Large commercial roof replacement

The contractor will tear off all roofs down to the structural decking(consists of metal B decking and gypsum decking. The contractor will include replacement of 20% of the gypsum decking and 10% of the steel decking, to be replaced with 20 ga. steel B decking to be spanned a minimum of 2 structural members for bad decking, obsolete equipment, or the removal of old/broken skylights. Over the gypsum decking, contractor will install a smooth 28Ib base sheet, nailed to the gypsum decking with gypsum fasteners that will be fastened at minimum of 8" on center or to warranty requirements set forth by the roofing manufacturer(whichever is more stringent , the sheets will overlap a minimum of 4" and completely cover the entire deck. Areas that have metal decking or new metal decking will not have any base sheet installed over the decking. The contractor will install wood nailer to match the new insulation height; the wood nailer will be fastened with screws with 2 rows staggered at 24" on center. Per 10 linear foot cost on the bid form is for existing wood that is unsound. The contractor on gypsum deck areas adhered each layer of insulation at minimum 8" on Center or warranty requirements of the manufacturer, whichever is more stringent. The areas that have steel decking(new) in the gypsum deck areas will have the first layer of insulation mechanically attached and the second layer fully adhered(attachment per manufacturer warranty requirements). Replace all clamping rings and drain baskets with new cast iron components. The contractor shall install a fully adhered 60 mil TPO Johns Manville, all details shall be manufacturer approved details and compliant with a 20-year warranty, there is not a manufacturer warranty but only use and installation of 20-year details for this work. The skylight on one of the office roofs we will ask for a price to remove & deck in with 20g steel decking per base scope.