What is the minimum opening size required for a basement egress window in New Brunswick and how is it measured?

The minimum unobstructed opening size for a basement egress window in New Brunswick is 3.8 square feet (0.35 square metres), and it is measured as the clear, free area available when the window is fully open — not the glass size, not the frame size, and not the rough opening in the wall. This measurement determines whether an adult can physically escape through the window in a fire or emergency, which is why the code is strict and specific.

The clear opening is the space you could actually fit through with the window fully opened. For a casement window (which swings outward on a hinge), the clear opening is essentially the full frame opening minus any hardware or obstructions. For a sliding window, the clear opening is only the portion that slides open — typically half the total window area. For an awning window (hinged at the top, swinging outward from the bottom), the clear opening is the gap created at the bottom when fully extended. This is why casement windows are the preferred choice for basement egress — they provide the maximum clear opening relative to the overall window size.

To measure whether your existing window meets the requirement, open the window fully and measure the width and height of the unobstructed opening in metres or inches. Multiply width by height to get the area. For example, a window that opens to a clear space of 24 inches wide by 24 inches tall gives you 576 square inches, which is 4.0 square feet — this passes. A window that opens to 20 inches by 24 inches gives 480 square inches or 3.33 square feet — this fails. Many homeowners are surprised to find that their existing basement windows, even large-looking ones, do not meet egress requirements when actually measured in the open position.

Beyond the area requirement, the NB Building Code also requires a maximum sill height of 1,500 mm (approximately 59 inches) from the finished floor to the bottom of the window opening. This ensures a person can reach and climb through the window without a ladder. If your basement has been finished with a raised subfloor (like Dricore panels), the sill height is measured from the top of the finished floor, not the concrete slab — which means a raised floor effectively reduces your available sill height. Measure carefully before finalizing your floor assembly.

The window must also be operable from the inside without tools, keys, or special knowledge. A child or a disoriented person in a smoke-filled room must be able to open the window. Any locking mechanism must release with a simple, intuitive motion.

If your existing basement window does not meet the 3.8 square foot clear opening, you have two options: enlarge the existing opening in the foundation wall, or cut a new, larger opening in a different location. Both involve cutting concrete, installing a structural lintel, adding a window well with drainage, and waterproofing the perimeter. In the NB market, this runs $2,500 to $5,000 per window installed.

When shopping for egress windows, always check the manufacturer's specification sheet for the clear opening area — it will be listed separately from the overall frame dimensions. Do not assume a window meets egress requirements based on the frame size alone. Your building inspector in Moncton, Fredericton, Saint John, or your Regional Service Commission will measure the actual clear opening during inspection, and if it falls short, the installation fails regardless of what the window looked like on paper.

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