PREVIOUS SPREAD, FROM LEFT: Nearly 2,000 books, curated by bookseller Kinsey Marable, line the shelves of the hand-cerused European white oak-paneled library. Black-and-honey rattan chairs (Paolo Moschino) and "peanut-butter-and-jelly" zellige floor tiles (Mosaic Factory) lend a playful spirit to the breakfast conservatory. BELOW, FROM LEFT: A foliage-laden mudroom hall offers a verdant welcome. Mirror, Michael-Cleary. Andy Warhol's Sitting Bull, a nod to the homeowner's American Indian heritage, presides over the library's neoclassical cabinet. OPPOSITE: Hammered metal sconces (Soane) ascend the stair hall's botanical de Gournay wallpaper.

Every new house comes with surprises, traditions tweaked, leaps of faith.

In the case of a new suburban residence outside of Chicago, the first twist was the owners' decision to build it at all. They'd initially contacted designer Summer Thornton to help plan an addition to their existing home.

"They wanted to freshen things up," Thornton says of the clients she had worked with on prior projects. However, the addition they had in mind was an ambitious two-story library-something the husband had longed for since childhood.

"It looked odd to tack the library on to the existing house," says architect Heidi Lightner, whose firm was hired to draw up the plan. So she approached theclients with a proposal: "If you really want to do this right," she told them, "you should design a new house around the library." They said, "OK, let's do it!" Yet their lot was fairly small, and they didn't want to move.

The wife had grown up in Chicago, and most of her relatives still live nearby; her twin sister's backyard even abuts hers.

"I have a huge, close-knit family," she says. "Eight siblings, lots of nieces and nephews, three grown kids." Last year for Thanksgiving, she hosted 52 people for dinner.