I have a Calf. ranch home with a vaulted ceiling, problem is roof line is sagging !!! This problem can not be seen inside just outside. Roof is 28yrs old and yes it does need replacing, but how do I get the sag out ?? Span of roof is 20' made of 2 X 4's with no inside support. Thinkg about replacing all roof joist with 2 x 6's and hope this will help, but that means removing all drywall inside. If I sandwhich the 2x6's to the 2x4's this would off set my 16oc marks... Any ideas or help??????