How big must a basement bedroom window be under the Ontario code?

There are minimums for the unobstructed area and for each side of the opening, measured with the sash fully open, and the window must open from inside without keys or tools. The City checks your design against the current code during the permit review, so confirm the figures with the pro.

Is a City permit needed to cut a bigger basement window opening?

Yes. The City of Mississauga lists a new window, or making one bigger, as permit work; a same-size replacement isn't. Zoning rules apply either way, and in Meadowvale Village a bigger opening also needs a Heritage Property Permit. Agree who will prepare and submit the application before work starts.

Does an egress window need a window well?

If the bottom of the window sits below the ground outside, yes. The well holds back the soil and, for a bedroom window, leaves clear space in front so someone can climb out; the code sets a minimum. A good well drains at the bottom and has a cover that opens easily from inside.

Why is my window well filling with water?

Usually because water can't leave it. The drain may be clogged with leaves or silt, or missing. Soil sloping toward the house or a nearby downspout adds more. Clear the well, and if water gets in around the frame, have a pro check the seal and flashing.

Can a basement window's glass be replaced on its own?

Often, yes. When the frame is solid and the problem is only fogged or cracked glass, a pro can have new glass made for the existing frame. If the frame is rotted, or you want a bigger opening anyway, price a new window too. Our broken glass page covers cracked panes.

Basement windows · Mississauga

Bigger basement windows: size rules, permits and keeping water out

Swapping a basement window for one the same size is ordinary window work. Cutting a bigger opening for a bedroom is a small construction project: it needs a City permit, a window that meets the code's size rules, and a well that drains. We're a referral service: we pass your details to an independent local pro, and that pro handles the measuring, the quote and the job.

Same-size swaps and new openings
Permits and size rules, plainly
Window wells and drainage checked

Get a free quote 905-967-0060

Gravel lets rain drain out of the well.

Two kinds of job

Same-size basement window swap vs a new or enlarged opening

The question is whether the foundation opening changes. There's no single standard basement size, so the pro measures either way.

Same-size swap

A new window goes into the existing opening. It suits a window that is drafty, rotted or hard to open; see replacement windows. If only the glass is fogged or cracked, the glass alone can often be replaced.

New or enlarged opening

The wall is cut wider or deeper, usually to finish a bedroom. It comes up often in newer houses such as those in Churchill Meadows. It needs a permit.

Bedroom rules

Egress size rules for bedrooms

Under Ontario's building code, a bedroom with no exterior door needs a window someone can escape through. The code fixes minimums for the unobstructed opening's area and for each side of it, and the window must open from inside without tools or special knowledge. The 2024 Ontario Building Code is the current edition, and the City checks your design against it at permit time.

What counts is the clear opening with the window fully open. Sashes, operator arms and slider panels all reduce it.

Permits

Permits and zoning in Mississauga

An enlarged basement window is permit work here. The usual order:

Settle the design
The pro checks the wall and grade and suggests a window that meets the bedroom rules.
Apply for the permit
The City's permit page lists a new or bigger window as permit work, and notes that zoning rules apply even without a permit. Agree who prepares the application before you sign. In Meadowvale Village, a bigger opening also needs a Heritage Property Permit; see the heritage village guide.
Build and inspect
The opening is cut, the window and well go in, and the work is inspected. Keep the records.

Water

Window wells, drainage and heavy-rain events

Here the weather worry is water, not hail. The summer of 2024 brought two record-setting rainstorms and flooded basements across the city, and the City is running a basement water infiltration investigation in Lisgar. A deeper window puts more of the opening below grade, so the well matters as much as the window. A pro can show where water gets in; nobody can promise a dry basement in every storm.

Drainage at the bottom

Gravel over a drain lets water leave the well, if it isn't clogged.

Grade and downspouts

Soil sloping toward the house or a downspout near the well sends water straight in.

The seal around the frame

Caulking and flashing keep water out of the wall itself.

A cover

Keeps out leaves and some rain. For a bedroom, pick one that opens easily from inside.

Window types

Choosing the window: sliders, casements, awnings

Sliders

No crank to wear out, but only half the width opens, so it needs a larger frame.

Casements

Opens close to full width, but needs room in the well to swing. See casement windows.

Awnings

Good for light and air, usually too small for a bedroom exit. See awning windows.

Price factors

What affects the price of an egress project

How much the opening grows, and whether the wall is poured concrete or block
Window type, size and glass
The well: size, drainage and cover
Digging, equipment access and landscape repair
Interior finishing and permit drawings

Tell us the room, the current window size and whether you're finishing the basement.

Get a basement window quote

Free quotes from independent local pros.

Questions

Basement window questions

Explore your options

Basement window work comes up across the city, including Churchill Meadows, Applewood, Erin Mills and Clarkson & Lorne Park.

Tell us about the room and the window

Say which room it is, the current window size and whether you're finishing the basement. We'll pass it to an independent local pro who does basement windows and wells, and they'll tell you whether it's a same-size swap or permit work.