Between 1889 and 1909 while he worked at his studio in Oak Park and his office in Chicago, Wright designed more than 150 buildings, which is a huge number for such a short amount of time. He hired draftsmen and architects to work in the studio, assisting with design and construction. Wright was formulating his ideas about a truly American style of architecture, and for the first twenty years of his career he designed buildings in what is now called the Prairie style. It was based on the idea that the design of a building should appear to grow from its site and open up a new world to those who live in it. By combining landscape and lifestyle, Wright created houses that improved the way his clients lived. The floor plans were open and flowing, not boxy and dark. The houses had overhanging roofs to better protect them from bright sun and thunderstorms. There were rows of art glass windows with abstracted designs from nature. They also had huge fireplaces because Wright thought of the hearth as the heart of the home. Wright's clients loved the houses he was building, and that is why he had so many commissions in the first twenty years of his career. But his marriage wasn't very happy, and he left for Europe in 1909 with the wife of a client.