Many Beijing Siheyuan, a type of Chinese vernacular housing with significant cul-tural value, have been lost in recent years.Preserving the few remaining has become a neces-sity, but many contemporary architects lack an understanding of their design principles.Based on a historical analysis deriving from Fengshui theory, the Gongcheng Zuofa Zeli ancient con-struction manual, and craftsmen's experience, this paper describes a parametric algorithm capable of producing Siheyuan variants within a 4D CAD environment which by transforming the original design principles into an algorithm contributes to an understanding of Siheyuan ty-pology and their preservation.This algorithm was implemented in a virtual scripting environ-ment to generate accurate virtual counterparts of historical or extant Siheyuan houses revealing the tacit computational rules underlying traditional Chinese architecture.