Standards and regulations can play a central role in policies to achieve environmentally sound and energy-efficient buildings. This paper sets out to explore how consulting engineers relate to standards designed to impose sustainability in the construction of new buildings and in waste management. The paper addresses four cases of engineering practices. The first case describes practical skills and tools involved in what the engineers considered as ‘normal’ practices when performing energy calculations in the development of new buildings. The second and third cases deal with energy in new buildings as well, but address practices that supported or enabled the engineers to go beyond minimum standards. Case four explores a heat production project and more specifically, how the engineer deals with solving a problem related to calculating energy substitution. Together, the cases represent situations with quite different degrees of uncertainty as to how to relate to standards, from relative certainty represented in the first case to relative uncertainty in the last case. We shall look closer at the practices such situations entail and how they constitute different types of consulting engineering practices.