The loft is a two story apartment where the wizarding Russo family lives. It is located above the Waverly Sub Station and the lair.
Features
The loft is a ordinary house, with sofas, washing machines, a dinning table and a counter to make meals. It also has a balcony that allows the Russo family to look at the city. Upstairs are the bedrooms, but they're rarely seen. Max's room is seen in Report Card.
History
Before the series
After Theresa and Jerry married, they bought the apartment where the Russo siblings would grown up. It's possible that they would later add the stairwell into the Sub Station and that at some point the lair had been created, though it's not known who charmed it.
The series
As the Russo spent most of their time in the lair or the sub station, the loft is seen during the Russo free time. It was in the loft that Max gained his full powers (and maybe his siblings also). However, after Alex wrongly fell in love with herself after drink a love potion, Justin gave the hat to neutralize the potions side effects (it made her head grow to epic proportions) Max unstable full powers began to summon food from the four corners of the world.
In season three Mason came to dinner with the Russo but he abruptly left, which made Alex suspicious. It would be in the loft that the Russo would came to known about Mason being a werewolf.