The fire was reported shortly before 7 a.m. and flames were out just over an hour later. The northwest corner of the house was extensively damaged, authorities said.
``Right now we're treating it as a suspicious fire,'' said Norwalk Fire Chief Tom Fleming, whose department was among four called to the blaze.
Fire burned through the interior and exterior walls and from the basement up into the attic, he said.
The two-story wood-framed house sits in the countryside 10 miles northwest of Winterset. It is known as ``Francesca's house'' because it was used in the 1995 film as the home of lead character Francesca Johnson, portrayed by Meryl Streep.
The film was based on Robert Waller's 1992 best-selling novel that featured central Iowa's covered bridges as the focal point for a romantic relationship between Johnson and professional photographer Robert Kincaid.
Clint Eastwood produced, directed and starred in the film.
One of the covered bridges featured in the novel and film was destroyed in 2002. Another bridge was damaged last month.
Madison County Sheriff Paul Welch said the timing of the fire days before the annual Madison County Covered Bridge Festival, heightens his concern that the tourist attractions are being targeted.
``It's very unfortunate and I suppose you could use that as an indicator, with the festival coming up and this is part of the scenario also,'' Welch said. ``This is all part of the movie and it's very concerning,'' Welch said.
Inside the home, a gift shop selling movie memorabilia had smoke damage. The house remains decorated with many of the movie props used in filming.
``I couldn't believe somebody has done something like this again,'' said Barb Bell, who owns the farmhouse. ``It's a hard day.''
The house had been abandoned for nearly 35 years but was renovated for the movie.
Welch said no leads have developed in the arson fires that damaged two of the bridges featured in the novel.
``I think it's causing quite a bit of concern around here. It's something that can't be replaced,'' said Ron Waugh, who lives a mile east of the house. ``I just don't understand why people have to destroy something like that.''
Madison County once had 19 covered bridges; five remain standing. All are listed on the National Register of Historic Places. The covered bridge festival, an annual event, is scheduled this weekend.
