When to Use an Attic Vapor Barrier: A Guide

Vapor barriers may not be one of the most glamorous home upgrades, but they can be one of the most important for your health and the longevity of your living space. When used in the right context, they can prevent excess moisture from accumulating in your home—and sidestep a slew of potential problems that can come along with it, like mold and mildew growth, pest infestations, health problems, and more.

Not sure when to use vapor barrier with insulation? Well, the answer may already be written in your county’s building code in accordance with the average humidity levels of your local environment. 

When it comes to your home’s integrity, what’s out of sight should never be out of mind. An attic insulation vapor barrier could ensure that those oft-forgotten corners of your home won’t be tied to its undoing. So, why is attic moisture defense so important, and how could you benefit from installing a vapor barrier in your ceiling insulation? Read on to find out.

What Is an Attic Vapor Barrier? 

A vapor barrier, also referred to as a vapor retarder, is a moisture-resistant material that can be applied inside an exterior wall, a crawl space, or an attic to provide vulnerable spaces with added protection against a potential moisture problem. 

Vapor barriers come in a variety of materials, with two of the most common options being plastic sheeting and aluminum foil.

The best vapor barrier materials and installation methods to use for a particular home typically depend on factors such as: 

  • How your home is constructed
  • What insulation building material you’re using
  • What kind of climate zone you live in

When installed with the proper care and consideration for your home and the local climate zone, an attic moisture vapor barrier can provide a critical defense in the battle against indoor moisture buildup. 

4 Reasons to Use Vapor Barriers to Reduce Interior Moisture

Generally speaking, vapor barriers are considered an essential moisture-blocking tool for climates that experience significant levels of humidity. For that reason, building codes in more humid locations will often require them, in which case you might not have much say about whether to install one or not. In drier climates, however, attic vapor barriers can be more of an optional add-on than they would be elsewhere.

Voluntary or not, the following are just some of the benefits you could experience if you decide to install an attic vapor barrier in your home. 

#1: Reduce The Risk of Mold and Mildew Developing in Your Home

In natural environments, mold and mildew play an integral role in breaking down organic materials. But when they’re present indoors on an interior surface, they can cause plenty of unwelcome damage to our homes and our health. If you find yourself wondering, “can insulation make you sick,” make sure to read up on the topic to ensure you and your family are safe against any insulation problem.

The best way to prevent mold and mildew development is to limit the condensation in your attic since the conditions they tend to thrive in include: high temperatures and high moisture levels. So, when the hot air inside your home rises or the sun’s heat radiates through your roof—and it doesn’t have sufficient insulation or a radiant barrier to mitigate it—a humid climate in your attic can become a prime breeding ground for mold and mildew.

This is a problem because mold and mildew aren’t just unsightly. When left unaddressed, they can freely feed on wet wood and other materials, potentially weakening your home’s walls and floors and leading to dangerous (or expensive) structural problems. 

Mold and mildew also enjoy feeding on:

  • Insulation
  • Carpet
  • Paper
  • Cardboard
  • Ceiling tiles
  • Wallpaper
  • Dust
  • Drywall
  • Upholstery

The Environmental Protection Agency (EPA) states that maintaining an indoor humidity level between 30% and 50% is ideal for limiting mold and mildew growth, as well as reducing the odds of pest infestations.1 

#2: Keep Your Home Protected Against Pests

Speaking of pests, it’s not just mold and mildew that thrive on warm temperatures and humidity—a number of bugs and insects do, too, including:

  • Silverfish
  • Termites
  • Cockroaches
  • Powderpost beetles

When left unchecked or unprotected, attics could fall victim to a pest infestation, potentially causing serious structural damage to your house or posing health risks to those living inside it. By limiting your attic’s moisture with a vapor barrier, you’re making your attic environment a lot less appealing to unpleasant—and downright destructive—pests.

#3: Improve Your Home’s Energy Efficiency

HVAC systems do more than cool the air in your home, they also remove moisture. That means that if your home is prone to high humidity levels, your HVAC system will have to work double time to do its job effectively, thus using more energy as a result. 

Plus, more than half of energy use in homes is used for heating and cooling,2 meaning an overactive HVAC system could have a significant impact on your energy bill—and your budget. 

Keeping your home’s humidity levels within the EPA’s ideal range of 30% and 50% could help reduce the amount of energy your HVAC system uses while it cools your home. Installing an attic vapor barrier could be one strategy to accomplish precisely that. Other ways to keep high humidity levels at bay include:

  • Reducing shower time 
  • Lowering water temperatures for showers and baths
  • Drying clothes outside whenever possible
  • Using a dehumidifier to control humidity caused by gas heaters

#4: Improve Indoor Air Quality

According to the EPA, pollutant concentrations can be two to five times higher indoors than outdoors.3 The excess moisture present in your home generates mold or mildew growth or pest infestations that further degrade indoor air quality and create or exacerbate health issues.

Whether you’re working from home or working to finish a binge-worthy series before the next season launches, it can sometimes feel like the majority of our time is spent indoors. In a home with excessive moisture buildup, even seemingly harmless activities could come with serious negative health impacts—especially if you or someone else in your household already deals with asthma or other respiratory health problems. 

Indoor mold is harmful even for those in otherwise good health. Prolonged exposure can result in upper respiratory issues like coughing or wheezing.4 However, you can mitigate these kinds of health risks by taking the following steps to limit moisture buildup in your home:

  • Using a dehumidifier
  • Repairing leaks
  • Installing a vapor barrier in your attic and/or crawl spaces

4 Tips for Installing a Vapor Barrier for Your Attic

Once you’ve made the decision to invest in a vapor barrier for your home, the key to maximum effectiveness lies in using the right insulation materials and abiding by proper installation techniques. By getting this part wrong, you run the risk of trapping more moisture in your attic, worsening the very problem you’re trying to solve. 

  • Tip 1: Consider climateWhat a “correct” installation looks like likely depends on what kind of climate you live in:
  •  In colder climates, where the home’s heating system sees more use, the vapor barrier should typically be installed on the insulation’s interior side. 
  • In warmer climates, where the home is often kept cooler, the vapor barrier should usually be installed on the exterior side. 
  • When it comes to mixed humidity climates, whether the vapor barrier should be installed on the interior or exterior sheathing of insulation might vary, but a professional will be able to determine which is best for you.
  • Tip 2: Factor in permeability – Your climate could also influence the level of permeability your attic vapor barrier will require. The vapor barrier will need to have at least some level of permeability so that moisture isn’t trapped on either side of it. 
  • Tip 3: Determine the most vulnerable side – When installing insulation with a vapor barrier, the vapor barrier should usually be applied on the side of the insulation that’s closest to where it will be exposed to the most warmth and moisture. 
  • Tip 4: Consider hiring a professional – Some homeowners may try a DIY-style attic vapor barrier installation, but as mentioned, this could come with more headaches than it’s worth. Bad ductwork installation could lead to trapping the moisture you’re trying to reduce, leading to wasted time and money and even more moisture problems than you had before. 

For some homeowners, hiring a professional to install an attic vapor barrier in a crawl space or foundation wall means more peace of mind—and expenses saved down the road. A professional will be able to evaluate the right kind of vapor barrier for your home based on the necessary factors like your attic’s construction, your local climate, and what kind of insulation you’re using.

Attic Construction: Your Hub For All Things Attics and Home Protection

When you’re looking attic cleaning in Orange County, San Diego, or Phoenix insulation installation, Attic Construction is just a phone call or email away. 

If you think you might need insulation or cleaning services for your attic space, but you just aren’t sure, we offer free attic inspections to help you assess your home’s upper-level needs. Plus, you won’t pay a cent unless a repair or service takes place. And if you’re concerned about your attic’s moisture levels, we’re happy to evaluate them in our inspection and present you with the best options for how to proceed. 

Ready to explore those options for a cleaner, healthier, and better-insulated home? Contact Attic Construction today.



  1. Environmental Protection Agency. Why and Where Mold Grows. https://www.epa.gov/mold/mold-course-chapter-2#Chapter2Lesson5
  2.  U.S. Energy Information Administration. Use of energy explained. https://www.eia.gov/energyexplained/use-of-energy/homes.php
  3. Environmental Protection Agency. Indoor Air Quality. https://www.epa.gov/report-environment/indoor-air-quality#note1
  4. Centers for Disease Control and Prevention. Basic Facts about Mold and Dampness. https://www.cdc.gov/mold/faqs.htm

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