This paper proposes a method to aid in the comparison and choice of alternatives for assemblies closely related to buildings' thermal performance. The method provides an assessment of the environmental, energy and economic life cycle from cradle-to-cradle (3E-C2C) following recent European Standards for the environmental and economic assessment of construction works. Environmental performance is assessed using life cycle assessment method, energy performance corresponds to consumption of energy for heating and cooling, and the economic performance is based on the whole-life costing (WLC) method. The 3E cost-C2C approach establishes weights that allow the quantification of each aspect of the assembly's performance using the same unit. This approach uses a prevention-based environmental impact assessment method that converts the results of all impact categories into an economic unit. This allows the cost of the environmental impacts to be added to the economic and energy WLC and a 3E performance C2C to be considered, therefore preventing contradictory conclusions that can arise from the individual analysis of each aspect. 3E-C2C is useful in the selection of an external wall alternative, and corresponding insulation thickness, when comparing alternatives that are not functionally equivalent, since there is no need to change their characteristics to make them comparable. (C) 2013 Elsevier B.V. All rights reserved.