Window Well Size: How Wide and Deep Your Well Should Be

A window well that is too narrow or too shallow causes problems out of proportion to its cost. Water pools against the glass, soil spills over the edge, and the basement stays dark. Getting the window well size right comes down to three measurements: how much wider the well is than the window opening, how far it projects out from the foundation, and how far it extends below the sill. Egress wells for basement bedrooms add a fourth requirement, enough floor area for a person to climb out.

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For a typical basement hopper or slider, choose a well at least 6 inches wider than the window opening (3 inches past each side), a projection of 12 to 24 inches from the wall, and a depth that reaches about 8 inches below the window sill, with the top sitting 3 to 6 inches above finished grade. Egress wells are much larger: generally at least 9 square feet of floor area, with a projection of at least 36 inches and a width of at least 36 inches, plus a permanent ladder or steps when the well is deeper than about 44 inches.

How to Determine Window Well Size

Window well size always starts with the window, not the well. Measure the width of the foundation opening, including the frame, and the distance from the sill to the ground outside. Then work through each dimension.

Width beyond the window

The well’s inside width should exceed the window opening by at least 3 inches on each side, so 6 inches total. Many installers prefer 6 inches per side when space allows, since it lets more light in and keeps the frame clear of soil and leaves. A 32-inch-wide basement window, for example, pairs well with a well about 38 to 44 inches wide. Wells are sold by width, commonly in sizes like 36, 42, 48, 60 and 72 inches, so pick the next size up from your minimum.

Projection from the foundation

Projection is how far the well sticks out from the wall. Standard non-egress wells usually project 12 to 18 inches for small windows and up to 24 inches for larger ones. More projection means more light and easier cleaning, but it takes up yard space and may conflict with walkways, decks or air conditioner pads.

Depth below the sill

The bottom of the well should extend at least 8 inches below the window sill, which leaves space for a gravel drainage bed beneath the sill line. The top of the well should rise about 3 to 6 inches above the surrounding grade so surface water does not flow in. Add those numbers together: if the sill sits 30 inches below grade, you need a well roughly 30 + 8 + 4 = 42 inches tall. Wells are sold in heights such as 24, 36, 48 and 60 inches, and you can stack or overlap some styles for deeper installs.

Egress Window Well Rules

A bedroom in the basement needs an emergency escape route, and the window well is part of it. Requirements vary by jurisdiction, so treat this as a general description and confirm locally. Common provisions include:

• Minimum floor area: about 9 square feet inside the well.
• Minimum projection and width: about 36 inches each, measured from the foundation and side to side.
• Ladder or steps: required when the well depth exceeds roughly 44 inches. The ladder must be permanently attached and must not obstruct the window opening when it is fully open.
• Clear opening for the window: the well must let the egress window open fully so a person can pass through.
• Covers: must be removable from inside without tools, keys or special knowledge.

Egress wells come in many forms: corrugated galvanized steel, molded plastic or fiberglass with built-in steps, terraced landscape blocks and poured concrete. A galvanized window well is the most common budget option, while molded and terraced versions look more finished and often include integrated steps.

Materials and Shapes

• Galvanized steel: affordable, strong and widely available in standard sizes. Corrugations add stiffness. Expect some surface oxidation over many years.
• Molded polyethylene or composite: lighter, often textured to look like stone, and available in egress versions with steps.
• Concrete or masonry block: durable and customizable but heavier and more labor-intensive.
• Wood timbers: rare now, since they rot and attract insects.

Shapes include semicircular, rectangular and stepped (terraced). Rectangular wells maximize floor area for egress, while semicircular wells suit smaller hopper windows and shed soil pressure evenly.

Step-by-Step Installation Guide

Installing a standard well around an existing basement window is a manageable weekend project. Egress wells are larger and usually part of a permitted egress window job.

1. Call 811 a few days before digging so buried utilities are marked.
2. Mark the outline of the well, adding about 12 inches of working room beyond its projection and width.
3. Excavate to the depth of the well plus 6 to 12 inches for gravel. Slope the excavation sides back if soil is loose to prevent collapse.
4. Check that the foundation drain or a dedicated well drain is accessible. Many installers run a perforated pipe vertically from the footing drain up to the well floor.
5. Set the well against the foundation, centered on the window and level across the top.
6. Drill the foundation and fasten the well flanges with masonry anchors spaced per the manufacturer’s directions. Wear eye protection and a dust mask, and use a wet method or dust collection when drilling concrete.
7. Backfill around the outside of the well in layers, tamping gently so the walls do not bow inward.
8. Fill the inside of the well with 6 to 12 inches of washed gravel, keeping the top of the gravel at least 3 inches below the sill.
9. Regrade the yard so the soil slopes away from the well and the house.
10. Add a cover if desired.

Covers, Drainage and Trip Safety

An open well creates a fall and trip hazard, especially for children, pets and guests walking at night. A sturdy cover rated for the expected load keeps people from stepping in, and clear polycarbonate covers let light through. Grates work well where snow load is a concern. For egress wells, the cover must lift from inside easily without tools.

Keep the area around the well tidy. Set the well rim slightly above grade but not so high that it becomes a tripping edge in a mowed lawn, and avoid placing wells across walkways. If a well sits near a path, add landscape edging or a low planting bed so people naturally step around it. Mark the location of the well before winter if snow hides it.

Drainage is the other half of the job. A well without a drain or gravel bed fills with water during heavy rain and can push water through the window frame. Make sure gutters and downspouts discharge well away from the well, and clean leaves and debris from the gravel each season.

Troubleshooting Window Well Problems

• Water pooling at the bottom: the gravel is clogged or there is no drain. Clean the gravel or add a vertical drain to the footing tile.
• Well walls bowing inward: soil pressure is too high for the material, or backfill was compacted too hard. Add bracing or replace with a heavier gauge or reinforced unit.
• Soil washing in at the edges: the top of the well sits too low. Raise it or add an extension so it stands 3 to 6 inches above grade.
• Window still dark: the well is too narrow or the walls are dull. A wider well, light-colored liners or a clear cover help.
• Gaps between well and foundation: add anchors and seal with exterior-grade sealant.

Cost Ranges and When to Call a Pro

A standard galvanized well for a small basement window usually costs from about fifty to a couple hundred dollars, with molded and decorative wells costing more. Egress wells run from a few hundred to well over a thousand dollars for the unit alone. Professional installation of a standard well is often in the few hundred dollar range, while a full egress window and well installation with excavation, foundation cutting and finishing usually costs several thousand dollars.

Call a contractor when you need a new egress opening cut into the foundation, when the excavation will be deeper than about 4 feet (trench collapse becomes a serious risk), when the soil is saturated or unstable, or when you see cracks in the foundation wall near the window. Permits are commonly required for egress work, and some areas require inspection of the well and window together.