Does My Roof Need a Vapor Barrier?

There are many layers to a roof system that each play an important role in the system’s integrity. Essentially every flat roof has a roof deck, layers of insulation, and a mechanically attached or adhered roof membrane. But sometimes, a vapor barrier between the insulation and membrane is necessary to avoid costly repairs.  

What Does a Vapor Barrier in a Roof System Do? 

The main purpose of a vapor barrier is to avoid condensation forming within the roof system. If condensation does begin to form, it can lead to mold growth, insulation damage, and the deterioration of your roof system. 

Does Every Roof System Need a Vapor Barrier?  

No, not every roof system needs a vapor barrier. The need should be evaluated on a case-by-case basis based on the following circumstances: 

1. Building use: What is going on inside the building can determine what the system looks like on top of the building. If your building has high interior humidity, for example, in food processing plants, manufacturing certain products, or data storage, you’re likely to need a vapor barrier on the roof. 

2. Climate: The climate of the area you’re building paired with the building’s use will affect whether or not you need a barrier. Generally, very cold winters or hot, humid summers might warrant a vapor barrier to avoid driving vapor up through the roof assembly.  

3. Code compliance: Depending on the facility that you’re building, there’s a chance that, depending on the circumstances above, you must have a vapor barrier in your roof system in order to meet code requirements. 

Does A Vapor Barrier Keep Rain from Penetrating through the Roof? 

No, the purpose of a vapor barrier is not to keep rain out, but rather to stop moist air from inside the building from moving upward into the colder roof layers, where it could condense into water. The roof membrane, its drainage system and the metal components all work together to keep your building dry. You do not need a vapor barrier in order to keep rain out.  

I’m Still Unsure. Who Can I Reach Out To?  

At Mid-South Roof Systems, we specialize in installing, repairing and maintaining commercial roof systems across the nation. We have the experience and knowledge to direct your roofing decisions, so you don’t have to do any guesswork. Reach out to our team via phone, email, or our contact form to get your commercial roofing questions answered quickly.