For the simplest sunroom, such as enclosing an existing porch with a screen enclosure, the typical starting cost averages around $25,000. This type of sunroom involves screens but no glass windows, no special flooring tiles, no insulation and no real protection from outdoor temperatures. These sunrooms provide homeowners with a fun space where they can have birthday parties, talk to friends or enjoy a cold drink on a hot summer day. However, the most basic screen porch additions often add little monetary value to the home.