If you own an older home, chances are that your basement windows are made of steel or aluminum and are highly energy inefficient. Additionally, if you are in the process of finishing your basement, it is usually a good idea to replace old windows with new windows as part of the renovation. Whether you want to improve the energy efficiency of your home or update the look of your basement, replacing a basement window and finishing the interior of the window with drywall and a window sill is a home improvement project that can be completed by most homeowners.
To replace a basement window, start by removing the existing window with a reciprocating saw and pry bar. Next, purchase replacement windows that will fit within the existing window rough opening. Place the new windows in place and check level and plumbness. Once the window is positioned correctly, apply shims and use spray foam insulation to seal the gap between the window and the rough opening. Cut off any excess spray foam with a utility knife and caulk around the window as needed.
To install a drywall return around a basement window, start by cutting pieces of drywall for the top and sides of the window. Cut the drywall such that it contacts the window’s frame on one side and so that it is flush with the wall on the other side. Then, install corner bead and finish the drywall with joint compound. Caulk any joints between the drywall and the basement window.
To cut a window sill for a basement window out of standard lumber, select a piece of lumber that is approximately 1.5″ wider than the depth of the basement window cavity. You may need to “rip” the lumber to a suitable width using a table or circular saw. Trim the length of the sill so that it is 3″ longer than the window cavity on both sides. Next, use a router to give the window sill a rounded edge and use a jigsaw to cut the penetrations on both sides of the window sill – leaving a 3″ overhang on each side. Attach the window sill to the wall framing using construction adhesive and brad nails. Finally, caulk any gaps and paint the window sill (if desired).
This article will outline every step of the basement window replacement process from start to finish so that you can get a result that looks like THIS on the outside of your basement:
And THIS on the inside of your basement:
If you are more of a visual learner, you can watch my “How to Replace a Basement Window” Youtube videos linked at the end of this article.
Tools and Materials Needed to Replace a Basement Window
To replace a basement window, you will need the following Tools and Materials.
- Reciprocating Saw
- Pry Bar
- Spray Foam Insulation
- Utility Knife
- Corner Bead
- Drywall Joint Compound
- 1″x10″ Lumber (Window Sill)
Now that you know what tools and materials are needed to replace a basement window, we can begin the replacement process.
Purchase Replacement Window(s)
The first step in replacing basement windows is to order your replacement window(s). To do this, measure the rough opening of you concrete foundation window penetration and compare those dimensions to available replacement window dimensions. There are many different sizes and styles of windows, so spend sufficient time ensuring that the replacement window you purchase will fit within your existing window penetration.
Typically, this will mean that your window will be approximately 1” smaller than the concrete rough opening. For example, if you concrete foundation window rough opening is 25” wide by 19” tall, you will want a window that is approx. 24” wide x 18” tall. You will fill in the slight gap between the window and the rough opening with expanding spray foam insulation in the next steps.
Remove the Existing Window
The first step in replacing a basement window is to remove the existing window. Start by removing any screws or nails that are holding the window in place. Then, remove the glass panels (if possible).
Next, use a reciprocating saw to cut the top of the window frame and then try to loosen the frame from the concrete it is embedded within.
If the window is stuck, use a pry bar to carefully loosen it from the home’s foundation.
Be sure to wear gloves and protective eyewear during this step to avoid injury. After removing the existing window, clean up any dirt or debris with a vacuum.
Install the Replacement Window
At this stage of project, place the replacement windows in the windows rough opening and confirm fit.
There should be a slight gap between the the window and the rough opening – which we will fill in the next few steps.
Level the Window and Install Shims
To ensure the replacement window is level, use a carpenter’s level to check for any unevenness.
Use shims to make any necessary adjustments to the window’s level, placing them in the gap between the window and the rough opening.
Start by inserting shims at the bottom of the window, then work your way up.
Apply Spray Foam Insulation Around the Perimeter of the Window
Once the window is in place, secured with shims, and level, apply spray foam insulation around the perimeter of the window.
The spray foam will help seal any gaps and improve the energy efficiency of your home. Be sure to follow the instructions on the spray foam can and wear gloves and protective eyewear during this step. Additionally, if you window has mounting holes for screws, you can install those at this time. Pre-drill holes through the opening and into the concrete foundation using a carbide tipped masonry bit. Next, use a drill to drive Tapcon screws through the window and into the basement’s foundation wall.
After allowing for the spray foam to fully harden, you can cut off the excess shims with a utility knife.
Cut off Excess Spray Foam and Caulk Around Window
After the spray foam has dried, use a utility knife to cut off any excess foam that is sticking out.
Then, apply caulk around the exterior of the window to seal any remaining gaps. This will help prevent air and water from entering your basement.
If you have a damaged any of the concrete around your window, you can repair it with rapid setting concrete and trowel at this stage of the project.
At this point, perform any touch up painting as needed. Here is a look at the basement window before it was replaced:
And here is a look at the new basement window that was installed as part of this DIY Project:
After finishing the window replacement, it’s time to install drywall and trim around the interior of each basement window. For my basement finishing project, I used the “drywall return” method of finishing the basement windows – which requires no trim. Although there are many ways to successfully “trim out” a basement window, using drywall is both a simple and inexpensive method for giving your basement windows a finished look.
Although the process of building your own drywall return and window sill for a basement window is relatively straightforward, it helpful to see video of the process. As a result, I have linked my “How to Install Drywall Return and Window Sill on a Basement Window” YouTube video at the end of this article.
Prepare the Interior of the Basement Window for the Drywall Return Trim Process
For a drywall return finish for a basement window, the basement wall framing needs to have been framed to facilitate the installation of of a No-trim drywall return. In other words, the wall framing needs to be flush with the window cavity. See below:
For more information on Framing Basement walls, you can read my blog article linked here or watch my “How to frame basement Walls” Youtube Video linked here.
After ensuring that your window is new and after making any corrections to the basement wall framing (if required), you can begin to construct the basement window drywall return.
Cut the Drywall for the Basement Window Return to Length
At this stage of the basement window drywall return construction process, use a utility knife and a straight edge to cut your drywall to appropriate size.
Typically, I recommend that you install the top piece of drywall first – cutting it so that the back of the drywall contacts the window’s frame and the front of the drywall is flush with the basement wall.
Make any adjustments as needed and then fasten the drywall to the basement wall framing above with a few drywall screws.
After installing the top piece of drywall, I recommend that you install the side pieces of drywall. To do this, cut the side pieces of drywall to the correct height (don’t worry about length at this point) and position them in place on the sides of the widow cavity.
Ensure that the back of the drywall is contacting the window’s frame and then use a utility knife to cut the drywall so that it is flush with the basement wall. Refer to the image below.
After cutting both sides of the window drywall to the correct length, secure the drywall to the basement framing with drywall screws.
PRO TIP: If you want to secure the drywall to the concrete window cavity as well, use a carbide tipped masonry bit to pre-drill holes for the screws. Then use Tapcon screws to secure the drywall to the concrete or cinderblock basement window wall cavity.
Apply Drywall Corner Bead and Joint Compound to the Basement Window Corners
After cutting and installing the drywall around the top and sides of the basement window, it’s time to finish the drywall outside corners – just like you would for any other drywall project.
First, cut your corner bead to the appropriate length using tin snips. Next, apply drywall joint compound to the outside corners and push the corner bead into place. Use a drywall finishing knife to finish the corners of the window – similar to how you would finish outside corners of any drywall project. For more information on how to finish drywall in a basement, check out my “Basement Drywall Finishing Tips and Tricks” YouTube video linked here.
After finishing the outside corners, allow the drywall compound to dry and sand down any imperfections.
Cut the Basement Window Sill to Size
After installing drywall on the tops and sides of the window cavity and finishing the outside corners with corner bead and joint compound, it’s time to measure and cut the window sill to length.
First, measure the distance from the window frame to the face of the basement wall.
After getting that measurement, add approx. 1″ for the window sill overhang that will be on each side of the window. Select a piece of common lumber or hardwood lumber (depending on your budget) that is 1″ thick and as wide (or wider) than the measurement you made from the window frame to the face of the basement wall (+1″). Use a table saw or circular saw to “rip” the lumber (if needed) to the appropriate dimension.
After ripping the window sill board to the correct width, measure the length of the window cavity.
I recommend that you add approximately 6″ to this length – 3″ for the overhang on one side of the window and 3″ for the overhang on the other side.
Next cut the window sill to the correct length.
Use a router to give the window sill a rounded edge
After cutting the window sill to the rough dimensions needed, use a router (I recommend a 3/4″ round over bit) to give the edges of the window sill a rounded edge.
Although this step is not 100% necessary, I believe that it will help to give the window sill more of a professional, finished look
Cut the Window Sill Overhang
Finally, cut out the penetration on the window sill such that you can slide the window sill into the basement window cavity and so that there will be a 1″x3″ overhang on both sides of the window.
I recommend that you cut the penetration in the window sill with a jig saw.
After making the window sill cuts for each of your basement windows, perform a dry fit to ensure that each of the window sills fit properly. Make any adjustment at this time (if needed)
Sand Down any Rough Edges on the Window Sill
After cutting the window sill and rounding over the edges, use 120 grit sandpaper (and an orbital sander if you have one) to sand down the window sill.
Ensure that you remove any rough edges and smooth out any imperfections before proceeding.
After sanding the window sill as required, you can paint or stain the window sill at this stage (if desired).
Install the Window Sill
To install the window sill in the basement window cavity, start by applying construction adhesive to the rough in window frame lumber.
Next, take the window sill and position it in place within the window cavity. Be sure to firmly embed the bottom side of the window sill into the adhesive.
Next, use a level to check that the window sill is perfectly level in the window cavity. Check level length -wise and width-wise. After confirming that the window sill is perfectly level, use a brad nailer and 2.5″ brad nails to fasten the window sill to the wall framing below.
Caulk Around the Window and Window Sill
At this point, use caulk gun and a high quality caulk to seal any gaps between the window, drywall, and window sill. Apply caulk around the window frame where it contacts the drywall and window sill using an even bead of caulk. Additionally, don’t forget to caulk the underside of the windowsill.
After installing caulk around the window, you have successfully installed replaced a basement window, installed a drywall return, and installed a window sill.
If you are more of a visual learner, you can watch my “How to Drywall Around a Basement Window” Youtube video(s) linked below.
Thanks so much for checking out ATImprovements! If you learned something from this project, you might also like these other DIY Projects:
- How to Build a Concrete Slab Shed Foundation: https://atimprovements.com/how-to-build-a-shed-base-concrete-slab-step-by-step-diy-guide/
- How to Frame a 10’x10′ Shed Base: https://atimprovements.com/how-to-build-a-shed-floor-base-diy-step-by-step-guide/
- How to Frame Shed Walls:https://atimprovements.com/how-to-frame-a-shed-how-to-frame-walls-for-a-10×10-modern-shed-step-by-step-with-pictures/
- How in Install a Shed Window: https://atimprovements.com/shed-window-installation-how-to-install-a-window-in-a-shed-diy/
- How to Install a Roll Up Door in a Shed or Garage:https://atimprovements.com/roll-up-door-installation/
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