Constructing Energy Efficiency: Rethinking and Redesigning the Architectural Detail

Abstract

Energy-efficient building design, especially in residential construction, strongly relies on thermophysical properties of the building envelope and its materials. With increasing insulation values in construction practice, the focus turns to the prevention of thermal bridging as well as airtight construction to reduce unwanted heat transfer through the envelope. The building envelope serves multiple functions apart from heat retention that are tied to structure, safety, and visual appeal or aesthetics; and the stakeholders in the design and construction process all have different decision criteria. Supported by disciplinary education separating engineering and architecture and based on the dogma of Modern Architecture, most contemporary architects consider slender details and clear separation of architectural elements to be intrinsic to good architectural design thinking. The engineer involved in the design of the HVAC systems considers the envelope as the basis for the load calculation, whereas the construction engineer and project manager prioritize cost, maintenance, and constructability. Tradeoffs have to be considered and possibly a new proportional relationship has to be found for a building envelope between the increased need for insulation, seals and gaskets, structural necessities, and exterior appearance; and ideally without penetrating elements that could conduct heat from hot to cold. Considering current construction techniques, conceptual design thinking, proportional relationships, and building science, this paper analyzes energy efficient envelope construction methods and details strategies of the U.S. DOE 2009 Solar Decathlon homes. The paper will evaluate the influence that envelope construction methods which prevent thermal bridges have on the potential to develop a coherent exterior and interior appearance, thermal performance, and constructability to develop a balance between materials and thermodynamics. Different value systems exist within the design team related to the building envelope and lead to a trade-off pentagram. For architects, the envelope carries aesthetic, symbolic, and sometimes even cultural meaning, while it is just one of many parameters for the load calculation of the HVAC engineer and a means to protect the structural elements of a building and to protect against water and fire for the construction engineer. The paper thus concludes with a design recommendation of how to reduce thermal bridging in the building envelope and still maintain aesthetic values pertinent to architectural pedagogy.