The Importance of Insulation Vapor Barriers

The Importance of Insulation Vapor Barriers

Insulation is designed to stop the flow of thermal energy in and out of your house. This means that insulation keeps the warm air in during the winter, and out during the summer. 

You likely already know that proper insulation can help protect your home from exorbitant energy bills. But did you know your insulation may need protection, too? 

Even with the proper air barriers, many homeowners struggle to keep water vapor from entering their homes. That's where insulation vapor barriers come in. 

What Are Insulation Vapor Barriers? 

Vapor barriers — also known as vapor retarders — reduce the rate at which water vapor can pass through a given material. In this case, vapor barriers are used to protect your home's insulation from the water vapor trying to get inside.  

Why Are Insulation Vapor Barriers Important When Insulating Attics? 

Insulation vapor barriers are important because they provide crucial protection for you and your home. Installing an insulation vapor barrier in your attic can help protect the structural integrity of your home, your HVAC system, and your family's health. 

Prevents Water Damage 

It’s common knowledge that standing water or water leaks can cause wood to rot and other serious property damage. But most people don't realize water vapor can have the same effect. An insulation vapor barrier helps protect your insulation and attic from water damage. 

Improves Energy Efficiency

Damp or wet insulation is not as good at its job and can force your home to eat up as much as twice the energy just to stay comfortable. 

By protecting your insulation with a vapor barrier, you help ensure that its quality and effectiveness are not compromised. This means your HVAC system won't have to work as hard to keep your home comfortable and can help you save on your monthly energy bills. 

Minimizes the Risk of Mold and Bacteria 

Moisture inhibits the growth of dozens of types of mold and bacteria. Insulation vapor barriers minimize the risk of mold and bacteria-related damage and illnesses. 

Types of Insulation Vapor Barriers

Vapor barriers are classified based on their permeability, or "perms.” A vapor barrier's perms are measured by how quickly water vapor is able to pass through it. The smaller the perm, the better the barrier is at keeping out water vapor. 

Although there are three classes of vapor retarders, only the first two classes are of any use when insulating attics: 

Class 1 Vapor Retarders 

Class 1 vapor retarders must have a perm of 0.1 or less. Some class 1 vapor barriers include:

  • Sheet metal
  • Panes of glass 
  • Rubber membrane 
  • Polyethylene sheet

These are the most effective — and therefore most popular — vapor barriers used in homes today. Rubber membranes and polyethylene sheets are the two most common choices since they are economical and durable. 

Class 2 Vapor Retarders 

Class 2 vapor retarders have slightly higher perms, meaning they let in more water vapor than class 1 materials. Vapor barriers in this category have perms between 0.1 and 1.0 and include materials such as:

  • Bitumen-coated Kraft paper 
  • Plywood
  • Unfaced expanded polystyrene

These materials are usually not people's first choice but will do fine in a pinch. 

Is an Insulation Vapor Barrier Right for You?

Insulation vapor barriers are ideal for homes in colder climates since they tend to produce more indoor water vapor during the extended winter months. On the other hand, if you live in a very warm or humid climate, an insulation vapor barrier will likely make your house even hotter and more humid in the summer.

Before installing a vapor barrier, make sure your current attic insulators are dry first. If they are wet or damp, you will need to replace them with new insulation before adding a vapor barrier. 

A professional can determine whether installing a vapor barrier would benefit your home and what material will provide the best protection. 

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