With the information given it would be difficult for someone to answer this question. More information about the loft and roof above are needed. May a recommend that you consult a local engineer? That is the best way with such things.
Thaddeus "Ted" J. Ryan Putnam Collins Scott Associates tryan@pcsainc.com (253) 383-2797 (253) 383-1557 (fax) www.pcsainc.com