Can I use an existing small basement window as egress by enlarging the opening?

Yes, enlarging an existing small basement window opening to meet egress requirements is one of the most common approaches to egress window installation in Metro Vancouver — and it is typically less expensive than cutting a completely new opening because part of the foundation wall has already been removed. However, this is still structural work that requires engineering, a building permit, and a qualified contractor.

Most older homes across Metro Vancouver — particularly post-war homes from the 1950s through 1970s in Burnaby, New Westminster, North Vancouver, and Coquitlam — have small basement windows that were never designed for egress. These original windows typically measure 600 to 800 millimetres wide by 300 to 400 millimetres tall, well below the BC Building Code requirement of 0.35 square metres of unobstructed opening with a minimum width of 380 millimetres and maximum sill height of 1,100 millimetres. Enlarging these existing openings to meet code is the logical approach because the foundation wall already has a penetration in approximately the right location.

The enlargement process involves several steps. A structural engineer must first assess the existing opening, the foundation wall condition, the loads above, and the soil conditions to design the new, larger opening with an appropriate lintel or header. In BC's seismic zone, this engineering must account for earthquake loading, which adds design requirements not found in Eastern Canada. The engineer's fee for this work typically runs $500 to $1,500 in Metro Vancouver. With the engineered design in hand, your contractor applies for a building permit from your local municipality.

The cutting work itself requires temporary shoring above the existing opening before any enlargement begins. The contractor then saw-cuts the concrete (or removes concrete blocks, depending on your foundation type) to the engineered dimensions, installs the structural header, frames the rough opening, and installs the new egress-rated window. The exterior work includes excavating for the window well, installing the well structure, placing drainage gravel connected to the weeping tile system, backfilling, and grading.

Direction of Enlargement

An important engineering decision is which direction to enlarge — wider, taller, or both. Widening the opening is generally preferred because it maintains more of the existing foundation wall below the opening, preserving the structural integrity of the lower wall section. Cutting downward to lower the sill height is sometimes necessary if the existing window sits too high to meet the 1,100mm maximum sill requirement, but lowering the opening reduces the amount of concrete between the bottom of the window and the footing — and if you cut too close to the footing, you risk compromising the foundation's bearing capacity. The structural engineer will determine the safe limits based on your specific foundation.

Enlarging an existing opening in a poured concrete foundation typically costs $2,500 to $6,000 in Metro Vancouver — toward the lower end of the $3,000 to $8,000 range for a completely new opening. The savings come from less concrete cutting and smaller window well excavation. For concrete block foundations, the cost is similar but the work requires more precision to avoid cracking blocks beyond the intended opening.

One critical detail in Metro Vancouver's climate: when you enlarge the opening, the existing waterproofing around the old window is disturbed and must be completely redone. The new window frame needs proper flashing, sealant, and exterior waterproof membrane extending into the window well. Given Metro Vancouver's 1,200+ millimetres of annual rainfall, any gap in the waterproofing envelope around the enlarged opening will leak during the first wet season. Insist that your contractor waterproofs the full perimeter of the new opening, not just the areas where new cutting was done.

A building permit is required for this work, and your municipality will inspect at the rough-in stage before drywall. Do not skip the permit — unpermitted structural modifications to a foundation wall create liability issues, insurance complications, and resale problems. Find a qualified contractor for your egress window project through Vancouver Basement Finishing for a free estimate.

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