DENVER (Jan. 31)—Berkshire Hathaway Inc. has extended its tender offer for shares of Denver-based roofing and building products manufacturer Johns Manville Corp. to Feb. 14. The offer, the major component of the $2.2 billion merger agreement between the two firms, was to expire Jan. 29, but not all necessary clearances had been obtained or waiting periods expired under antitrust laws, the companies said. Omaha, Neb.-based Berkshire, through its newly formed subsidiary J Acquisition Corp., is offering $13 per share for outstanding shares of Johns Manville stock. Nearly 87 percent of Johns Manville outstanding shares were validly tendered as a result of the offer, according to the latest count of tendered shares, the firms said. The tender offer was originally filed with the Securities & Exchange Commission on Dec. 29.