Application When used as Roof Overlayment: Fiberboard panel joints should be offset at least 6" (152.4mm) from underlaying insulation panel joints. Panels must be installed with 1/8" (3.18mm) (maximum) space at all joints. Panels must be dry before and during application. Apply only as many roof fiberboard panels as can be covered by a roof membrane during the same day. When used in Re-Roofing applications: Before applying recover board, existing roof surface must be cleaned of all gravel and other debris. Surface irregularities must be smoothed or scraped flat. Deck must be dry at start of application and maintained in a dry condition during re-roofing.  Return to Regular and High Density Fiberboard Insulation