1. Article Body
A cold storage roof is the one commercial roof where the standard rules are reversed. Understand that single point and the rest of the building type makes sense.
Vapor drive runs inward
On an ordinary heated building, warm moist air inside pushes outward toward the cold exterior, so the vapor retarder goes on the warm side, near the interior.
On a freezer or cooler, the interior is the cold side. Warm humid outdoor air pushes inward, toward the refrigerated space, continuously, all year, and hardest in summer.
That reverses the assembly. The vapor retarder belongs on the warm side, which on a cold storage building is above the insulation rather than below it.
Get this wrong and the building fails, not the roof covering.
What failure actually looks like
Moisture driven into the insulation reaches a point cold enough to condense, and then to freeze.
Ice forms inside the assembly. It does not drain, it accumulates. Over seasons it saturates the insulation, destroys its thermal value, adds enormous weight and can lift or distort the deck.
The visible symptoms arrive late: rising refrigeration energy cost, ice at the underside of the deck, frost at fasteners, and eventually structural concern.
By the time it is visible from inside, the assembly has been failing for years.
Continuity is everything
A vapor retarder works only if it is continuous. Any break lets vapor through, and vapor finds every break.
That makes penetrations the governing problem. Every pipe, conduit, hanger, drain and curb is a potential path, and each one has to be sealed to the vapor retarder as well as to the water barrier.
The design principle on a cold storage roof is to minimize penetrations rather than to detail them well. The best penetration is the one that was routed elsewhere.
Thermal load and insulation thickness
Cold storage carries far more insulation than an ordinary commercial roof, because the temperature differential is far larger and refrigeration energy is the dominant operating cost.
Thicker assemblies mean taller curbs, different terminations and more attention to thermal bridging at every fastener.
The refrigeration equipment
Condensers and evaporative equipment sit on the roof and carry heavy loads, substantial piping and continuous condensate.
Refrigeration piping penetrating a cold storage roof is a particular concern, because it is cold, it will attract condensation along its length, and it has to be sealed and insulated where it passes through.
You cannot simply shut it down
A freezer cannot be defrosted for a reroof without moving the product or accepting loss. That constrains scheduling severely and makes phasing a product logistics exercise.
What to establish first
Operating temperature. Where the vapor retarder sits in the existing assembly. Penetration count and what each serves. Whether refrigeration energy use has been rising. Whether any ice has been observed inside.
