roof work notes
Not Every Wet Roof Is a Leaking Roof
Plenty of the moisture problems we open up on Columbia commercial roofs never came through a hole. They came up from inside the building. Columbia spends its summers in a hot, humid subtropical pattern, and the buildings beneath these roofs run cold air hard for months. That pressure difference drives water vapor upward through the assembly, where it meets cooler surfaces near the membrane and condenses inside the insulation. The result looks like a leak, behaves like a leak, and gets misdiagnosed as one, while the real culprit is the building's own humidity working against a vapor barrier that was placed wrong, damaged, or never installed at all.
We see this across the Midlands building stock: refrigerated and food-processing space in the Pineview and Shop Road industrial corridors, hotels and restaurants along the Harbison Boulevard belt near Columbiana, natatoriums and laundry-heavy facilities, and older office and institutional buildings near the Vista and the University of South Carolina that were re-covered over the years without anyone ever checking which way the vapor was moving. When the diagnosis is wrong, the repair fails fast, because patching the membrane does nothing about moisture that is arriving from below.
What Trapped Moisture Does to the Assembly
Interior humidity damages a roof from the inside out, and the symptoms follow a recognizable order. First the membrane blisters: vapor pressure builds beneath the sheet and lifts it off the substrate in soft, rounded bubbles that flex underfoot and eventually split. Then come ridges, long raised lines that telegraph up through the membrane where saturated insulation boards have swollen, curled, and pulled apart at their joints. Underneath all of it, the insulation itself is the real casualty. Once a polyiso or fiber board takes on water it loses most of its R-value, so the building bleeds conditioned air through the roof, the HVAC works harder, and the moisture keeps feeding the cycle.
Left alone, it reaches the deck. On the steel decks common under Columbia low-slope roofs, constant moisture starts corroding the top flutes and the fasteners that hold the assembly down, and corrosion does not reverse. A roof we could have saved with a targeted cut-and-replace at fifteen percent wet becomes a full tear-off, deck repair and all, a season or two later. Catching it early is the entire difference between a repair invoice and a replacement project.
The Vapor Barrier Is Usually the Real Problem
In a cooling-dominated, humid climate like Columbia's, vapor generally drives upward from the conditioned interior toward the roof, which means the vapor retarder belongs low in the assembly, at or near the deck, ahead of the insulation. When a building has the retarder in the wrong plane, or a torn one, or none, the assembly becomes a trap: vapor gets in, hits the cold underside of the membrane, condenses, and has nowhere to dry to. Recovering over an assembly like that without fixing the vapor management simply rebuilds the same failure inside a brand-new roof. We will not do that, because it wastes the owner's money on a roof engineered to fail again.
