CZ4A metal roofs – I use a rule of thumb of R-15 minimum (about 2.5 inch closed cell) for walls and R-25 (about 4 inch) for the roof deck. At 4 inch closed cell, the dew point stays outside the foam layer in CZ4A even on worst-case winter nights. For adhesion on galvanized metal: no primer needed if the metal is clean and dry. On painted metal it depends – fresh acrylic paint is usually fine. Old chalky paint needs light sanding first. Always do a pull test before committing to the full roof.
CZ4A metal roofs – I use a rule of thumb of R-15 minimum (about 2.5 inch closed cell) for walls and R-25 (about 4 inch) for the roof deck. At 4 inch closed cell, the dew point stays outside the foam layer in CZ4A even on worst-case winter nights. For adhesion on galvanized metal: no primer needed if the metal is clean and dry. On painted metal it depends – fresh acrylic paint is usually fine. Old chalky paint needs light sanding first. Always do a pull test before committing to the full roof.