ElkCorp ( ELK), a maker of roofing and building products, said its board recommended that shareholders turn down the $40-a-share cash takeover offer from Building Materials Corp. of America. The board believes the tender offer is excessively conditional, lacks appropriate financing and is "potentially illusory." ElkCorp agreed last month to be acquired by the Carlyle Group for $38 a share. However, the company said it's holding active negotiations with Building Materials and its affiliate, Samuel Heyman, "to develop a transaction that would merit recommendation to ElkCorp's shareholders." The board continues to support the Carlyle transaction at this time. ElkCorp closed Monday at $40.63.