A British auction house is selling 12 blueprints that show the arrangement of windows at Fallingwater, the summer house Frank Lloyd Wright designed for the Edgar Kaufmann family in Fayette County.

On its website, PFC Auctions states the drawings turned up on Long Island, N.Y., accompanied by a letter from architect Arthur Hennighausen, who was based in Waukegan, Ill., in the spring of 1938. That year, J.D. Graf, a salesman for Hope Windows Inc., gave Hennighausen drawings of the "Falling Water steel sash" as a professional courtesy, according to the letter.

Hennighausen died at age 94 in 2007. Before his death, in 2006, the blueprints were offered at Heritage Auctions in Dallas but did not sell.

Jerry Morosco, a South Side architect who handled thousands of Wright drawings while a Taliesin Fellow from 1981-86, said the documents are shop drawings prepared by Hope, which made the windows, sashes and exterior doors for Fallingwater. The drawings show how Wright eliminated mullions from corner windows. Hope, which is based in Jamestown, N.Y., is still in business and makes the windows visitors see at Fallingwater.

"These drawings were not prepared by Frank Lloyd Wright or at Taliesin," Wright's studio in Spring Green, Wis., Mr. Morosco said. "Not only did they not come from Taliesin, they are copies of original drawings."

"It's very rare that you're going to find original Frank Lloyd Wright drawings," Mr. Morosco said. "The drawings are precursors of that built work and show ideas."

In pencil, someone scribbled "F.L. Wright" on the back of one of the drawings, but Mr. Morosco does not believe the writing is from Wright's hand. On its website, the auction house states that the blueprints show signs of use and wear and acknowledges that it is unknown whether the scrawl was Wright's.

Bidding opened on Sept. 14 and closes at 2 p.m. Thursday. At press time on Tuesday, the highest bid was 14,172 pounds ($22,953).

Asked what he made of that bid, Mr. Morosco replied, "That somebody has a lot of discretionary income and an affliction for things Frank Lloyd Wright."

In June, a blueprint for the back wall of the guest house at Fallingwater, along with an angry letter Wright wrote to builder Walter J. Hall, sold for $27,970 at RR Auction in Amherst, N.H.

Lynda Waggoner, director of Fallingwater, said she and her staff are focused on preserving the house, "not preserving drawings of what's in the house." However, Fallingwater keeps copies of the home's blueprints for scholars to use.

First Published: September 26, 2012, 4:00 a.m.