In designing a Passive House, we use software known as PHPP (Passive House Planning Package), an assessment tool to calculate the energy performance, overheating and other environmental issues in the building. Factors such as climate data, building orientation, the use of highly efficient windows and doors, heat recovery ventilation system, solar shading, calculation of U-Values, designing out thermal bridges, air tightness levels, energy efficient boilers, etc., are addressed, input into the software and analysed. Recommendations are made on the results produced. They address cost, buildability, etc. and the best balances considered by a Certified European Passive House Designer and Architect. These results are taken into consideration at planning stage to achieve a dwelling with minimum heat losses and maximum heat gains. Once the project goes to detailed design and construction stage, constant monitoring of the PHPP findings ensures the dwelling remains within the Passive House criteria.