The rule, in the City's own words
You don't have to take my word for any of this. The City of Calgary publishes it on its home renovations page:
City of Calgary
“If you are replacing windows without changing the size of the opening or type/operation of the window, then no permit is required.”
The other half of the rule is just as short: adding new windows or enlarging existing ones does require a building permit. That's the whole framework for a residential window project. No form, no fee, no waiting — as long as you stay inside both conditions.
I'd rather you hear that from me than pay someone to tell you the same thing.
The condition people skim past: “type/operation”
Almost everyone reads same size and stops there. The sentence names a second condition, sitting right next to the first one.
Type and operation mean how the window opens. A slider slides sideways. A casement cranks outward. A tilt-and-turn does two different things on one handle. If the new window opens differently from the old one, the operation has changed. Even when the hole in your wall is identical to the millimetre.
Here's the part that costs me money to write. The windows I install are tilt-and-turn. If yours is a slider today, then on the plain reading of the City's own sentence, that's a change of operation. I'm not going to tell you it doesn't count just because counting it is inconvenient for my quote.
Call the City, describe your exact window, get the answer for your project. It costs ten minutes and nothing else. And it's your name on the house, not mine.
When you definitely need a permit
| Your project | Building permit? | Why |
|---|---|---|
| Same opening, same way it opens | No | The case the City's sentence describes. Nothing structural changes, and nothing about the window changes except its age. |
| Same opening, different operation (slider → casement, casement → tilt-and-turn) | Confirm with the City | Type and operation are named as a separate condition. Don't assume the size clause covers you. |
| Enlarging an existing opening | Yes | Enlarging changes what carries the load above the window. Precisely what the permit process exists to look at. |
| New window where there was solid wall | Yes | A new opening in an exterior wall, by the City's wording. |
| New opening cut into a concrete foundation | Yes — plus engineering | The City requires a professional Engineer's structural review once the width of a new opening exceeds 1.2 m (4'-0"). |
| Any window in a bedroom | Follows the rows above | The permit answer doesn't change, but egress rules apply on their own. See below. |
One honest caveat. The City reads these rules against a specific project, and published guidance is guidance, not a ruling on your house. If your job sits near a line, phone them. They answer.
Bedrooms have a rule that does not care about your permit
If the window is in a bedroom, egress requirements in the National Building Code (Alberta Edition) must be met. Egress means a person can get out of that room through the window, and someone in full gear can get in.
This matters more than the permit question and gets a fraction of the attention. A permit is paperwork. Egress is the window you climb out of at three in the morning.
So when you're replacing a bedroom window, ask whoever is quoting you to state it on the quote, in writing: does the unit meet egress for that room. If the answer turns vague, you've learned something useful about them. And it cost you nothing.
One note on the windows I work with, because it's relevant here and not a pitch. The turn function swings the whole sash inward, like a door. The clear opening is the whole frame, not half of it. Whether that satisfies egress for your room is the City's call, not mine.
What “no permit required” actually means for your project
Here is the consequence nobody puts on a window company's website.
A permit is the mechanism that puts a City file on your project. No permit means no file, and no external checkpoint. Nobody is coming to confirm the window was set plumb. Or that the gap around it was sealed properly. Or that the flashing sends water back out of the wall instead of into it.
Which means the quality of that install rests entirely on whoever you hire. That's not a scare line. It's arithmetic.
The part worth sitting with
The absence of a permit is not a standard. It only means nobody is coming to look. Worth thinking about before you choose who does the work — not after.
It's also why I keep saying the install matters more than the sticker on the glass. A very good window set badly will disappoint you every February. No paperwork anywhere will have flagged it.
So what does this mean for your project?
If you're swapping windows into the same openings and keeping the same operation, get on with it. There's no permit standing between you and a warmer house.
Changing how the windows open, making an opening bigger, cutting into a foundation — budget time for the permit. And for engineering, if a foundation is involved. That time is real. Finding out about it after the order is placed is the expensive way.
And either way: spend the energy you saved on the permit question on the one that actually decides the outcome. Who is setting the window, and how.