How to Frame a Window Opening in an Existing Wall

Windows offer your home natural sunlight, a view outside, and energy efficiency. Because windows provide so much to your home, you may decide to add more of them. With the right materials and preparation, framing a window opening is something you can tackle on a weekend afternoon.

There are several different types of replacement window frames to choose from, each serving a unique purpose. Be sure to carefully consider your options before installing new frames. Common weather, energy efficiency, and aesthetics are all factors that will influence your choice of which option makes the best window frame for your home. 

Keep in mind that you may need framing members that are larger than 2x6, depending on how wide your window is. Consult with a window contractor or specialists at your home improvement store for appropriate sizes.

Prepping to Frame a Window

The best time of the year to frame a window opening is during the spring or summer seasons, when the weather is the most accommodating. You’ll have an open space through your wall until the project is complete, so frame your window opening when the forecast is warm and clear to prevent your home’s exterior from being vulnerable to harsh weather conditions.

Once you’ve gathered your tools and supplies, follow these steps for framing a window opening:

Mistakes to Avoid

When framing a window, you’ll want to avoid these common mistakes so your window doesn’t experience any.

1. Incorrect Measurements

If you don’t have the right measurements, the window frame and rough opening won’t match—this could cause drafts, leaks, and other problems. Choose standard-size windows to avoid this problem, or have a family member or friend double-check measurements for you for accuracy.

2. Poorly Affixing Your Weather-Resistant Barrier

If your weather-resistant barrier and flashing are poorly adhered to, your window’s sealing will be compromised, leading to issues with insulation. This could create drafty homes in winter and hot homes in summer—and lead to higher energy bills. When affixing your weather-resistant barrier, make sure the window sill is clean and free from dust and debris. You should also install your windows on a day with excellent weather—rainy days, cold days, or humid days could affect the adhesive’s ability to stick.

3. Forgetting to Check Window Placement

Your window must be centered, level, and plumb—otherwise, you’ll find yourself dealing with gaps (which can cause insulation issues as described above) and structural problems. When you install the window, use a level to confirm it is straight and centered within the rough opening. 

4. Neglecting the Back Slope

The sill on your rough opening must be sloped so it can send water away from the building. Make sure you cut the cripple studs at an angle or add a sill-wedge or sloped pan after the rough opening has been framed.

DIY vs. Hiring a Pro

When framing a window, you will be staring through a rather large hole in your house until you complete the project. That’s why you’ll need to make sure you have the time, tools, and supplies to do the work. 

But you don’t want to rush, either. Mistakes in window framing can leave the window—and your home—susceptible to moisture and drafts. If a window is framed incorrectly, it can affect the integrity of the window because the frame is what’s keeping it in place. Additionally, if you’re replacing a window frame that has rotted, whether in part or fully, you’ll be adding to the time and complexity of your project by repairing the wall and removing the wood. 

All told, you may want to save your DIY skills for another project and consider hiring a pro to reframe the window for you instead. Replacing a window frame will cost $200 to $600, depending on the materials used. Keep in mind that labor costs will raise the price because the pro will have more prep work to do.