How to Inspect Window Seals and Caulking
Walk around your home and visually inspect the caulk and weatherstripping on every window. Run your hand or an incense stick along the edges to feel for drafts, recaulk any cracked or missing sections with exterior-grade sealant, and replace weatherstripping that is compressed or torn.
- Time
- 20 min
- Frequency
- twice a year (spring and fall)
- Difficulty
- easy
- Cost
- $5
What you'll need
- Incense stick or candle
- Caulk gun
- Utility knife
- Damp cloth
The steps
- 1
Start with a visual inspection of each window
Look at the caulk line where each window frame meets the siding or trim, both inside and outside. You are looking for cracks, gaps, missing sections, or caulk that has pulled away from the surface. Discolored or chalky caulk has lost its flexibility and will fail soon even if it looks intact.
- 2
Check for drafts with your hand or incense
Hold your hand or a lit incense stick near the edges of each window. Move slowly along the top, bottom, and both sides. A draft will deflect the smoke or feel cool on your skin. Do this on a windy day for the most obvious results. Mark any spots where you detect air movement.
- 3
Inspect the weatherstripping
Open each window and examine the weatherstripping in the channel and along the sash. Press it with your finger. Good weatherstripping springs back. If it stays compressed, is torn, or is missing entirely, it needs replacement. Foam weatherstripping degrades fastest and usually lasts only one to two years.
- 4
Note cracked or missing caulk
Use a notepad or your phone to record which windows need attention and whether the issue is interior caulk, exterior caulk, or weatherstripping. This saves you from making multiple trips to the hardware store.
- 5
Recaulk gaps and cracks
Score and peel out the failed caulk with a utility knife. Wipe the surface clean with a damp cloth and let it dry. Apply a steady bead of DAP Dynaflex 230 or similar exterior-grade sealant along the gap. Smooth with a wet finger. Work when the temperature is above 40°F for proper adhesion.
- 6
Check that weep holes are clear
Most windows have small weep holes at the bottom of the exterior frame. These drain condensation that collects inside the frame. Poke a toothpick or thin wire into each hole to clear any debris. Blocked weep holes cause water to pool inside the frame and rot the sill.
Why window seals matter
Failed window seals cost you money every month. Even a small gap in caulk or a compressed piece of weatherstripping lets conditioned air escape and outside air in. The Department of Energy estimates that air leaks around windows and doors account for 25 to 30 percent of heating and cooling energy use in a typical home.
Beyond energy costs, failed seals let moisture in. Water that gets behind siding or into a window frame causes rot, mold, and paint failure. A $5 tube of caulk now prevents a $500 sill repair later. This is one of the highest-return maintenance tasks you can do.
How to spot failing seals
Three things tell you a seal is failing: what you see, what you feel, and what you hear.
Visual signs. Caulk that is cracked, peeling, or pulling away from the surface has lost adhesion. Discolored or chalky caulk has broken down from UV exposure. Look at the interior side too. Water stains on the sill or drywall below a window mean water is getting past the seal.
Draft signs. On a cold or windy day, hold your palm near the window edges. Moving air means a gap exists somewhere. For a more precise test, light an incense stick and move it slowly around the window perimeter. The smoke will deflect visibly toward even small leaks.
Sound signs. If you hear wind whistling near a window during storms, the seal or weatherstripping has a gap large enough to channel airflow. This usually means the weatherstripping has failed, not just the caulk.
The incense draft test
The incense test is the most reliable DIY method for finding air leaks. Light the incense and hold it about an inch from the window edge. Move it slowly along all four sides. Where smoke gets sucked toward the window or blown away from it, mark the spot with a small piece of tape.
Do this test on a windy day or when there is a temperature difference between inside and outside. You can also run a box fan in a nearby window blowing outward to create a slight negative pressure inside the room, which pulls outside air in through any gaps and makes them easier to detect.
Test every window in the house in one session. It takes about two minutes per window and saves you from discovering a missed leak in January.
When to recaulk vs replace weatherstripping
Caulk seals the gap between the window frame and the wall. Weatherstripping seals the gap between the moving sash and the fixed frame. They are different materials that solve different problems.
Recaulk when you see cracked, missing, or separated caulk along the exterior or interior trim. Remove the old caulk completely before applying new. Caulking over failed caulk does not stick and peels off within a season.
Replace weatherstripping when the draft is coming from the operable part of the window, the part that slides or swings. If you can rattle the sash when the window is closed, the weatherstripping has compressed too much to seal. V-seal (V-strip) weatherstripping lasts the longest for most window types and is easy to install yourself.
If both are failing on the same window, do the weatherstripping first. Replacing it requires opening the window, which can crack fresh caulk if you do it in the wrong order.
Frequently asked questions
- How do I know if a window seal has failed?
- Fog or condensation between the panes of a double-pane window means the seal has failed and the insulating gas has escaped. Drafts around the frame, visible cracks in the caulk, and higher-than-expected energy bills are also signs.
- Can I use silicone caulk on window exteriors?
- You can, but silicone is not paintable. Use a siliconized latex caulk like DAP Dynaflex 230 if you plan to paint the trim. Pure silicone is better for areas that will stay unpainted and need maximum flexibility.
- How often should I inspect window seals?
- Twice a year, in spring and fall. Spring catches damage from winter freeze-thaw cycles. Fall catches summer UV degradation before heating season starts.
- Is foggy double-pane glass something I can fix myself?
- No. Fog between panes means the factory seal has failed. The glass unit needs to be replaced by a professional, but you can usually replace just the glass unit without replacing the entire window frame.
Products you'll need
This section contains affiliate links. We may earn a commission at no cost to you.
DAP Dynaflex 230 Sealant
Flexible exterior window and door caulk
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