Commercial meat and perishable product refrigeration buildings commonly suffer from infiltration of moisture which normally occurs at the roof/wall junction where the roof meets the walls. Warm moist outside air is drawn into the cooler because of the lower pressure therein and once inside, forms ice which lowers the cooler temperature and causes freezer burn. By removing the building roof, and installing a moisture proof 40-50 mil thick sheet polymer membrane onto the cooler wall panels, over the top sill plate and the top header ledger board then welding it at the roof perimeter to the roofing membrane, an impermeable seal can be formed. To ensure the unitary integrity of the system, a flexible polymer mastic is trawled onto the wall panels before the membrane is affixed and a double sealing strip is screwed into the membrane though the mastic and into the wall panels.