The firm is noted for its prominent role in bringing modern architecture to Alberta.
During World War II the Rule brother's father, also named Peter, took charge of the firm.
In 1945 the firm opened a second office in Calgary which was headed by Peter Rule (son).
Since 1938, the firm has undergone several name and partner changes including Wynn Forbes Lord Architects (Gordon Wynn, Gordon Forbes and George Lord), Wynn Forbes Lord Feldberg Schmidt Architects (Gordon Wynn, Gordon Forbes, George Lord, Heinz Feldberg and Sig Schmidt), Schmidt Feldberg Croll Henderson Architects (Sig Schmidt, Heinz Feldberg, Norm Croll, Craig Henderson and Eric Underwood), Henderson Inglis Architects (Craig Henderson, Stewart Inglis) and HIP Architects (Craig Henderson, Stewart Inglis, Allan Partridge and Randy Krebes).
In 2013, on its 75 year anniversary, Stewart Inglis and Randy Krebes merged the firm with Kasian Architecture, Planning and Interior Design.