Complexity and multi-disciplinary represent the challenge that the design and construction of sustainable buildings have to face. The nature and quantity of information needed are further considerations which lead to re-thinking the whole design process. The architect alone cannot have all the skills required, so he/she should be able to rely on other specialized professionals. In some European countries, environmental consultancy-which deals with ecology matters-is becoming more and more crucial for the design of a successful building. Taking into account two British consultancy companies-investigated as case studies-this paper looks at the way the design process related to complex projects is managed, and at the effects on the architectural sector.