Foam board over old 4in thick fiber board roofing panels
Our neighbor lost his roof in a tornado last week and we are trying to come up with a new roof system with additional insulation properties. This is an older home with 2ft x 8ft x 4in tongue and groove fiber board roofing panels nailed directly to the interior exposed beams. These are structural panels and the beam widths are 4ft. Roof pitch is approximately 4-12. After the storm, all that is left is the roofing panels and the roof is currently tarped for protection. We are contemplating adding some type of foam board, then OSB (or Advantek), then felt and shingles. The foam board is to increase the R-value of the roof. Our concerns are 1) fastening anything to the old fiber board since conventional fasteners tend to pull out, 2) trapping moisture that could eventually reach the fiber board. Your thoughts are appreciated.