In the framework of the German LEGOE project, an integrated tool is developed for computer aided architectural design (CAAD), quantity surveying (catalogue of building elements), life cycle cost calculation and estimation (construction and refurbishment), direct energy consumption (heating, hot-water, electri-city) and environmental impact assessment (mass flows and effect oriented evaluation). During the design process the architect works in his usual CAAD environment with building elements (e.g. one m2 of outer wall) which in turn are composed of detailed construction specifications, energy and mass flow coefficients and cost data. These elements are part of an independent catalogue of elements with all their relevant data. The different application programs use the same basic data and write the specific results into a project-specific database called a PDB which allows the comparison of these data to reference data from other projects. Evaluation and visualisation programs refer to the PDB only.