To avoid losing Paradise Lost, Harvard is repairing the leaky roof of Houghton Library.

The project, which began last month, is not an emergency repair. No books in the 42-year-old library have been damaged, said Associate Librarian Roger E. Stoddard.

"In 40 years, you need to renew a roof," he said, adding that "we've had water leaking in the attic."

Houghton, connected to Widener by a second-story overground bridge, contains most of Harvard's rare books, including first editions of Milton and original manuscripts of Hawthorne, said Associate Librarian Roger E. Stoddard.

Stoddard compared the roof reconstruction to Widener's window repairs; neither is an emergency but both are due. He added that this is the first time that the library, built in 1942, has been repaired.

Earlier this fall, Harvard's Construction Management contracted the renovation to Woburn Oak Roofing, which has worked on other Harvard jobs, Stoddard said.

The crew is reinforcing the tarry layer underneath the slate shingles and is replacing worn-down bricks. It is also waterproofing the molding at the roof's edge, said Stoddard.

Project Manager Croliss Van Horn was unavailable for comment on the project's cost.

Houghton has acquired a diverse collection of rare books, all of them gifts. "A lot of papers and honors theses have to be independent work...there's a lot of subjects in which you have to include rare books," said Stoddard.

The library's stacks include first edition of Dan Quixote and Homer's, as well as Audubon's original bird illustrations.

Said Library Assistant James J. Lewis, "It's an important library to have the roof on."