Purpose Life cycle assessment (LCA) has not been widely applied in the building design process because it is perceived to be complex and time-consuming. There is a high demand for simplified approaches that architects can use without detailed knowledge of LCA. This paper presents a parametric LCA approach, which allows architects to efficiently reduce the environmental impact of building designs. Methods First, the requirements for design-integrated LCA are analyzed. Then, assumptions to simplify the required data input are made and a parametric model is established. The model parametrizes all input, including building geometry, materials, and boundary conditions, and calculates the LCA in real time. The parametric approach possesses the advantage that input parameters can be adjusted easily and quickly. The architect has two options to improve the design: either through manually changing geometry, building materials, and building services, or through the use of an optimization solver. The parametric model was implemented in a parametric design software and applied using two cases: (a) the design of a new multi-residential building, and (b) retrofitting of a single-family house. Results and discussion We have successfully demonstrated the capability of the approach to find a solution with minimum environmental impact for both examples. In the first example, the parametric method is used to manually compare geometric design variants. The LCA is calculated based on assumptions for materials and building services. In the second example, evolutionary algorithms are employed to find the optimum combination of insulation material, heating system, and windows for retrofitting. We find that there is not one optimum insulation thickness, but many optima, depending on the individual boundary conditions and the chosen environmental indicator. Conclusions By incorporating a simplified LCA into the design process, the additional effort of performing LCA is minimized. The parametric approach allows the architect to focus on his main task of designing the building and finally makes LCA practically useful for design optimization. In the future, further performance analysis capabilities such as life cycle costing can also be integrated.