The short answer
A secondary suite bedroom in BC needs an egress window with at least 0.35 square metres of clear opening and no dimension smaller than 380 millimetres, openable from inside without keys or tools. Below-grade windows need 760 millimetres of clearance in the window well. Enlarging an undersized basement window typically costs $3,500 to $8,000 including foundation cutting.
The minimum size, in real terms
BC Building Code requires every bedroom in a secondary suite to have at least one window or exterior door that opens from the inside, with a minimum clear opening of 0.35 square metres and no single dimension smaller than 380 millimetres. That's not the frame size. It's the clear, openable area a person could actually climb through in an emergency.
A lot of original basement windows in North Shore homes built in the 1960s through 1980s are sliders or awning-style units sized around 24 by 18 inches, which doesn't come close. The math matters here: a window that looks like a reasonable size on the wall often fails the calculation once you measure the actual clear opening, not the frame.
Window wells: the clearance rule
If the egress window sits below grade, which is the case for most basement suites, it opens into a window well rather than open air. BC code requires at least 760 millimetres of clearance in front of that window, measured from the window to the well wall, so a person has room to actually get out, not just push the window open.
On a lot of North Shore properties, the existing window well is undersized or the window sits close to grade with no well at all, meaning a new one has to be excavated and installed. This is foundation-adjacent work, and it often gets bundled with the fire separation and drainage scope rather than priced as a standalone item.
Operation: no keys, no tools, no removing hardware
The egress window has to open from the inside without a key, a tool, or removing a sash or screen. This rules out a few things that show up in older houses more often than you'd expect: painted-shut original windows, security bars without an interior quick-release, and units where the screen has to come out before the sash will move.
If your basement has a security grille or bars over the window, which is common on North Shore properties near greenbelts or with a history of break-ins, the grille needs a release mechanism operable from inside without tools. A fixed grille bolted from outside doesn't meet code no matter how large the window opening is.
What it costs to fix an undersized window
Enlarging an existing basement window opening to meet egress size, including cutting the foundation wall, a new larger window unit, and a code-compliant window well, typically runs $3,500 to $8,000 per window. The range depends on how much concrete has to be cut, whether the foundation is poured concrete or block, and whether a new window well needs full excavation or just an upgrade to an existing one.
If the suite has two or three bedrooms, this cost multiplies per window that needs correction. It's one of the reasons a suite conversion quote can move meaningfully once we've actually measured every proposed bedroom window rather than assumed the existing openings are close enough. A full breakdown of cutting a new opening, including the drainage tie-in, is on our egress window cost page.
Sill height: the detail that changes the budget
Clear opening size isn't the only thing that decides whether an egress window passes. The window also has to sit low enough on the wall for someone to actually reach and climb through it. On a lot of North Shore houses the existing sill sits above the top of the foundation footing, which means getting a compliant window in means underpinning and extending the foundation down before the new opening can even be cut.
This is the detail that explains why two nearly identical suite conversions on the same street can land far apart in price. We've quoted the same size of window swap on two houses a few doors apart and landed $5,000 apart, because one foundation was poured several inches higher than the other. Sill height is why we measure the actual foundation on site rather than pricing off a floor plan.
How egress ties into the fire separation inspection
Egress windows don't get signed off on their own. The building inspector checks them as part of the same visit that reviews fire separation between the suite and the rest of the house, because both requirements exist for the same reason: getting people out safely if there's a fire. A suite with a perfect one-hour fire-rated ceiling assembly still fails inspection if a bedroom window is 50 millimetres short on clear opening.
That sequencing matters for scheduling. Framing the egress opening, pouring or patching the window well, and closing up the fire separation assembly all have to happen before drywall goes up and before the inspector can sign off either item. If you're planning the suite conversion timeline, budget the egress window work into the same phase as the fire separation work, not as a separate later step. Our fire separation guide covers what that assembly has to include.
Which window style actually fits the opening
Once the opening is cut to size, the window style itself matters for whether the clear opening calculation still passes. A casement window, hinged on one side and cranked open, gives close to the full frame size as clear opening because the whole sash swings clear. A slider only opens to half its width, so a slider has to be roughly twice as wide as a casement to deliver the same 0.35 square metre clear opening, which is often the difference between a window that fits the available wall space and one that doesn't.
That's why most egress retrofits on North Shore basements end up as casement units rather than sliders, even where the original opening was a slider. It's not a style preference. A casement gets you to code in a smaller rough opening, which matters when the available wall height between the floor and the ceiling joists is already tight.
What we check before we quote a suite conversion
On every basement suite quote, we measure the actual clear opening of every proposed bedroom window with a tape measure against the wall, not the manufacturer's stated size, before we price anything else. Manufacturer specs describe the frame or the rough opening, not the glass-to-glass clear area a body has to pass through, and the two numbers are rarely the same on a window installed 30 or 40 years ago.
We also check sill height, window well depth and clearance, and whether the existing well has a drain tied into the perimeter system or just fills with water every November. A window that needs a new well but no foundation cutting is a different, cheaper job than one that needs both, and the only way to know which one you have is to measure it before the quote, not after the framing starts.
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Frequently asked questions
What is the minimum size for a secondary suite egress window in BC?
BC Building Code requires a minimum clear opening of 0.35 square metres, with no dimension smaller than 380 millimetres, for a bedroom egress window in a secondary suite. This is measured as the actual openable area, not the window frame size, which is why some original basement windows fail the calculation despite looking adequate.
How much clearance does a window well need in front of an egress window?
BC code requires at least 760 millimetres of clearance in front of an egress window that opens into a below-grade window well, giving enough room for a person to climb out during an emergency. Many older North Shore basements need a new or enlarged window well installed to meet this.
Can an egress window have security bars?
Yes, but the bars or grille need a release mechanism operable from inside the room without a key or tool. A fixed grille bolted from the outside does not meet code, regardless of how large the underlying window opening is. The inspector checks the release mechanism by operating it during the final inspection, not just by measuring the window, so a bar system installed without one fails inspection even if the window itself passes.
How much does it cost to enlarge a basement window for egress?
Enlarging an existing basement window opening to meet egress size, including cutting the foundation wall, installing a larger window unit, and building a code-compliant window well, typically runs $3,500 to $8,000 per window. Cost depends on foundation material and whether a new window well needs full excavation.
Does every bedroom in a secondary suite need its own egress window?
Yes. BC Building Code requires each bedroom in a secondary suite to have its own egress window or exterior door meeting the minimum size and operation rules. A two- or three-bedroom suite with undersized original windows in each room multiplies the correction cost per bedroom.
Does an egress window need a screen?
A screen can be present, but it must not need to be removed before the window can be opened for escape. Any hardware between the interior of the room and the outside opening has to release without tools, which affects how screens and security grilles are specified on a suite window.
Is an exterior door an acceptable substitute for an egress window?
Yes. BC Building Code allows either a window or an exterior door opening directly from the bedroom to satisfy egress, as long as it opens from the inside without keys or tools. This is more common in suite bedrooms near a walk-out grade than in fully below-grade rooms.
Who checks egress windows during a secondary suite inspection?
The municipal building inspector checks egress window size, window well clearance, and operability as part of the final inspection for a secondary suite permit in North Vancouver. This is measured on site with a tape measure against the specific BC Building Code dimensions, not assessed by appearance.
Is a casement window better than a slider for meeting egress?
A casement window opens close to its full frame size, so it reaches the required 0.35 square metre clear opening in a smaller rough opening than a slider needs, since a slider only opens to half its width. On North Shore basements where wall height between the floor and the ceiling joists is limited, a casement is usually the style that fits the available space and still passes.
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