When you own a home, it makes sense to know a little about its construction and 
why certain things are done like they are. And when you notice symptoms of something “not quite right,” you are correct in questioning the cause and seeking professional advice. This post describes why a vapor barrier is so important to protecting your home, the symptoms of a failed or missing vapor barrier to look out for, and who to call if you discover an issue.
What is a Vapor Barrier?
A vapor barrier is a material or layer designed to prevent moisture from passing through your home’s walls, floors or roof. Typically, it is made of a plastic or foil sheet that is installed on the warm side of an insulation system—in other words, between the interior space’s finish materials such as its drywall or plaster and the insulation.
The purpose of a vapor barrier is to prevent water vapor from condensing within the walls, floors or ceilings, a problem that can lead to mold growth, building materials deterioration and decreased energy efficiency. By reducing the amount of moisture entering the home, it can also help improve indoor air quality.
In new construction, the vapor barrier is typically installed after framing and before insulation and finish materials according to manufacturers’ instruction and local building codes. In a retrofit or renovation project, it may need to be installed as part of the insulation upgrade or as a separate retrofit measure. This can be more difficult and expensive than installation during construction, especially if the building envelope needs to be opened up to access the interior side of the insulation. Your construction professional will advise you on the best route to take.
It is important to note that the placement of a vapor barrier is just one part of a comprehensive moisture management strategy. Other important considerations include proper insulation, ventilation and air sealing, along with the use of moisture-resistant materials and indoor humidity level controls.
The Difference Between a Vapor Barrier and a Vapor Retarder
A vapor barrier and a vapor retarder, although these descriptions are often use interchangeably, have notable differences.
- Vapor barrier: A material with a low permeance or resistance to water vapor diffusion, typically less than 1 perm. Its purpose is to prevent the movement of water vapor through building materials such as walls or ceilings to control interior moisture levels.
- Vapor retarder: A material with a moderate resistance to water vapor diffusion, typically between 1 and 10 perms. It is designed to slow down the movement of water vapor rather than completely stop it, and is often used in conjunction with other building materials such as insulation to help control interior moisture levels
The Signs and Problems of a Missing or Incorrectly-installed Vapor Barrier
If your home’s vapor barrier is absent or hasn’t been installed correctly, it can lead to moisture problems within the building. Without it, warm, moist air from indoors can penetrate into the walls, ceiling or floor cavities and condense into liquid water as it comes into contact with cooler surfaces such as the sheathing, studs or rafters. This can lead to a variety of issues such as:
- Condensation. If you notice condensation on windows or other interior surfaces, it can be a sign that your vapor barrier is not effectively working.
- Mold growth. Mold can grow on organic materials such as wood, paper, leather or fabric when moist for a period of time. It can cause health problems as well as building damage.
- Wood rot. When moisture penetrates the wood framing, the rot can weaken the structural integrity of the home.
- Decreased insulation performance. By displacing air and filling the air pockets with water, the R-value of your insulation is decreased.
- Peeling or bubbling paint and wallpaper. Moisture can cause your wall coverings to peel, blister or discolor.
- Warped or damaged flooring. Moisture could be accumulating in the subflooring.
- Unpleasant environment. Moisture problems can cause musty odors, or a feeling of dampness or discomfort.·
A Building Pathologist Can Help Discover a Faulty Vapor Barrier
A building pathologist is a professional specializing in investigating and identifying problems with buildings, including moisture-related issues that can be caused by a faulty vapor barrier. They may use various techniques to identify the problem, including:
- Visual inspection. The pathologist will visually inspect the building envelope looking for signs of moisture intrusion or damage, like water stains, mold growth or peeling paint or wallpaper.
- Moisture testing. Moisture meters, infrared thermography using infrared cameras, or other testing methods can detect moisture levels behind walls, ceilings and floors.
- Air leakage testing. Blower door testing or other methods to test for air leaks can indicate areas where moisture may be entering the home.
- Materials analysis. The pathologist may analyze building materials such as drywall or insulation to determine if they are wet or damaged due to moisture intrusion.
Suspect a Vapor Barrier Leak or Improper Installation? Contact Först Consulting Group.
The Washington DC metropolitan area has a humid, subtropical climate with hot, muggy summers and mild winters, which can create moisture problems in a home if proper building techniques and materials are not used.
If your home is showing signs or symptoms of a faulty vapor barrier, it’s time to call Först Consulting Group. We specialize in building pathology inspections to help homeowners throughout the Washington DC corridor (DMV) discover issues that can potentially damage their homes, or support claims against a faulty installation or an unscrupulous contractor.
Contact Först Consulting Group by completing our online contact form and let’s have a conversation.
