Ontario Building Code (Table 9.10.15.4) limits how much of your wall can be windows, based on how close your house is to the property line. Enter your numbers below.
How to measure your limiting distance
Measure from the outside face of your wall to the nearest of these three reference lines — at right angles to your wall.
A — Facing a street
Measure to the centerline of the street — not your front property line. This gives you significantly more distance (and more window area) than you might expect.
B — Neighbour on separate lot
Measure to your property line. Your site plan or a survey shows the exact location. When unsure, use a shorter (conservative) distance.
C — Two buildings, same lot
Measure to the halfway point between the exterior faces of the two buildings.
Step 1
Measure from the outside face of your wall — see diagram above for the 3 scenarios.
Called the "Limiting Distance" in the Ontario Building Code.
⚠️ Front wall facing a street?
Measure to the centerline of the street — not the property line. You get much more distance this way.
💡 Don't know the exact property line?
Use your site plan or a survey. When in doubt, measure conservatively (shorter distance).
Step 2
The full wall area — windows, doors, and solid sections combined — on the side facing the property line. Called the "Exposing Building Face Area."
Ontario Building Code Section 9.10.15 limits the area of unprotected openings — windows, glass doors, and skylights — on walls facing a property line. The closer your house is to the property line, the fewer windows you can have on that wall. This rule exists to limit the spread of fire between buildings.
The Limiting Distance is measured from the outside face of your wall to the nearest property line, or to the centreline of a public way (street, lane), or to an imaginary line halfway between your building and a neighbouring building on the same property.
The Exposing Building Face Area is the total area of the exterior wall on that side — measured from grade to the underside of the floor above (or to the top of the wall for single-storey buildings), and from interior face to interior face of adjacent fire separations.
If your house is more than 3 metres from the property line, you typically have room for a generous amount of glazing. At 6 metres or more, many wall configurations allow 100% glazing.
Found this useful? Support our free tools.