In 2005 the Danish Building regulations introduced two low energy classes for buildings in addition to tightened 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 Denmark. In 2010 it is expected that demands of 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 building regulations, it is essential to support the development of low energy solutions and demonstrate that the goal is well within reach of the Danish building industry. This paper describes the development of a low energy class 1 typehouse. The house is based on a standard typehouse, and through an optimization process of the building constructions and heating and ventilation systems, the total energy use for the typehouse has been reduced in order to meet the low energy class 1 demands. The paper describes the original typehouse solution, optimization process and detailed simulations of the energy use and indoor climate of the optimized solution.