Condensation and the Metal Roof

Water will condense on the warm side of a metal roof deck when the warm air comes into contact with a cold roof deck.  

Condensation is a complicated problem for building designers, HVAC contractors, roofing contractors, window installers, and other building envelope contractors. 

It isn’t uncommon for a building to change occupancy usages, heating and air conditioning setups, and other design changes. Suddenly, the building owner starts having to deal with “roof leaks” and other water problems originating from condensation problems that didn’t exist prior to the design changes.  

One example described next is from a building in Oklahoma City that had major usage and design changes.

The building is very large and is utilized as a warehouse. The building was not heated or air conditioned and had insufficient insulation installed, and it was purchased by a commercial kitchen designer and installer. The buildout included installing an office and showroom plus a high output heater in the warehouse. 

The building owner called me with a chief complaint of water dripping on his drop ceiling tiles.  There was batt insulation installed above the drop ceiling. The metal roof deck had some insulation; however, the insulation was not well adhered or fastened, and much of it was missing.

Prior to calling me, the building owner called another roofing company who applied a roof coating. The problem wasn’t a leaking roof, so the problem continued, and the building owner’s money was wasted.

I proposed two solutions to building owner. The first and most expensive option was to install a poly-iso insulation above the roof deck and then a TPO roof for waterproofing. The second and less expensive solution was to install on the underside of the metal roof deck 1.5” of closed cell spray foam insulation, and then another 2” of open cell foam insulation. 

The owner chose the less expensive second choice. This solution prevented the warm heated air from coming into contact with the cold metal roof. Thus, no condensation occurs on the structure’s underside roof deck any longer.

I am often asked to look at roofs on buildings with condensation problems. Certainly, roof design can prevent condensation. By installing roof insulation above the roof deck, the cold outside air is prevented from cooling the roof deck, causing a temperature gradient with the warm (inside) air. This will also stop roof deck condensation.

The current building code requires R-20 above the roof deck in Oklahoma City. This code is not only about energy savings; it also addresses building condensation.