Cellar windows are the small windows set low in a foundation wall to bring daylight, fresh air and, where a room is used as a bedroom, a safe exit into a basement. In Ontario homes they most often take the form of a hopper or slider, sized and placed to meet local building code, and they matter for comfort, resale value and safety alike.
Key Takeaways
- Cellar windows and basement windows are the same thing. Cellar is the older, more British term for the below-grade room.
- A basement bedroom needs an egress window with a clear opening of at least 0.35 square metres and no dimension smaller than 380 millimetres, under the Ontario Building Code.
- Hopper windows are the most common cellar window style in the GTA because they hinge at the bottom and tilt inward for ventilation without taking up wall space.
- Triple-glazed vinyl units cut heat loss far more than older single-pane basement windows and help block draughts at floor level.
- A professional cut-out is often needed to fit a larger egress-sized window into an existing foundation opening.
What Are Cellar Windows?
Cellar windows are the windows fitted into a basement’s foundation wall, usually set close to grade level and smaller than the windows upstairs. They let daylight and air into what would otherwise be a dark space, and in a basement used for living or sleeping, they often double as an emergency exit.
The word cellar is simply an older name for a basement, common in older Ontario housing stock and in British usage. Builders, code documents and window suppliers use basement window and cellar window interchangeably, so you will see both terms on the same product page. In a GTA home, a cellar window is most often a hopper style: hinged at the bottom, tilting inward from the top for airflow, and set into a compact opening a couple of feet above the foundation footing. Larger openings are used where the basement holds a bedroom or a rec room that needs more light. If you are weighing a basement hopper against other below-grade options, our guide to basement hopper windows covers sizing and installation in more detail.
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Do Cellar Windows Need to Meet Egress Rules?
A cellar window only has to meet egress rules if the room behind it is used as a bedroom. Under the Ontario Building Code, a basement bedroom needs a window with an unobstructed opening of at least 0.35 square metres, with neither side under 380 millimetres, and a sill no higher than 1,000 millimetres above the floor.
Egress means a safe way out in a fire or other emergency, and the code treats a below-grade bedroom the same as any other sleeping space in this respect. The window also has to open from the inside without tools, so a hopper or slider that only cranks part way open won’t pass. If your basement is a laundry room, cold cellar or storage area with no bed in it, a smaller, non-egress window is fine. Once you add a bedroom, a home office someone sleeps in occasionally, or convert a basement into a legal secondary suite, the egress rule applies and the opening usually has to grow, which often means cutting the foundation wall wider before the new unit goes in. Our guide on whether a casement window can serve as an egress window explains how other window styles compare for meeting the same rule.
“Most callouts we get for basement bedrooms aren’t about the glass at all, they’re about the opening being too small for the code,” says a lead installation manager at TotalSeal. “We measure the wall first, then talk about window styles, because the size decides more than the style does.”
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How Do Cellar Windows Perform in Canadian Winters?
Cellar windows sit close to grade, where cold ground and snow load make heat loss worse than at a typical wall opening upstairs. A well-built vinyl cellar window with multi-chamber framing, Low-E glass and argon gas fill keeps that heat loss in check and cuts draughts at floor level, where cold air pools first.
Triple glazing reaches U-factors of roughly 1.0 to 1.3 W/m²K, against about 1.6 to 1.9 W/m²K for typical double glazing, a meaningful gap given how much time cold basement air spends against the glass. Warm-edge hybrid spacers, rather than older aluminium spacers, improve condensation resistance by up to about 25%, which matters in a basement where humidity already runs higher. Look for windows carrying ENERGY STAR™ certification for the Ontario climate zone; that certification confirms independent testing against Canadian winter conditions rather than a manufacturer’s own claim, per Natural Resources Canada’s energy efficiency programme. Argon fills add roughly another 25 to 30% to glazing efficiency on top of the coating and spacer gains.
“A cellar window has a rough time of it. It’s near the ground, it’s often below the frost line on one side, and it takes the brunt of snow melt and splashback,” says a senior product engineer at TotalSeal. “We build these with the same multi-chamber frame and warm-edge spacer as our upper-floor windows, because cutting corners at grade level is where condensation and draughts start.”
Frame Materials and Options Compared
| Material | Insulation | Maintenance | Typical lifespan | Relative cost |
| Vinyl (uPVC) | Very good, multi-chamber options | Low, no painting needed | 25 to 30+ years | Low to moderate |
| Wood | Good, but prone to moisture damage below grade | High, needs regular sealing | 15 to 20 years near grade | High |
| Fibreglass | Very good, stable in temperature swings | Low | 25 to 35 years | High |
| Aluminium | Poor without a thermal break | Low | 20 to 25 years | Moderate |
Vinyl suits a cellar window opening particularly well because it does not rot when splashed by rain or snowmelt the way wood can, and it will not corrode the way bare aluminium does at ground level. Fibreglass performs similarly but usually costs more for a comparable frame depth, which matters less on a small basement opening than it does on a large picture window upstairs.
Glazing and Glass Options
Double glazing pairs two panes of glass with a gas-filled gap between them, while triple glazing adds a third pane and a second gap for extra insulation and quieter rooms. A Low-E coating is a microscopically thin metallic layer on the glass that reflects heat back indoors in winter, and an argon gas fill between panes slows heat transfer compared with plain air.
For a basement, triple glazing is worth the roughly 20 to 30% cost premium in most cases, since the room already runs cooler and any weak point in the glazing shows up as condensation on the frame or sill first. An optional interior i89 coating can reduce heat loss by an estimated 10 to 15% again, useful in a finished basement bedroom where comfort matters as much as it does upstairs.
Pros of triple glazing in a basement:
- Lower U-factor means less heat escapes through the glass in winter
- Extra pane cuts outside noise, useful near a busy street or laneway
- Warmer interior glass surface reduces condensation risk
Cons of triple glazing in a basement:
- Higher upfront cost than double glazing
- Slightly heavier sash, which matters more on a hopper that tilts open
Pros and Cons of Cellar Windows
Pros:
- Bring natural daylight into an otherwise dark room
- Improve airflow and reduce musty odours common in basements
- Can satisfy egress code, letting you legally use the space as a bedroom
- Add resale value when a basement is finished and code-compliant
- Vinyl frames resist moisture better than wood at grade level
Cons:
- Smaller openings limit how much daylight a single window can add
- Meeting egress size may require cutting the foundation wall, adding cost
- Window wells need regular clearing of leaves and snow to stay effective
Which Homes and Rooms Suit Cellar Windows?
Cellar windows suit almost any Ontario home with a basement, but the right size and style depend on how the room is used. A cold cellar or storage room can keep a small hopper window, while a finished basement bedroom, rental suite or home gym benefits from a larger, code-compliant opening.
In a detached or semi-detached home, a basement apartment intended for rental income needs at least one egress-sized window per bedroom, since a secondary suite is inspected against the same fire safety rules as the rest of the house. In a townhouse, window wells often sit closer to a shared property line, so check clearance before enlarging an opening. Condos rarely have this issue since basements are uncommon in that housing type. If you are planning a basement renovation, our piece on reducing heat loss in winter is a useful companion read before you finalise window choices.
What Do Cellar Windows Cost in the GTA?
| Configuration | Typical price range (CAD, supplied and installed) |
| Small hopper, non-egress, standard opening | $500 to $900 |
| Egress-sized hopper, existing opening | $700 to $1,200 |
| Egress-sized hopper with foundation cut-out | $1,500 to $3,000+ |
| Basement slider window | $600 to $1,100 |
Prices move with glass package, frame depth and whether the foundation opening needs to be enlarged. A straightforward swap into an existing opening costs far less than a cut-out job, since cutting concrete or block, adding a window well and finishing the interior all add labour. Our cost estimator gives a ballpark figure for your specific project before you book a visit, and if the opening needs enlarging, our window cut-out services page explains what that work involves.
“Homeowners are often surprised the window itself is the smaller part of the bill on a cut-out job,” says a lead installation manager at TotalSeal. “Cutting the foundation, adding a proper window well and making sure water drains away from the house is where most of the labour goes.”
How to Choose and Buy
Start by measuring the existing rough opening width and height, and note the sill height above the interior floor. If the room is or will become a bedroom, compare that measurement against the 0.35 square metre and 380 millimetre minimums before you shop, since a smaller opening will need enlarging.
Ask any installer whether the quote includes the window well, interior trim and any foundation cutting, since these are easy to leave out of a bare unit price. A free in-home consultation lets a professional confirm the opening size, check for moisture or settling issues around the foundation, and recommend a frame depth that fits your wall thickness. Book a free quote and consultation to get exact numbers for your home rather than working from a general price range.
Frequently Asked Questions
What is the minimum size for a basement egress window in Ontario?
The Ontario Building Code requires an unobstructed opening of at least 0.35 square metres, with no dimension under 380 millimetres, and a sill no higher than 1,000 millimetres above the floor.
Is a cellar window the same as a basement window?
Yes. Cellar and basement mean the same below-grade room, so cellar window and basement window describe the same product.
Can a hopper window be used as an egress window?
Yes, as long as the clear opening meets the minimum size and the window opens from the inside without tools once installed.
How much does it cost to enlarge a basement window opening?
Cutting a foundation wall wider for an egress-sized window typically adds $800 to $2,000 or more to the job, depending on wall thickness and material.
Do cellar windows need a window well?
Most below-grade windows need a window well to hold back soil, allow the sash to open and let daylight reach the glass, along with drainage to stop water pooling against the foundation.
What glass is best for a basement window?
Triple glazing with a Low-E coating and argon fill performs best in a basement, where cold ground and higher humidity make heat loss and condensation more likely.
Do basement windows need a permit in Ontario?
Enlarging a foundation opening for a new or bigger basement window generally needs a building permit, since it involves structural work; check with your local municipality before starting.
Ready to Upgrade Your Cellar Windows?
Whether you need a straightforward hopper swap or a full egress-sized cut-out for a basement bedroom, getting the sizing and glazing right the first time saves money and headaches later. Book a free, no-obligation consultation through our cost estimator and get an accurate picture of what your basement project will cost before you commit.
