near the joint, scrape it back before caulking. Caulk applied over loose paint pulls away with the paint.
Temperature matters here. Most exterior caulks need to be applied at 40°F or above to cure properly. A mild fall afternoon in the 50s or 60s is ideal. Below 40, the caulk gets thick, will not spread evenly, and often does not cure all the way through.
Step 3: Choose the Right Caulk
For exterior windows, siliconized acrylic is the standard choice. It bonds to wood, vinyl, and painted surfaces, stays flexible through freeze-thaw cycles, and accepts paint once cured. DAP Alex Plus and GE Supreme are both commonly available, priced in the $6-9 range per tube, and rated for 10-plus years under normal conditions.
If the joint involves metal window frames or bare glass rather than wood or painted trim, 100% silicone is more durable. The drawback is that it will not take paint, so it only works where you do not plan to repaint over it.
Skip regular latex “painter’s caulk” for exterior joints. It dries brittle and starts cracking within a season or two when exposed to temperature swings.
A standard 10.1-oz tube covers roughly 15-20 linear feet at a 1/4-inch bead width. A house with 10 to 15 windows typically goes through 3-5 tubes. Buy one extra to have on hand.
Step 4: Apply the Caulk
Cut the nozzle at a 45-degree angle, about 1/4 inch back from the tip. Run painter’s tape along both sides of the joint if you want clean lines. It adds five minutes but the cleanup afterward goes much faster.
Hold the gun at about 45 degrees and pull it steadily along the joint in one pass, moving from one corner of the window to the next. The goal is to fill the gap, not just skim the surface. For gaps wider than 3/8 inch, push the nozzle tip slightly into the gap as you move. Very large gaps, over 1/2 inch, should be packed loosely with backer rod foam first and then caulked over.
Move at a pace that keeps the bead consistently about 1/4 inch wide. Too slow and you get thick spots. Too fast and the bead strings out thin and misses gaps.
Step 5: Smooth and Finish
Dip your finger in water and run it along the bead in one smooth stroke. This tools the caulk into the joint and leaves a slightly concave surface that sheds water better than a rounded bead. Keep the damp cloth close for excess.
Work one joint at a time rather than caulking the whole window before smoothing. The caulk skins over quickly in dry weather.
If you taped, pull the tape immediately while the caulk is still wet. Pull it at a low angle, back toward the joint. Waiting until the surface starts to skin makes it tear.
Let siliconized acrylic cure for 24-48 hours before painting over it.
Common Mistakes
Using painter’s caulk on exterior joints. It is cheap and everywhere at hardware stores, but regular latex caulk does not flex with the wood. By the following fall the joint is cracked open again. Spend the extra dollar per tube for the silicone-enhanced version.
Caulking over a loose bead without removing it. Tempting to skip the scraping step, especially on a high window where you are up a ladder. New caulk over lifting old caulk fails just as fast. The scrape-and-prep step is what makes the repair last.
Sealing the window sill. The exterior sill should have a small gap at the outer edge so rainwater can drain away from the frame. Caulk the frame-to-siding joint but leave the sill’s outer edge open. Trapping moisture behind a fully sealed sill rots the wood below the sill faster than any draft would have.
Caulking when it is too cold. Below 40°F, exterior caulks thicken in the tube, will not lay smoothly, and often fail to cure completely. Wait for a warmer afternoon.
Caulking the operable sash. The parts of the window that open need weatherstripping, not caulk. Running a bead across an operable sash seals it shut for the winter. Caulk only the fixed exterior joints.
When to Call a Pro
Window caulking is about as low-risk as home repair gets. The one scenario where it becomes a different job: if you scrape out old caulk and find soft, punky wood in the frame or sill underneath. Caulking over rotted wood traps moisture and accelerates the decay rather than stopping it. A carpenter needs to cut out the damaged section, treat and dry the area, and replace the wood before the joint gets recaulked.
Large gaps over 1/2 inch wide, or windows that have shifted visibly in their openings, can point to foundation movement or settlement rather than simple weathering. Worth a second opinion before sealing.
FAQ
What type of caulk should I use for exterior windows? Siliconized acrylic, sometimes labeled “silicone-enhanced acrylic” or “elastomeric acrylic,” is the standard choice for wood and vinyl window frames. It bonds well, stays flexible through temperature swings, and accepts paint once cured. DAP Alex Plus, GE Supreme, and Loctite PL Window and Door are all solid options in the $6-9 range.
How often should I recaulk windows? Most exterior caulks hold for 5-10 years under normal conditions. South-facing windows see more UV and thermal cycling and tend to fail sooner. A quick visual check each fall, looking for gaps, shrinkage, or cracking in the bead, catches failures before they become noticeable drafts. DAP rates several of their exterior caulks for 10-plus years.
Can I caulk windows from the inside? Interior caulking at the trim-to-drywall joint is worth doing in older homes and adds to the overall air seal. But the primary joint to seal is the exterior one, where the frame meets the siding or brick mold. Interior-only caulking does not stop cold air that is entering through an open exterior gap.
Do I need to remove old caulk before applying new? Only if the old bead is lifting or pulling away from the joint. A bead that is still bonded but has a hairline crack down the center can usually be caulked over. When in doubt, check by pressing the old bead with your finger. If it flexes and stays bonded, you can go over it. If it moves or lifts, scrape it out.
What is the difference between caulk and weatherstripping on windows? Caulk seals the fixed exterior joints where the window frame meets the trim or siding. Weatherstripping seals the movable parts, where the sash meets the frame when the window is closed. A well-sealed window needs both. See our guide on weatherstripping windows for the interior part of this job.
Can I caulk windows in winter? Interior joints can be caulked any time of year. Exterior caulking requires temperatures above 40°F for proper curing. If it is already too cold, removable rope caulk, pressed into the gap from the inside, is a temporary fix that peels off in the spring.
How much caulk do I need? A standard 10.1-oz tube covers roughly 15-20 linear feet of 1/4-inch bead. For a typical double-hung window with four sides to seal, figure about 15-18 linear feet per window. A 10-window house usually takes 3-5 tubes. Pick up one extra so you have it on hand for touch-ups.
Does caulking windows really make a difference? On a drafty house, yes, noticeably. On a newer house with tight windows, the gains are smaller. The biggest returns come from windows in older homes where the original caulk has never been replaced, or any window where you can actually feel air movement with your hand. The Department of Energy estimates air sealing and weatherization together can cut heating bills by up to 15 percent, and windows are one of the easiest places to start.
If you are doing a full fall furnace and heating prep, window caulking fits naturally into the same weekend. You can also add door sweeps and weatherstrip your doors while you have the caulk gun out.