When architect Paul Bernier and lawyer Joëlle Thibault sought to expand their home in the Plateau Mont-Royal neighborhood of Montreal, they designed two additions: a new office on the top level and a backyard playroom with a green roof. The single-story addition to the row house adds square footage without eating up too much outdoor space. The green roof also helps makes up for lost garden beds, while creating attractive, leafy views from the second and third floors.