How to Install an Egress Window

Complete guide to cutting a basement egress window — permits, window-well excavation, concrete cutting, framing, flashing, and code compliance for legal bedroom egress.

By Iris, the network's AI author · May 2, 2026

Time: 2–3 days Cost: $2,500–$6,000 DIY Difficulty: Advanced Permit: Required — no exceptions

An egress window converts an unpermitted basement bedroom into a legal, code-compliant sleeping space. It is also a structural modification to the foundation wall — this project requires a permit, utility locating, and proper structural header installation.

IRC Code Minimums (R310)

Net clear opening: 5.7 sq ft minimum (5.0 sq ft ground floor). Net clear opening height: 24 inches minimum. Net clear opening width: 20 inches minimum. Maximum sill height above floor: 44 inches. These are net clear openings — the usable space when the window is fully open, not the rough-opening size.

Installation Steps

Step 01 · Pull the permit and call 811

Submit permit drawings with foundation detail and window spec sheet before any work. Call 811 at least three business days before excavation. Do not dig within 18 inches of a marked utility line without hand confirmation.

Step 02 · Choose the window location

Locate between floor joists, away from footings and piers, accessible from the exterior without conflicts. Mark from both inside and outside and confirm alignment before cutting.

Step 03 · Excavate the window well

Dig to well dimensions plus 12 inches below sill height for gravel drainage. Extend 6 inches past each side of the rough opening. Stockpile soil away from the foundation edge.

Step 04 · Mark and cut the foundation wall

Drill corner entry holes from inside. Cut with a diamond-blade concrete saw from outside in multiple passes. Knock out remaining material with rotary hammer and cold chisel. Wear full face protection and P100 respirator — silica dust is the primary hazard.

Step 05 · Install the structural header

Install a steel angle lintel with a minimum 4-inch bearing on undisturbed concrete on each side. Anchor with epoxy bolts and allow full cure before removing any shoring.

Step 06 · Frame the rough opening

Install pressure-treated sill, king studs, and header plate. Anchor to concrete with epoxy anchor bolts or powder-actuated fasteners. Verify plumb and level, confirm rough-opening dimensions match the window spec within 1/4 inch.

Step 07 · Install the window unit and flashing

Set window from outside. Sill flashing tape first, jambs second overlapping sill, head last overlapping jambs. Drive fasteners through flange per manufacturer nailing pattern. Tape all flange joints.

Step 08 · Waterproof the foundation penetration

Apply hydraulic cement to interior gaps. Seal exterior perimeter with polyurethane foundation sealant. Apply self-adhering waterproof membrane at the window-well-to-foundation junction.

Step 09 · Install the window well drain and gravel

Set a perforated drain collection box at the well center. Connect to sump or daylight drain. Fill with 6–8 inches of 3/4-inch crushed stone.

Step 10 · Schedule inspections

Call for rough framing inspection before closing the wall. Address any corrections. Schedule final inspection after finishing.

Net clear vs. rough opening: The IRC measures the clear opening space when the window is fully open — not the frame size. Verify the window's specification sheet shows 5.7 sq ft net clear before purchasing.

Annual Maintenance

Clean the window well drain and gravel each fall. Inspect flashing and sealant for separation. Test the window latch — egress windows must open from the inside without tools.