The results of an experimental study examining the steady exchange of air and heat between a building and an urban canyon are presented. The focus is on the effect of the canyon aspect ratio on the airflow through openings made exclusively in one side of the building. The interaction of the external wind flow and the internal thermally-driven flow was shown to depend upon the ratio of the building height Hb to the canyon width W (distance between buildings forming the canyons). The trends observed as this aspect ratio (Hb/W) was varied allow for identification of canyon geometries that yield reduced or enhanced building ventilation airflow rates.