Mark Hall has developed special interest and expertise in historic preservation and adaptive reuse of historic structures and city districts. He has served as president of the Los Angeles Conservancy, and designed projects combining historic preservation and appropriate adaptive reuse of the properties. He is a member of the Canadian Association of Heritage Professionals. Recently he served as preservation architect on renovations of the RC Harris Water Plan, a designated cultural heritage building in Toronto. He has served as architect for restoration and additions to a number of historic houses in the Annex, Beaches and other areas of central city Toronto, as well as Belleville, Orillia, Mississauga and Brampton, and in Los Angeles and Florida. He frequently works with property developers as consultant regarding historic properties of concern to municipalities in which they are working.