The company began as the multi-disciplined partnership of Rainey Petrie Design in 1990, and expanded through the 1990s with the inclusion of Graham Johns Associates in 1995 to form the company Rainey Petrie Johns Ltd.  As well as continuing its design emphasis it also developed as a specialist building technical consultancy to respond to the rapid growth in the differing ways of procurement and the constant shift of the legislative framework, particularly in the public sector in provision of schools, courts and other public buildings. On the retirement of Graham Johns the practice operated as RP Design Consultants Ltd.

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In 2008 Rainey Petrie Architecture Ltd was established as a sister company of Christopher Scott Ltd and in 2019 began operation as Rainey Petrie Architecture (a brand of ERMC Ltd), and as a Chartered Architectural Practice continues to provide a quality and innovative design and technical service to its existing and new client base.