BY MARK MULLINS, FABRAL
We have all had, or know someone with, condensation associated with metal roofing. As suppliers and installers, we really need to consider the building construction and use to determine the best method of controlling condensation. We also should be having conversations with our customers and end users about condensation. The condensation control measures can and most likely will affect cost, so we want to be sure that the owner is in the loop with this. I am a big fan of educating the customer and letting them make the decision about which route to go.
Condensation is caused when moist air inside a structure comes in contact with the underside of the metal. Metal does not “sweat”—the moisture must be introduced from another source. It can be from cooking, showering, etc. for residential projects or humidity, moisture from the ground, animals, etc. for post frame structures.
We have traditionally had three weapons in the battle against condensation; they include: Ventilation, Insulation and Vapor Barriers. Venting is a way to remove the warmer, moist air from the structure. For this method to work properly, we really need to ensure open air flow from eave to ridge. Insulation is used to keep the attic space as close to the outside air temperature as possible; this is really only applicable to heated and cooled structures with an attic such as a home. Vapor barriers are used to prevent the moist air from getting to the back of the metal panels; again, these are typically used on projects with a solid deck such as a home.
This leaves the question about what to do with open framed structures that typically have no attic space to vent or solid deck to apply a vapor barrier. There are insulation blankets that can be used between the purlins and the metal roof panels, but there are alternatives to this available in the market. There are condensation control products that are applied to the back of the metal panels during the fabrication process. Many of these materials require additional work during the install, but there is one that does not. When researching these alternative products, be sure to ask if additional steps need to be taken during the install to retain the warranty.