An egress window is what makes a basement bedroom legal. The Ontario Building Code requires every sleeping area to have a window large enough to escape through during a fire — minimum 5.7 square feet of openable area, with a minimum 24-inch height and 20-inch width. Below-grade basement windows must also have a window well that allows the person to exit and a method to climb out (steps or a ladder built into the well).

This guide covers the full retrofit process: cutting through a concrete foundation wall, framing the new opening, installing the window, excavating and building the window well, and waterproofing. This is one of the most involved DIY projects a homeowner can attempt — it crosses framing, masonry, exterior waterproofing, and excavation, and requires a permit. For most homeowners the right answer is to hire it out, but the work is technically possible to DIY for confident, mechanically-skilled owners with appropriate tools.

Before you start

Six things to confirm before any concrete gets cut:

1. Permit is mandatory. Cutting a foundation wall and creating an egress opening is a structural alteration. Ottawa requires a building permit, engineered drawings stamped by a structural engineer, and inspections at framing and final stages. Working without a permit is a code violation that can void home insurance and complicate resale. The permit is non-negotiable.

2. Window size meets code. Ontario Building Code 9.9.10.1 requires: minimum 0.35 square metres (3.77 sq ft) opening, minimum 380 mm (15 inch) opening dimension, openable from inside without tools or special knowledge. For sleeping rooms specifically, the unobstructed openable area must allow exit by an adult. Most building departments enforce 5.7 sq ft as the practical minimum. Confirm exact requirements with your specific building permit reviewer.

3. Locate underground utilities (Ontario One Call). Before any excavation, call Ontario One Call (1-800-400-2255) to mark underground utilities. Free service, takes 5 business days for utilities to mark. Hitting a buried gas line, water main, or electrical service is a serious safety hazard and a legal requirement violation. Plan around marked utility locations or relocate the window position.

4. Foundation type and structural assessment. Concrete (poured or block) foundations need different cutting approaches. Poured concrete uses a wet-cut concrete saw with diamond blade. Block foundations can be cut with the same tools but joint locations affect cutting plan. Either way, an engineer must specify a structural lintel (header) above the new opening that transfers the load above. Lintel sizing depends on what's above (one storey vs two-storey vs full house).

5. Window well dimensions and drainage. Window wells for egress must be at least 36 inches deep (front-to-back from the foundation), 36 inches wide, and equipped with a means of climbing out (steps or ladder). Ontario code also requires drainage — wells fill with water during heavy rain unless drained to weeping tile or a French drain. Plan the well dimensions and drainage path before starting.

6. Tools and equipment scale. Concrete cutting requires a wet-cut concrete saw with a diamond blade. Excavation needs a mini-excavator for any reasonable depth. Without these tools, the job becomes manual labour spread over weeks. Budget for tool rental and plan equipment delivery.

What you'll need

Tools

Wet-cut concrete saw with diamond blade (rented)
Mini-excavator or skid-steer (rented)
Hammer drill with masonry bits
Sledgehammer (for breaking out cut sections)
Pry bar
Reciprocating saw with metal blade (for cutting reinforcing bar)
Tape measure (long, 25-foot+)
4-foot level and laser level
Chalk line
Heavy-duty ear protection and eye protection
Respirator rated for silica dust
Safety harness if working in deep excavation
Standard framing tools: drill, circular saw, hammer
Caulk gun
Trowel for any cement work

Materials

Egress-rated window unit (vinyl casement or slider, sized to OBC requirements)
Engineered structural lintel (steel, concrete, or LVL per engineer specification)
PT lumber for framing (#2 or better)
Standard SPF lumber for cripples and headers
Insulation (for the new framed opening, R-22+ for basement)
Pre-fab window well (galvanized steel) OR poured concrete well per design
Window well cover (clear polycarbonate, code-compliant for egress)
Window well ladder or integrated steps
Drainage gravel (3/4 clear) and 4-inch perforated drain pipe
Filter fabric (geotextile)
Self-adhered membrane flashing for window perimeter
Exterior waterproofing membrane for foundation
Backfill material
Spray foam insulation (for window perimeter air seal)
Concrete patching mortar (if patching cut edges)

If you've never cut concrete before, hire a concrete-cutting contractor

Concrete cutting is loud, dusty (silica dust is a serious lung hazard), and physically demanding. The diamond blade saws weigh 30+ pounds, generate intense vibration, and require water cooling that creates slurry. A professional concrete-cutter does an egress-window cut in 4 to 8 hours, and the quoted price reflects saw rental, blade wear, dust control, and the structural care the cut demands.

DIY concrete cutting saves money but adds 2 to 3 days of physical labour, requires properly-rated PPE for silica dust, and one wrong cut creates a structural problem. For most homeowners, hiring this single trade while DIYing the framing and finishing work is the right balance.

Step-by-step instructions

Apply for permit and engineered drawings

Hire a structural engineer to design the opening and specify the lintel. The engineer reviews what's above the proposed opening (joists, floors, walls) and sizes the structural beam that will carry that load above the new window.

Submit the engineered drawings plus a permit application to Ottawa via MyServiceOttawa. Permit review takes 4 to 10 weeks. Don't start any work until the permit is in hand — work without a permit can be ordered to stop and may have to be undone for inspection.

Call Ontario One Call (free utility locate)

Call 1-800-400-2255 at least 5 business days before excavation. Provide the address and approximate excavation area. Within 5 business days, utilities (Hydro Ottawa, Enbridge gas, water, telecom) come out and mark their underground service locations with paint or flags.

Plan around marked locations. If a utility runs through your planned excavation, you must either relocate the window or have the utility relocated (utility-paid only in some cases; usually homeowner-paid).

Excavate the window well

Use a mini-excavator or skid-steer to dig the window well excavation. Depth is typically 6 to 8 feet from grade (matching the window sill height below grade). Width and length match the planned window well dimensions plus working room.

Dig with care near the foundation — equipment buckets can damage foundation waterproofing. Hand-dig the last 6 to 12 inches against the foundation wall.

Pile excavated soil away from the foundation in a location where it can be brought back to backfill at the end of the project.

Mark and cut the foundation opening

From the inside, mark the opening dimensions on the foundation wall per the engineer's drawings. Add 1/2 inch on each side for framing tolerance.

From the outside (in the excavated well), score the cut line with a smaller masonry blade first, then make full-depth cuts with the wet-cut concrete saw. Multiple passes — don't try to cut full depth in one pass.

Maintain water flow during cutting to control silica dust and keep the diamond blade cool. Wear silica-rated respirator throughout.

Remove the cut concrete section

Once cuts are complete on all four sides of the opening, the cut concrete section needs to be removed. For most foundations this is a 200 to 400 lb chunk.

Use a sledgehammer to break the section into smaller pieces — start at the corners. Pry the pieces out with a pry bar.

Cut any reinforcing bar (rebar) within the opening with a reciprocating saw using a metal-cutting blade.

Install the structural lintel

Following the engineer's drawings exactly, install the specified lintel over the opening. This typically means temporarily supporting the load above (with screw jacks or temporary bearing walls) while the lintel is installed.

Lintels are usually steel I-beams or LVL beams. They sit on solid bearing points on each side of the opening (typically the original foundation wall extending past the opening, or pocket-cut into the foundation as the engineer specifies).

Schedule the framing inspection at this stage. The inspector verifies that the lintel matches the engineered drawings before any framing or finish work proceeds.

Frame the rough opening

Frame the rough opening for the window with PT lumber on the bottom (sill plate) and standard SPF for jacks and king studs. The rough opening dimension is typically the window unit width + 1/2 inch and the unit height + 1/2 inch.

Square the rough opening — diagonal measurements should match. Out-of-square openings produce windows that don't operate smoothly.

Install header above the rough opening per engineering specs (this may be redundant with the lintel if the lintel itself acts as the header — engineer will specify).

Install the window unit

Apply self-adhered membrane flashing around the rough opening before installing the window. Flashing prevents water from entering the wall cavity around the window perimeter.

Insert the window unit into the rough opening from the outside. Centre it in the opening with shims under the bottom and on each side. Fasten through the window's nailing flange (or interior brackets, depending on window type) into the framing.

Verify level and plumb at multiple points before final fastening. Operate the window — if it binds or doesn't seal, the rough opening is not square.

Apply additional flashing over the nailing flange to ensure water can't penetrate behind.

Install the window well

Pre-fab galvanized steel window wells are the easiest option — they bolt to the foundation with concrete anchors and have integrated steps or ladder. Position the well so its top edge sits at or above grade and its bottom is below the window sill.

Drill anchor holes in the foundation per the well manufacturer's spec. Drive the anchors and bolt the well in place.

Alternative: poured concrete window well (more work, more permanent, more expensive). Form, pour, and finish per design.

Install drainage at the bottom of the well

Lay 4 to 6 inches of 3/4 clear gravel at the bottom of the window well. Run a 4-inch perforated drain pipe from the well, sloped down to either:

Daylight drainage: a graded outlet point on your property where water can drain away from the foundation (slope at least 2% for the entire run).
Weeping tile connection: if your foundation has weeping tile, tie the drain into it. This is typically how new installations handle it but requires opening the weeping tile system.
Sump pit: some installations route the drain into a sump pit, where a sump pump removes the water. This requires power for the pump.

Waterproof the foundation around the new opening

Apply exterior waterproofing membrane (rubber-bitumen membrane like Blueskin or equivalent) to the foundation wall around the new opening. The membrane creates a waterproof barrier between the soil and the foundation.

Extend the membrane at least 12 inches past the opening on all sides. Seal the membrane to the foundation thoroughly with the manufacturer's primer and rolled-on adhesive.

This step is what prevents water intrusion through the new opening over the next 30 years.

Backfill and finish

Place wrap drainage rock around the foundation drain pipe. Then backfill in lifts (12-inch layers, compacted by foot or with a small compactor) until grade is reached.

Slope the final grade away from the foundation at least 5% for the first 6 feet to direct surface water away.

Inside, frame around the new opening to integrate with the basement framing, install insulation in the framed cavity (R-22+), apply vapour barrier, and drywall.

Schedule the final inspection. The inspector verifies the window meets egress requirements, the well meets size and drainage requirements, and finishing meets code.

Install the window well cover (egress-compliant)

An egress window well must have a cover that's removable from inside without tools or special knowledge — the cover is part of the egress path.

Code-compliant covers are clear polycarbonate or galvanized grates with quick-release latches operable from below. Lockable from above to prevent unauthorized entry, but quickly removable from below for emergency exit.

Install per the cover manufacturer's spec. Test the release mechanism — confirm an adult can operate it without instructions or tools.

Common mistakes that cost you

Skipping the permit. Cutting a foundation wall without a permit is a major code violation, voids home insurance, and complicates resale. The permit and engineer's drawings are small relative to the overall work scope and protect against legal and insurance issues.
No engineered drawings for the lintel. The lintel carries everything above the opening — floors, walls, roof. Sizing it wrong causes structural failure (in extreme cases, the floor above sags or cracks). Always have a structural engineer specify.
Skipping Ontario One Call. Hitting a gas line, water main, or electrical service can be fatal. The locate is free, takes 5 business days, and is required by law. Never excavate without it.
Inadequate drainage in the window well. Wells fill with water during heavy rain and freeze in winter, eventually breaking the well or finding their way through the window seal. Always plumb the well to weeping tile, sump, or daylight.
Not waterproofing the foundation around the new opening. Cutting through the foundation creates new water entry paths. Apply exterior waterproofing membrane around the entire opening before backfilling.
Unworkable window cover. Code requires the well cover to be removable from inside without tools. Permanent or hard-to-remove covers fail egress requirements regardless of well dimensions.
Working without silica respirator. Concrete dust contains silica, which causes serious lung disease over time. Always wear a NIOSH-rated respirator while cutting concrete.
Backfilling without drainage rock around the foundation. Drainage rock provides a path for groundwater to reach the drain pipe. Without it, water saturates the soil against the foundation and finds its way inside.

Frequently asked questions

How much does an egress window installation cost?

Pricing depends on foundation type, excavation depth, drainage complexity, and finish level. The main cost drivers are concrete cutting, the window unit, well and drainage work, structural engineering, the building permit, and framing and finishing. Each scales with site conditions and how much the opening disturbs the surrounding structure.

DIY can reduce labour cost but adds substantial time and tool rental. For most homeowners, the math favours hiring out at least the concrete cutting and structural work. We provide a detailed written breakdown so you see exactly what is included before any work begins.

What size window meets egress requirements?

Ontario Building Code 9.9.10.1: minimum 0.35 square metres (3.77 sq ft) openable area with minimum 380 mm (15 inch) dimension. Practical interpretation by most building reviewers: minimum 5.7 sq ft openable area with 24-inch minimum height and 20-inch minimum width.

The window must be openable without keys, tools, or special knowledge from inside, and the openable portion must be unobstructed. Slide-up double-hung windows often don't meet egress because the opening is half the window's height.

How deep can a basement be and still allow an egress window?

Window sill must be no more than 1.5 m (about 5 feet) above the floor of the room, AND the sill must allow for the required well dimensions. In very deep basements, the sill might need to be near floor level.

If the existing basement is too deep for an egress window to work geometrically, alternatives include adding an egress door (full walkout) or building a more elaborate well with steps.

Can I install an egress window in winter?

Technically yes, but the work is much harder. Frozen ground requires specialized excavation; concrete cutting in cold weather requires water management to prevent freezing on equipment; concrete patching requires temperature controls.

Most contractors avoid egress installs from December through March in Ottawa. If you must do it in winter, expect 30-50% premium pricing and longer schedules.

What's the difference between a window well and a walkout?

A window well is a depression in the ground around a basement window, allowing the window to be partially or fully below grade while still functioning. Wells are 36 inches minimum for egress.

A walkout is a basement door at grade level (because the lot slopes), allowing direct exit from the basement. Walkouts don't need wells but require excavation to create the slope. Walkouts are more expensive but provide better egress and natural light.

Do I need an egress window for a basement bedroom that has a walkout door?

If the bedroom has direct access to the walkout door (door from the bedroom or directly off the bedroom's hallway with a clear path), the walkout serves as the egress and a window is not separately required.

If the bedroom is isolated from the walkout (separated by another room or significant distance), code typically requires the bedroom to have its own egress means — either a window or a direct door.

How does the egress window affect my home's value?

Adding a legal egress window to a basement bedroom converts it from non-habitable to habitable space, adding legal square-footage value at resale. The conversion turns a 'rec room' into a 'bedroom' on appraisals and listings.

If you're finishing a basement to add bedrooms for resale value, the egress window is typically one of the highest-return items in the project because it unlocks the bedroom designation appraisers and buyers look for.

When to call us instead

An egress window install crosses concrete cutting, structural engineering, excavation, waterproofing, and finishing. Each one is a different trade, and getting any of them wrong creates expensive problems. Concrete cutting alone is dangerous if you're not trained — silica dust, vibration, and the weight of the saw require respect.

We do egress window installs as part of basement renovations and as standalone scopes. We coordinate the engineer, the permit, the cutter, the excavator, the framer, and the inspector — so the homeowner has one point of contact and a fixed-price quote. For most homeowners this is the right answer.

Book a free 60-minute site visit →

Related Ottawa services

Egress windows are part of legal basement bedroom conversion. Our basement renovation team handles egress, framing, electrical, plumbing, and finishing as a fixed-price project with permits and inspections coordinated. Book a free 60-minute consultation.