This is a tricky area and should be approach cautiously. While some of the above stats make sense in some areas, equally as true that your expense to value adding ratio may change significantly by region. Where as taking a 4 bedroom house in one area and re-configuring into a 3 bedroom house allowing for a larger common area floor plan may be a very profitable resale feature somewhere like the Hollywood Hills, but it may actually decrease value if done in a heavy family oriented neighborhood where bedroom count reigns supreme. And where as a wood deck addition would ad value to a sloped lot with a view, could be a waste of money on a flat lot with no view. Every improvement must be looked for optimum use regionally.