Install the vapor barrier on the warmer side because vapor always moves from high to low pressure. This serves as a moisture barrier. It ensures water vapor will not enter the insulation layer. Also, it will not condense or freeze in the insulation layer to damage the insulation performance. Proper installation of this moisture barrier is crucial for maintaining the structure's integrity.
Placing the vapor barrier on the colder side allows water vapor to penetrate the insulation. This reduces the insulation's effectiveness and causes damage.
Where should we install the vapor barrier—on one side of the insulation, or on both?
In China, there has a vast territory with a large temperature difference between north and south. This depends mainly on the temperature inside the cold storage. The climate where the cold storage is built—whether it's very cold, cold, or warm—also matters. If the hot and cold sides of the wall can reverse, install the vapor barrier only on the warmer side of the insulation.
If the inside is sometimes hotter than the outside (such as controlled atmosphere storage in many places in the north and low temperature storage in the northeast), you should consider installing moisture-proof and gas-proof layers on both sides of the insulation layer. This will create an effective moisture barrier.
Using pre-coated steel or aluminum sandwich panels for cold storage construction results in panels with zero water vapor permeability. Their ability to resist vapor penetration—in other words, their vapor permeability resistance—is infinite. This effectively eliminates water vapor penetration. Regardless of the insulation layer's thickness, condensation will not occur inside. In this case, a vapor barrier is unnecessary. However, the panel seams should still be sealed with a high-quality sealant. This will ensure no gaps in the moisture barrier.
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