Basement Egress Windows: Code Requirements, Installation, and Well Construction

Code Requirements (IRC)

Minimum net clear opening: 5.7 square feet (5.0 square feet for ground-floor windows, but basement egress is almost always 5.7).

Minimum opening height: 24 inches. Minimum opening width: 20 inches. You cannot meet the 5.7 square foot requirement with both dimensions at minimum — one must be larger.

Maximum sill height: 44 inches from the finished floor. The window must be reachable without a step stool.

The window must open from the inside without tools, keys, or special knowledge. Casement and sliding windows that meet the size requirements work. Double-hung windows rarely meet the minimum because only one sash opens.

These are IRC (International Residential Code) minimums. Your local jurisdiction may have additional requirements. Check before ordering the window.

Planning the Installation

Choose the window location based on: where the bedroom will be, what is on the outside (avoid locations under decks, porches, or driveways), and what is on the inside (avoid locations where plumbing, electrical panels, or HVAC are in the wall).

The window well outside must be large enough for a person to stand in. If the well is deeper than 44 inches from the ground surface, it must have a permanently attached ladder or steps. The well floor must drain — standing water in the well defeats the escape purpose.

Permits: an egress window installation requires a building permit in virtually all jurisdictions. The permit process typically requires a plot plan showing the well location and a specification sheet for the window showing it meets the minimum opening requirements.

Cutting the Foundation Wall

This is the most intimidating part and the reason many homeowners hire this step out. Cutting through a concrete or block foundation requires a concrete saw and produces enormous amounts of dust.

Mark the opening on the interior wall. The rough opening should be 3-4 inches wider and taller than the window frame to allow for shimming and insulation. Drill pilot holes at the corners from inside.

From outside, use a concrete cut-off saw with a diamond blade to cut along the marked lines. A poured concrete wall needs a saw that cuts at least half the wall thickness from each side. Block walls can be cut from one side.

Remove the cut section. For poured concrete, this may require breaking it into pieces with a sledgehammer. For block, remove blocks one at a time. The lintel above the opening supports the wall load — install a precast concrete lintel or a steel angle before removing the block below it.

Window Well Installation

Excavate outside the opening to the required depth — the bottom of the well must be below the window sill. The well should be at least 36 inches wide (measured from the foundation wall) for comfortable escape, and as wide as the window opening.

Install 4 inches of gravel at the bottom of the well for drainage. If the soil drains poorly, install a drain line from the well bottom to a sump pump or daylight outlet. Water pooling in the well during rain is a serious problem — address drainage before finishing.

Set the window well form (corrugated galvanized steel or molded plastic) against the foundation wall. Secure it to the foundation with masonry screws and brackets. Backfill behind the well form with gravel for additional drainage.

A window well cover (clear polycarbonate dome) keeps rain, snow, and debris out while allowing light in and emergency escape. The cover must be openable from inside the well without tools.

Window Installation

Set the window in the rough opening. Shim it level, plumb, and square. Leave 1/4-3/8 inch gap on all sides for insulation and adjustment.

Fasten the window to the foundation with concrete screws (Tapcon or similar) through the window flange or frame. Pre-drill the concrete with a hammer drill and masonry bit.

Insulate the gap between the window frame and the concrete with low-expansion spray foam (window and door rated — standard expanding foam can bow the frame). Apply in thin beads.

Waterproof the exterior joint between the window flange and the foundation with a flexible waterproofing membrane or sealant. This joint is below grade and will see water pressure — it must be watertight.

Tools and Equipment

Concrete cut-off saw with a diamond blade (rent for $100-150/day). Hammer drill with masonry bits. Sledgehammer and cold chisel for breaking out the concrete. Level, tape measure, and shims. Low-expansion spray foam. Concrete screws and drill.

For excavation: shovel, wheelbarrow, and a strong back. A small excavator or a crew helps significantly for deep wells in heavy clay soil.

Safety equipment: concrete cutting produces silica dust, which causes silicosis with repeated exposure. Wear a P100 respirator, safety glasses, hearing protection, and gloves. Work in a well-ventilated area.

Frequently Asked Questions