Exposed Deck W/EPDM On Concrete (no Pitch)

kellry27

Question, What materials should or can be applied on a single layer of EDPM over a concrete exposed deck under 2-1/2" thick mortar setting bed under 1-1/2" thick flag stone. Water and moisture are getting thru under existing rubber membrane. We removed flagstone and setting bed and exposed the EPDM materials.I was thinking of using treated plywood over existing EDPM to elimanate some of the tickness of setting bed to ligthten the load. should I glue and screw down plywood into concrete deck and then use rigid foam panels on top for pitch? Theres no pitch. If someone could respond I would greatly appreciate your input. Thank You Gary