The short answer is no, you cannot add windows to the side elevations of a house on a zero lot line lot. The distance between houses is 5’ (instead of 8’ like on a regular lot) and the building code rules require a higher fire protection rating when the buildings are closer together.

The fire protection rating required cannot be attained with a regular window. A 45-minute fire-protected door with no windows is allowed on the easement side of a zero lot line as you can access it without going onto someone else’s property. A door on the property line side of the home, however, isn’t allowed because you would have to go onto the neighbour’s property to use the door.