Since basements are partially or completely underground, they often have inadequate windows. Adding more or larger windows to a basement can make it feel less cramped and provide a welcome natural light source. Installing an egress window will also allow the opening to serve as an exit in the case of an emergency.

If the basement is underground, remove the soil and cut an opening in the wall to accommodate the window. A retaining wall made of timbers can be laid in a stairstep design to provide an attractive view and allow the window to serve as a means of escape.

How to Install a Basement Window

Need more guidance on DIY basement window installation? The step-by-step guide below offers helpful insight into the process.

Installing a basement window is relatively straightforward for an experienced do-it-yourselfer. The project requires lumber the same dimension as the wall (likely 2” x 4” or 2” x 6”), insulation, sheathing, drywall, and consumables like nails and screws. This guide details a replacement window installation. If your project uses a new construction window, you’ll need a nailing flange. For this guide, we’ll assume the wall is open and the studs are on standard.

Step 1: Mark and Prepare the Location

The first step to installing a basement window is to decide where it will go. If wiring is in the way, you should have a qualified technician relocate any it, along with aby outlets, plumbing, or other obstacles. Never cut into a wall without knowing what is behind it. After the location has been inspected and approved, you can mark the window’s location on the wall.

Let’s say you’re installing a common 27” x 27” replacement window. You need to outline the rough opening on the wall and add ¼” to the dimensions to allow for adjustments. You’ll also need 3” of space to replace the stud you remove. So, if the window is 27” x 27”, you’ll need a 30 ¼” x 30 ¼” rough opening.

To construct the opening, you’ll have to remove a stud. Since the studs are on 16” centers, removing one stud results in a space between the remaining studs of 30 ½”. Although the opening is larger than you need, it will work for this application because you’ll use shims to fill in the extra ¼” space. Next, you will build the rough window opening.

Step 2: Building the Rough Opening

At this stage, you should have a 30 ½” wide by 93” high opening, assuming the ceilings are a standard 96” tall. Measuring up from the floor, mark where you want the bottom of the window to sit. In most projects, the measurement will be about 48” for a 27” x 27” window, but it can be placed anywhere more than 18” from the floor. If the window will be closer than 18” from the floor, the glazing (an industry term for the glass) must be tempered.

Next, make another mark to indicate the top of the opening, which will be 27 ¼” above the first. Both of these vertical marks are then transferred to the adjacent stud using a carpenter’s level. Construct the rough sill by cutting two 2” x 4” studs at 30 ½” long and nailing them together. Cripple studs are next, which are installed vertically between the bottom plate of the wall and the rough sill.

Next, cut three 2” x 4” cripple studs 45” long. You’ll nail one each to the remaining studs and one in the center between the studs on 16” centers. Doing so ensures the drywall has adequate support and won’t sag. The next step is to nail the rough sill across the top of all three cripple studs and measure for the jack studs. The jack studs will support the header above, so you’ll need two 2” x 4” jack studs at 27 ¼” long to nail to the adjacent studs and the rough sill.

To build the header, you’ll need 2” x 6” lumber and a small strip of ½” material such as plywood or OSB (oriented strand board). Since the rough opening is 30 ½” wide, you need two 2” x 6” boards cut to 30 ½” and a strip of ½” material 5 ½” wide by 30 ½” long. Nail all three pieces together to form the header and sit the entire unit on the jack studs. Face nailing from the side, nail the header to establish an opening of 27 ¼” x 27 ¼”.

Step 3: Installing the Window

Now you’re ready to install the window. Placing the window into the opening, you should see a small gap on all four sides. Use wooden shims to level the window on the sill and plumb it against the jack studs. Using the included mounting screws, drive four mounting screws (usually 2” long) through the window frame into the jack studs.

Checking one last time to make sure the window is square, you can test the operation of the window. If the window seems in a bind, it might be out of square or twisted within the rough opening. Correct this by double-checking your measurements and relocating the shims as needed. After confirming good operation, you can trim out the window opening.

Step 4: Finishing and Trim

At this point, you need to cover up the visible rough opening, which in most instances requires window casing and a finished sill. The first step is to install the sill, which is often made from 1” x 6” lumber but can also be cultured marble or other material.

After installing the sill, add window casing on the top and both sides, extending it below the sill if desired. Lastly, you’ll insulate and caulk the remaining gap between the window frame and the casing and apply paint and primer.

Editorial Contributors
Danny Lipford

Danny Lipford


Danny Lipford is a home improvement expert and television personality who started his remodeling business, Lipford Construction, at the age of 21 in Mobile, Alabama. He gained national recognition as the host of the nationally syndicated television show, Today's Homeowner with Danny Lipford, which started as a small cable show in Mobile. Danny's expertise in home improvement has also led him to be a contributor to popular magazines and websites and the go-to source for advice on everything related to the home. He has made over 200 national television appearances and served as the home improvement expert for CBS's The Early Show and The Weather Channel for over a decade. Danny is also the founder of 3 Echoes Content Studio,, and Checking In With Chelsea, a décor and lifestyle blog.

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