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How To Caulk Windows (2024 Guide)

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Author Image Written by Jessica Wimmer Updated 06/05/2024

Leaky windows can be more than just a nuisance. A drafty house comes with increased energy bills as your HVAC system struggles to keep the indoor temperature consistent. Fortunately, with a little caulk, you can often seal leaks around a window’s frame yourself.

In this article, we’ll provide a step-by-step guide on how to caulk windows, share the tools you’ll need for this project, and offer expert caulking tips. We’ll also help you determine whether you need to replace your windows for a more comprehensive solution to leaks and skyrocketing utility bills.

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In this video, Ask This Old House home technology expert Ross Trethewey and master carpenter Nathan Gilbert share some tips on sealing and insulating existing windows.


Why Do You Caulk Windows?

Caulking a window gives it a more finished appearance while also sealing any air leaks or drafts. It also improves the window’s insulating properties and protects your home’s energy efficiency. You’ll know it’s time to use caulk when you detect a leak around your window. 

If the leak is bad enough, you may spot water damage or fogged glass from rain. However, smaller air leaks may require some detective work. Here’s what to do if you suspect a window is leaking:

  1. Close and lock all of your windows to get the tightest seal possible.
  2. Turn off all fans, air conditioners, furnaces, and any other appliances that circulate air.
  3. Create a small stream of smoke with a lit candle or an incense stick.
  4. Move the candle or incense around the window’s frame, carefully avoiding any drapes or window treatments.
  5. There’s a leak everywhere the flame flickers or the smoke blows away from the window.
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Window Replacement

Window replacement typically costs $300–$2,000 per window, depending on the window type.

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Window Repair

Window repair typically costs $177–$623, but it can vary based on the type of repair.

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Window Cleaning Cost

Window cleaning typically costs $80–$430 for an entire home.

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How To Prep for Caulking Windows

Make sure you have the right weather conditions and tools for the job before beginning to caulk. Be aware that you’ll need to remove the old caulk before you can apply a new layer.

Picking the Right Day to Caulk

Wait for a day with mild weather and low humidity, especially if you’re caulking your windows’ exteriors. The weather should be at least 45℉, and the forecast should be free from rain for at least 24 hours. This allows time for the caulk to dry and set properly.

Tools Needed for Caulking

You’ll need the actual caulk plus the following tools and supplies:

  • Caulking gun
  • Caulk-smoothing tool
  • Cleaning rag
  • Foam backer rod (for larger cracks)
  • Painter’s tape (optional)
  • Putty knife
  • Small nail or pin
  • Utility knife

Steps to follow
Here are some step-by-step instructions for mess-free window caulking on all different types of windows.

Trying to apply new caulk over old won’t create a durable seal, so start by scraping off the old caulk with a putty knife. You may also need a utility knife to cut out stubborn caulk fragments. Make sure to remove as much as possible.

Scrape or wash away dirt or other debris from the area where you intend to apply caulk. If you skip this step, the caulk may not adhere well to the window. Repair any rot or damage to the window frame first. Also, remember that caulk works best as a sealant for gaps of 1/4 inch or less. 

Fill any larger cracks with a foam backer rod before applying caulk. You can also apply a border of painter’s tape parallel to the cracks about 1/8-inch away so that you’ll get a straighter line and have an easier time with cleanup.

Caulk tubes are often sold separately from the gun used to apply it. It’s easiest to choose a manual caulking gun with a smooth rod rather than a ratchet rod. Smooth rod guns are a little less common and more expensive, but you won’t have to use as much force to apply the caulk. Additionally, these guns have a thumb release that stops the caulk from flowing immediately, preventing pooling and creating a neater end result.

Whichever type you choose, load the tube into the gun as instructed. Make sure the rod is fully extended and the plunger cup rests securely against the back of the tube.

Tubes of caulk come sealed, so you must cut an opening for the caulk to flow through. The wider the opening, the larger the bead of caulk that will come out, so take care when making this cut. Use the utility knife to cut off the last 1/4-inch of the nozzle’s tip at a 45-degree angle. You might also need to insert a small nail or pin to break the seal on the inside of the nozzle.

Starting at the corner of the window, press the nozzle tip firmly against the surface. While holding the gun at a 45-degree angle, apply pressure to the trigger and drag the nozzle steadily along the crack or joint, creating a smooth, continuous bead of caulk in the gap. When possible, slide the nozzle along the smooth window edge rather than any siding or textured walls. If this is your first time using a caulk gun, you may want to run a test bead on a sheet of scrap paper to get a feel for it first.

Use both hands on the gun, with your dominant hand on the trigger and the other supporting the barrel near the nozzle. Keep your wrists straight and move your elbows or upper body as you go to create the smoothest line. Although you can caulk the window edge from corner to corner, you’ll often get a neater line if you caulk from each corner to the center, joining the beads in the middle.

After applying each line of caulk, take your caulk-smoothing tool and drag the tip lightly over the bead, which will remove excess caulk and ensure it fills the entirety of the gap. You can also use a popsicle stick or even your finger covered with a wet rag. If you used painter’s tape, remove it after you’ve smoothed the caulk but before it has time to set. Wipe away any remaining excess caulk with a clean, damp rag.

A skin will form over the fresh caulk within a few hours, but most caulk needs about 24 hours to fully set. Check the manufacturer’s instructions on the caulk tube to see if it needs any longer. These instructions should also tell you when you can safely paint over the dried caulk.


Areas To Avoid When Caulking Windows

We’ve covered the parts of your windows where you need to apply caulk, but since many homeowners use caulk where it isn’t needed, here are some areas to avoid:

  • Weep holes: Some windows have small weep holes along the bottom exterior frame to allow moisture and condensation to drain out. If you seal them, mold may grow, or the wood could rot.
  • Trimmed-out windows: Some windows have extra exterior trim that sits atop the siding to make them appear larger. You don’t need to apply caulk around the outside of these frames, as it won’t offer any extra protection and may end up sealing moisture in instead of out.
  • Movable parts: Keep caulk away from sashes, casements, and other moving parts, or you could seal your windows shut. These areas often have rubber gaskets to prevent leaks. Replace the gaskets instead of using caulk if leaks develop.
  • Above the window frame: The ledge above the window frame should already have a drip edge to direct precipitation away from the window. Applying caulk could prevent it from doing this job.

Types of Window Caulk

A few different types of caulk are used around windows. The right caulk for your project depends on where you need to apply it. Caulk for the exterior of a house must be more durable to stand up to water and weather. Different types of caulk also adhere better to different surfaces. If you plan to caulk both exterior and interior windows, you’ll need two different types.

Polyurethane caulk is a great choice for sealing exterior window surfaces because it’s high quality and can adhere to wood, glass, metal, and other materials. However, it’s more expensive than other varieties and can break down in sunlight over time unless it’s coated with UV-resistant exterior paint.
Another highly durable exterior caulk, silicone caulk is extremely water resistant. Unfortunately, it doesn’t adhere well to wood, and paint won’t stick to it, so it may remain visible on your window trim.
Siliconized latex caulk is well-suited to most interior projects because it adheres to many types of surfaces and holds up to varying temperatures and moisture conditions. It’s also paintable, though it shouldn’t be used outdoors because it can’t stand up to extreme weather.
Acrylic latex caulk is not a good choice for leaky windows. It will quickly break down because it can’t expand and contract with changing temperatures. This caulk is better used for securing things like baseboards.

DIY vs. Professional Window Caulking

Most homeowners can caulk windows with little more than a trip to the hardware store. However, you may want to consider calling a professional window contractor for windows that are difficult to access or located above the ground floor. A professional will have the right experience and safety equipment to do the job quickly and neatly. Call a professional if your windows need more than simple caulk and account for labor in your window repair budget.


Caulking Windows vs. Replacing Windows

If your windows are relatively new and still in good condition, some caulk might be all you need to plug up air leaks. Caulking is an easy do-it-yourself (DIY) job that can improve your home’s energy efficiency, and it’s far less expensive than even the most affordable window replacement options. Applying weatherstripping to sashes and solar control films to window panes can also improve efficiency. However, these methods have their limits, particularly if your windows are uninsulated or in poor condition.

This Old House Tip
You should consider replacing your windows with more energy-efficient alternatives if you want to maximize your energy bill savings. Top window brands offer highly insulated double- and triple-pane windows that contain treated glass to raise efficiency and reduce heat transfer.

If you think you need to replace your windows, consider installing energy-efficient windows. These replacement windows typically cost $320–$2,000 for materials plus installation. There are a few situations in which it may be better to upgrade to a high-quality window replacement than use caulk, including the following:

  • Your windows are more than 20 years old
  • You have single-pane windows
  • You have aluminum or uninsulated vinyl frames
  • The window frames are rotten or water damaged

*Cost data in this section is sourced from contractor estimates used by Angi.


Our Conclusion

Applying caulk can often fix small leaks around a window frame. You can typically do this yourself with a few simple materials and tools. Sometimes this will solve the problem, but it may be time for an upgrade if your windows are old and inefficient. The Department of Energy estimates that 25%–30% of home heat loss happens through leaky windows, so you may save money on your energy bills by caulking or replacing your windows.

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FAQ About Caulking Windows

Do you caulk the outside or inside of windows?

You can caulk both the outside and inside of windows, but you’ll need different types of caulk for each.

Should I caulk or replace a window?

Caulk can seal small air leaks in windows that are in otherwise good condition, and replacing old caulk can help improve your home’s energy efficiency. However, replacement may be the better option for old, inefficient windows or windows that are in poor condition.

What happens if you don't caulk your windows?

If you don’t caulk your windows, treated air may leak out of your home or drafts may leak in. This causes your air conditioner or furnace to work harder, leading to increased energy bills.

Where should you not use caulking?

You should not use caulking on weep holes, trimmed-out windows, moving parts, or the ledge above the window frame. If your windows are extensively damaged, consult a professional to see if caulking will be enough or if it’s time for a bigger repair or replacement.

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