In 2005 the Danish Building regulations introduced two low energy classes for buildings in addition to revised minimum requirements. The low energy class 1 and low energy class 2 correspond to total energy use, i.e. energy use for heating, ventilation, cooling and domestic hot water, as 50% and 75% of the minimum requirement respectively. The main purpose of introducing the low energy classes were to further support and encourage the development of low energy buildings. In 2010 it is expected that demands in the Building Regulations are tightened by 25-30% and in 2015 it is expected that the minimum demand will correspond to the low energy class 1 demands of today. In order to secure this development in the demands, it is essential to demonstrate that the goal is well within reach of the Danish building industry. This paper describes the development of a low energy class 1 type house. The house is based on a standard type house, and through an optimisation process of the building constructions and heating and ventilation systems, the total energy consumption for the type house has been reduced in order to meet the low energy class 1 demands. The paper describes the development of the house along with detailed calculations of the energy consumption and indoor climate.