In Florence, Modernizing a 15th-Century Palazzo Andrea Wyner for The New York Times The red and black leather seating in the dining area was custom-made by Architema. The Castiglioni Arco lamp ($2,232) and the Le Corbusier table ($4,960) were bought at auction in Milan. FOR Paolo Mazza, the Palazzo Bardi was supposed to be just another project at work. Mr. Mazza, now 59, was the chief executive of Amplifin S.p.A., an investment firm in Milan, in 2000, when his company acquired the property, a 15th-century palazzo said to have been designed by the great Renaissance architect Filippo Brunelleschi. The plan was to convert it into apartments to sell, and for the next several years Mr. Mazza supervised the architects charged with the delicate task of carving up the building. One space had the distinction of being a theater that was a meeting place for the Florentine Camerata, the group of 16th-century musicians and theorists credited with inventing opera. "When I saw the architects" plans to carve up the theater, which in its original form was as open and acoustically pristine as a theater ought to be," Mr. Mazza said, "I had to intervene." In 2008, he halted work on La Camerata, as the 3,444-square-foot theater is now known, and bought it himself, for 2.5 million euros (about $3,875,000 at the time). He and his wife, Gabriella, now 56, then put four years of work - and another $1.5 million - into turning it into a home. It was a project that Mrs. Mazza, a former owner of a luxury retirement community, said involved dealing with a lot of red tape because of the theater's historic significance. "We were constantly dovetailing the tiring tasks of wading through a legal swamp of restoration requirements while trying to leave our own interior-design stamp on the property," she said. Working in consultation with artists and historians from the Accademia di Belle Arti, the art academy in Florence, they submitted nearly two dozen architectural proposals and renderings to the Municipality of Florence and to the Italian Ministry of Cultural Heritage, before construction could begin. The space was lofty and open, as befitting a theater, and the Mazzas wanted to keep it that way. So they turned the one private room, a study near the entrance, into a bedroom and bathroom. To preserve the open space's integrity, they inserted a giant free-standing structure, creating two guest rooms with bathrooms on the lower level (for their children, Francesco, 32, and Giulia, 25, who live in Milan) and a modern kitchen, dining and living area above. A marble staircase with a wrought-iron railing leads to the second level, where a glass-and-steel railing stretches the length of the mezzanine, overlooking the open space below. But first, there was a huge amount of restoration to be done. The frescos in what would become the master bedroom needed to be restored, and the wood-beamed ceilings and 12-foot-tall wooden shutters were covered in centuries of paint. So the Mazzas hired Dini Restauri, a restoration company, to strip the space down to its original state. Workers spent seven months picking away at the heavy layers of lead paint on the walls with chisels and hammers, finishing the job with a calcium oxide wash that accentuated the chiseled effect. And the paint on the woodwork was removed to reveal pastel flower stencils on the paneled ceilings. When the Mazzas bought the apartment, they also bought a street-level space in the building that was originally a 15th-century buchetta, the Renaissance equivalent of a fast-food drive-through that sold food staples. Their intention was to turn it into a two-car garage. But like many of their plans, that was vetoed. Authorities deemed the space too historically important to be used for parking. So the couple did what they learned to do during the renovation: they improvised. And now they run a restaurant in that space called La Buchetta.