How to Install an Egress Window in Your Basement

Good planning simplifies the job

Mark the window outline

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Outline your proposed basement window size (frame) with masking tape on the wall to get a feel for the placement and size of your window. Add in space for the header, if you place the window perpendicular to the floor joists (like the one here).

Build a temporary support wall

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Erect a temporary 2×4 support wall if the joists are perpendicular to the wall you’ll be cutting. Place it 3 ft. back from the concrete wall. Screw the top plate to the joists and align the studs directly under the floor joists. Measure and cut each stud for a tight fit.

Hang plastic to contain dust

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Tent the area where you’ll be cutting with 6-mil plastic sheeting to confine the dust. Use sheeting at least 8 ft. 6 in. to 9 ft. wide.

Close-up: Seal the area between joists.

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Make slits in the sheeting to seal the area between the joists and staple it in place. First, find the best location and size for the basement window. Consider: (1) which wall offers the best light; (2) the effect on the exterior look of the home; and (3) the obstacles you’ll have to deal with for a particular location.

The best natural light comes from the east first and then the south. An eastern window offers rich morning light, while a southern window provides more even light year-round. We centered our egress basement window beneath a large bow window on the front of the house (facing east). This placement maintained the balanced look of the front of the home, though the window was not centered on the wall of our new basement room.

Check for obstacles such as buried utilities, shrubbery, indoor wiring and ductwork. The more stuff you have to move or work around, the more complex, time-consuming and expensive the project becomes. Always call for buried utility marking so you don’t hit or interfere with water, gas, electrical, cable or sewer lines when you dig your well. Then visit a window dealer or home center and pick up a manufacturer’s brochure listing window sizes to help plan and size your basement window.

One key factor that can limit basement window size is the size of the beam (called a header) that you have to install when you remove a section of your foundation wall. If you’re installing a small window (less than 48 in. wide) in a wall that runs parallel to the floor joists, you probably won’t need the extra support of a header. But if you install the window in a load-bearing wall (perpendicular to the floor joists; Photo 2), consult a structural engineer or architect to determine the header size.

Take a sketch of your plan (Fig. A) to your local building inspector’s office to obtain a permit for the project. Local code officials should be familiar with local issues and can help you with details. We actually finished our well first, but it’s usually easier to get the basement window in and then finish the well around it.

TIP: Keep a tarp handy so the sides of the well won’t wash in if it rains.

When you position your basement window layout with masking tape, remember to make the cutting lines about 3-1/2 in. wider than the rough opening required (listed with the window dimensions). Add the width of the header plus 1-3/4 in. to the rough opening height. The extra space is for the 1-1/2 in. treated wood rough frame (Fig. A) plus room for adjustment. Cutting through concrete isn’t as exact as cutting through wood!

Since our egress basement window was in a wall perpendicular to the floor joists (in a weight-bearing wall), we built a temporary support wall (Photo 2) to carry the weight before cutting out the window opening and putting in the header. Sawing concrete creates an incredible dust cloud. So when cutting inside, tent the area around the cut to confine the dust (Photo 3).

CAUTION!

Avoid putting an egress basement window near a walkway unless you provide a substantial barrier to prevent falls into the well.

Tip:

The simplest way to avoid the header size issue is to make an existing basement window taller. Typical small basement windows measure 30 in. wide by 15 in. high. If you extend this opening down and install a 29-in. wide by 47-in. high casement window, you’ll satisfy minimum egress window requirements.

Rent a concrete saw with a diamond blade

Drill a pilot hole

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Measure down from the joists to locate the height of the bottom cut. Mark the center of the bottom cutting line and drill a level pilot hole with a hammer drill and a bit long enough to go through the wall.

Mark the window dimensions on the exterior

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Level from the pilot hole on the exterior in both directions from the center and measure and mark the corners of the cutout. The mortar lines usually serve as a level reference line too. Drill a level hole through the wall at each corner.

Cut the concrete

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Cut a 1/2-in. deep groove in the concrete block with an electric 14-in. concrete saw equipped with a diamond blade. Then complete the cut on a second pass. Wetting the blade as it cuts reduces dust. Caution: Plug the saw into a GFCI outlet. Your basement or lower-level walls will be either poured concrete or concrete block. In this article, we show you how to cut through concrete block. For a poured concrete wall, we strongly recommend that you hire a professional to cut the opening ($600 to $1,000). Doing this yourself is difficult and dangerous because of the weight of the slab you cut loose. Cutting through concrete block is no picnic either. The two major tools you’ll need are a concrete saw and a hammer drill. Choose a concrete saw with either a 12-in. or a 14-in. blade. The 12-in. saw will work fine for an 8-in. thick wall.

We used a 14-in. saw because our wall contained both 8-in. and 12-in. blocks. Along with the saw, rent a diamond blade. This blade will pay for its higher cost in time saved because it cuts much faster than abrasive blades. Some rental stores carry only gas saws; others rent both gas and electric. We recommend electric so you won’t have to worry about fumes while you’re making the inside cut. Also, the electric saw is less bulky, making it easier to get in tight spaces. If you use the electric saw, especially if you wet the blade, plug it into a GFCI outlet to protect yourself from electrical shocks. These are big, heavy saws that take strength and attention to control. Always wear goggles, gloves and hearing protection when operating them.

When you rent the hammer drill, also rent a masonry drill bit long enough to go through the wall: 12 in. long for 8-in. block and 16 in. for 12-in. block. Expect to spend about $120 to $140 to rent the saw, hammer drill, diamond blade and masonry bit for the day. Having a helper spray water on the blade with a hand pump sprayer while you cut reduces the dust about 90 percent (Photo 6). But you’ll have to clean up a mucky mess on the floor.

Tip: Apply a bead of insulating foam to the floor to act as a curb to contain the water. Allow a day for the foam to harden.

For height accuracy, lay out your cutting lines on the inside wall (Photo 4). Since you have to cut from both the inside and outside, drill through the wall at the lower corners with a hammer drill held perfectly level, to establish the layout on the exterior. Or drill through the center of your proposed layout (Photo 4) if you build your window well first. That way you can adjust your layout to center the egress basement window on the well before drilling the corners (Photo 5).

Tip: Use the joints on the block to help maintain accurate alignment—if you can find them through the tar that’s often spread on the exterior!

Prevent Moisture Trouble—Establish Good Drainage

Any time you install an egress window below ground, you have to ensure good drainage. If your basement has ever had moisture problems, take these steps:

• Step 1: Make sure existing gutters and downspouts are clean and drain water away from the house. If necessary, install new gutters.
• Step 2: Check the grade of the slope around your foundation walls. It should be 1/2 in. per foot at least 10 to 12 ft. out from the foundation wall.
• Step 3: Make sure the drainage system is in good repair. Many homes have a drainage system around the footing of the foundation walls that sends excess water to a sump pump or exterior drain. If you have such a system and your soil has a high clay content, create a gravel drainage path below your window well to tie into this system.
• Step 4: If you’ve had moisture or flooding problems, consult a waterproofing specialist before adding a below-ground window.
  

  CAUTION!

  If you wet the blade to reduce dust, make sure you plug your concrete saw into a GFCI outlet to prevent a hazardous shock.

Roll up your sleeves and get to work

Complete the cut from the outside

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Finish cutting through the wall by making the same cuts on the outside wall. If you have a brick ledge like we did, some blocks will be 12 in. thick and some will be 8 in. Mark the lines for the outside cut with tape and cover the well area with a tarp to keep it clean.

Knock out the block

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Break out the block with a 4-lb. hammer, starting at the top center. Work carefully around the edges so you don’t loosen the remaining blocks. For stubborn blocks, first break out the core in the middle of the block, then break the block.

Smooth out the opening

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Chip the sides of the opening smooth with a brick chisel. Check to be sure the rough opening is large enough for the rough frame and basement window.

Fill the block cores with concrete

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Fill the open cores under the sill with concrete. Stuff newspaper into the cores to keep the concrete from falling down through them.

Install the sill

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Cover the wet concrete with plastic sheeting so the water from the concrete won’t warp the frame sill. Drive 3-in. deck screws partway into the treated wood sill and push them down into the wet concrete. The screws will anchor the sill and prevent the frame from shifting.

Frame the basement window opening

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Build the header according to your plan (we installed two), hoist it into place and screw it to the floor joists. Cut the frame sides to length for a very tight fit and bang them into place to support the header. Plumb the sides with a level and toe-screw them to the sill and header.

Anchor the frame to the block

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Anchor each side of the frame to the block wall with two 3/16 x 3-1/4 in. concrete screws. Predrill for the screws with a masonry bit. Countersink the hole for the screwhead with a 3/8-in. drill bit.

Caulk around the frame

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Seal gaps between the wood frame and the concrete with polyurethane or other exterior caulk. For gaps more than 1/4 in. wide, push a foam backer rod into the gap before caulking. With the frame securely in place, you can remove the temporary support wall. Once cut, the masonry blocks won’t fall out of the wall. You have to break them out with a 4-lb. hammer (Photo 8). Be sure to wear eye protection. Chips will fly! With the block broken out, you’ll see that your cuts won’t align perfectly. Smooth the sides as best you can with a brick chisel (Photo 9).

Photos 11 – 14 for setting the rough frame. Cut the pressure treated 2×10 to fit the thickness of your wall. Since we had both 8-in. and 12-in. thick blocks, we fit the window to the 8-in. thickness and mortared a beveled sill under the window to shed water over the 12-in. blocks (Photo 17).

Anchoring the rough frame to the block can be tricky (Photo 13). Mark the block where the concrete screws can get a good bite into solid concrete. Don’t try to draw the side frames tight to the wall with the screws. Use shims when tightening the screws to keep the frame straight and plumb (perfectly vertical).

Install the window and wall finishes

Install the basement window

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Center the window in the opening and level it with cedar shims. Get help here to steady the window while you shim it. Temporarily tack the shims in place and remove the window.

Caulk around the window

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Apply a generous bead of caulk around the treated wood frame to create a seal behind the nailing fin of the basement window. Set the window in place, check it for level, and drive screws or nails through the nailing fin to secure it to the frame. Some manufacturers specify that the fin must be nailed, not screwed.

Create a bevel in the ledge

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Bevel the ledge under the window with mortar so it will shed water. Use a straightedge as a guide because your saw cut won’t be perfectly straight. Wet the ledge, add the mortar and shape the bevel with a small finishing trowel. Installing the basement window (Photos 15 –17) will go quickly compared with the prep work. Most manufacturers include complete installation instructions with every window. Read through them to check for variations from our procedure. The trim work will vary according to the style of your home. The exterior finish could pose some problems because most foundation walls are coated with rubbery tar below the soil level. We chose to cover the entire exposed foundation around the window and inside the well with metal lath and stucco. If you have lap siding, you may choose to apply furring strips to the concrete and carry the lap siding down into the well area. On the interior, we trimmed the window with tile rather than the more traditional wood sill and casing; however, wood trim also will work well.

Egress Window Choices

Casement windows (windows that are hinged on one side and crank open) and side-to-side sliding windows are the best choices for egress basement windows. Double-hung windows (windows that slide up and down) don’t work well because they have to be almost 5 ft. tall in order to meet the minimum openable area requirements—more digging and a deeper well.

Sliding windows don’t have to be as tall as a double-hung, but they do need to be wide. It takes a 48 x 48-in. sliding window to meet the minimum egress requirements.

Casement windows are usually ideal because the entire window swings open. That means you can install a smaller casement window than other types. A 29-in. wide by 47-in. wide (outside frame dimensions) window will meet the requirements, and you can go even smaller if the window is equipped with special egress hinges. Modern casement windows with a single lock are also the easiest for a child to open. Check window sizes in manufacturers’ catalogs at any home center or window and door store for basement casement windows.

Additional Information

Fig. A: Window Framing Details

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