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Windows Resources

How To Caulk Windows

According to the U.S. Department of Energy, reducing the amount of air leakage in your home is a cost-effective way to decrease heating and cooling costs, improve durability, increase comfort, and create a healthier indoor environment. To prevent air leakage, homeowners can use caulk to seal, or reseal, their windows from the outside elements. Caulk is an affordable, flexible substance used to repair cracks and gaps less than 1-quarter-inch wide. This easy DIY task can save homeowners up to 14 percent on home heating and cooling costs, according to General Electric.

While caulking can be applied to interior and exterior of windows, it’s important to understand which window areas benefit most from this home improvement— and what areas should be avoided.

Table of Contents

How To Detect Leaks In Your Windows

Window leaks can occur when window seals are broken, or pulled away, due to aging or long-term weather exposure. Leaks allow air inside your home to escape. Drafts and rain can also seep into your home through the cracks.

There are multiple ways to detect leaks around your windows:

  • On the outside of your home, check the area where two different materials meet. This includes your window corners and frame.
  • Look for cracks in the window panes.
  • Examine the existing caulking and weather stripping. Make sure both are in good condition— leaving no gaps or cracks.
  • Give your windows a little shake. If they rattle, it is a sign that the frames are not secure and air is likely leaking.
  • If you can see daylight around a window frame, there is a leak.
  • Shut a window on a dollar bill. If you can effortlessly pull the dollar bill from under the window, the window is not airtight.

Types of Window Caulk

For one window, homeowners will likely use a half-cartridge of caulk. The U.S. Department of Energy shares the most common caulking compounds on their website, which vary in strength, properties, and price.

Applying Caulk to Cracks and Leaks

Once you’ve selected the best caulk for your home, follow these best practices:

  • Clean the areas to be caulked, and remove old paint or caulk. A putty knife, screwdriver, or even a rough brush can be used to help clean the area.
  • To avoid sealing in moisture, make sure the area is dry. It is best to apply caulk during dry weather with low humidity.
  • Apply caulk to all joints in the window frame, and the joint where the frame and wall meet.
  • Hold the gun or product at a 45-degree angle, and caulk in one continuous stream.
  • Make sure the caulk sticks to both sides of a crack.
  • If caulk comes out of a crack, use a putty knife or screwdriver to push it back in.

Special Concerns for Replacement Windows

Replacement windows are typically well-sealed, so interior caulking is often optional. Instead, homeowners should pay attention to sealant is around the frame, where the window fits into the wall opening.

Windows typically come in standard sizes, but when replacing a window, the wall is often altered for the new model. Sealing those gaps is vital to your home’s comfort and energy consumption. Talk to your window replacement contractor about any questions or concerns you may have.

Be Careful With Caulk

While it may be tempting to seal any and all gaps around your windows, windows require some ventilation to prevent excess moisture from accumulating.

Avoid caulking:

  • The window’s weep hole: This small hole at the bottom of the exterior frame in windows allows moisture behind the window to exit through the frame. If you plug this hole, you could cause mold or rot to grow unchecked.
  • Moveable parts: Caulking moving parts could seal your windows closed. Avoid affecting operable parts, like sashes in a double hung window.
  • Trimmed out windows that sit above the siding: This style is common in many modern homes, where the cladding is carried out to the edge of the window frame. For this design, it is not necessary to seal the joints. Doing so will harm your windows since trimming helps carry excess moisture away from your siding and windows.
  • Above the window frame: This is a spot to avoid, no matter what kind of window you have installed. This spot is known as a drip edge, and it helps usher rain and snow away from the windows and siding. Closing off this joint can cause moisture to become trapped behind the frame and the edge of the siding.


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