What is the maximum sill height from the basement floor to the bottom of an egress window allowed by NB building code?

The maximum sill height from the finished basement floor to the bottom of the egress window opening is 1500mm (approximately 59 inches or 4 feet 11 inches) under the NB Building Code. This measurement is taken from the finished floor surface to the bottom of the clear opening — not to the bottom of the window frame, but to where a person could actually climb through.

This 1500mm maximum exists for a critical life-safety reason: in an emergency such as a fire, a person — including a child — must be able to reach and climb through the egress window without assistance. If the sill is higher than 1500mm, it becomes extremely difficult for occupants to escape, particularly in smoke-filled conditions where visibility is zero and panic reduces coordination.

In practice, most NB basements have foundation walls that place the existing small windows fairly high on the wall, often near the ceiling of a standard 7-8 foot basement. When converting to an egress window, the contractor typically cuts the opening downward from the existing window location to bring the sill within the 1500mm maximum. This is one reason egress window installations require careful planning — you need enough foundation wall below the opening to maintain structural integrity, and the bottom of the opening must clear the exterior grade and footing level.

If your basement has a finished floor that is lower than the original concrete slab — for example, if the basement was underpinned or the floor was lowered — the sill height measurement starts from the new finished floor level. This can actually make compliance easier because the lower floor increases the distance from floor to existing window height. Conversely, if you install a Dricore subfloor system (which raises the floor by about 25mm), you are slightly reducing the available sill height, though this amount is negligible.

For basements with low ceilings — common in older Moncton, Fredericton, and Saint John homes where ceiling height may be only 6.5-7 feet — the 1500mm sill height is rarely an issue because the foundation walls are shorter and the windows are proportionally closer to the floor. The bigger challenge in low-ceiling basements is often meeting the minimum clear opening size of 3.8 square feet while keeping the top of the window below the sill plate and floor joists above.

If your existing window sill exceeds 1500mm from the floor, you have two options. The first and most common is to enlarge the opening downward by cutting more foundation wall. The second is to build a permanent platform or step beneath the window, though this approach has limitations — the platform must be permanently attached, not furniture or a removable step, and some inspectors may not accept it depending on design. Cutting the opening lower is the cleaner, more universally accepted solution.

During your building permit inspection, the municipal inspector in Fredericton or Moncton (or the RSC inspector in rural areas) will measure this sill height as part of the final sign-off. Getting it right the first time avoids costly rework. Your contractor should verify the measurement before closing up any interior finishing around the window.

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