The Ainsworth house in St. Louis Park was being slowly consumed by books.

Massive bookshelves covered an entire wall in the living room. Another room upstairs had almost no visible wall space. Nearly every room in the house was outfitted with a bookcase, including the kitchen. Still, Louis Ainsworth's book collection threatened to overrun the property.

"What Louis couldn't fit on the shelves, he kept in cardboard boxes around the house," says Sue Ainsworth, the book collector's ever-patient wife. "I would tell him, 'Louis, why do you need 500 books on the Middle Ages?'"

When the Ainsworths met their breaking point, they did something even bibliophiles might consider drastic: They bought the house next door, added a two-story atrium to bridge the 15-foot gap between the houses, and converted most of the neighbor's house into a two-story library with cherry shelves, a mezzanine, fireplace and a rolling library ladder.

"It's the pièce de résistance of the house," says Sue.

Hanging onto history

At first the Ainsworths thought they would demolish the neighboring house to claim its square footage for the library. (This was 2005, after all, when knocking down a neighbor's house to build a giant house was almost cliche in some circles.) But as they researched, the Ainsworths discovered a kind of odd symbiosis between their house and the one next door.

Both were built by Thorpe Brothers in 1931. Both have simple, boxy shapes, and the same plot lines and square footage. And, aside from the house across the street, they stood alone for more than a decade in what is now a high-density neighborhood just minutes from Excelsior and Grand.

"There were three two-story houses here, in a cluster, in an open prairie, for almost 15 years before the next houses were built in the 1940s," says Sue. "We felt oddly compelled to save this other house."

Still, the Ainsworths were certain the city of St. Louis Park would balk at the idea of conjoining two houses. "St. Louis Park has an ... exacting ... reputation when it comes to building codes," says Louis, who chooses his language like the attorney he is. But when the pair checked with municipal authorities, they discovered that no one in the city's 124-year history had asked to do such a thing, so there were no prohibitions against it.

With all systems go, the Ainsworths reached out to Minneapolis architect Daryl Hansen with their unusual assignment. Hansen let well enough alone in the couple's existing house, save for a kitchen remodeling that added a barrel-vaulted ceiling and arching custom cabinetry for Sue's collection of vintage teapots and teacups.

For the 15-foot gap between the houses, Hansen designed a two-story vaulted atrium with a geometric wrought iron railing inset with three 100-year-old stained glass panels from England. Sue had the room painted a deep, cranberry red and added colorful oil paintings by Maple Grove artist Calvin deRuyter. It now serves at the pair's receiving hall and formal dining room.

Two into one

Blending these two houses wasn't quite the Frankenstein-esque job it could have been. The builder in 1931 used divided-light windows and arched doorways in both houses, so Hansen was able to amplify the similarities. He added arched doorways to the new spaces that line up in parallel formation with the arched doorways already in place. A new sunroom/greenhouse at the back of the atrium is completely surrounded by divided-light windows and French doors, in homage to the windows of the original houses.

But it's the exterior that really pulls the two structures together. Both houses shed their skins in favor of charcoal gray stucco and narrow shutters. A wide porch bolstered by white columns draws a connecting line between the three structures.

"The trick was making the house seem as one, without making it seem so massive," says Hansen. To reduce the scale, Hansen simply set the center atrium about 8 inches below the rooflines of the houses, like a little vaulted cottage wedged between two older siblings.

Inside, guests are immediately taken by the atrium, especially when the stained glass panels throw shards of color around the room at certain times of day. But the library is the main attraction, with its 7,000 volumes stretching right up to the ceiling. Most of Louis' collection deals with ancient history, followed by medieval and then military history, especially World War II. Louis has organized it all by category, and then alphabetized. A potbelly stove rests in the fireplace, and two A. Rudin wingback chairs make up the only furniture.

"I can sit in here for hours," says Louis.

The second level of the library is where smaller collections of foreign language, poetry, science, literature and beach reads reside. Here, too, is Louis' office, where he tracks his collection with a computer database system.

The rest of the neighbor's house, just off the library, includes a dining room and a second kitchen. The Ainsworths have done little to these spaces, but plan to convert the dining room to a playroom when -- and if -- they have grandchildren. They may even consider a lower-level master suite down the road.

But what they won't ever consider is buying a Kindle.

"This," says Sue, "is a strictly text-bound household."

Alyssa Ford is a Minneapolis-based freelance writer.