Licensed & Insured. Crawl space Encapsulation and Mold Remediation

Where Does Vapor Barrier Go? A Homeowner’s Guide

Ever walked into a musty basement and wondered how to keep that dampness out? That’s where vapor barriers come in. They’re like an invisible shield, protecting your home from unwanted moisture.

Vapor barriers aren’t just about preventing mold or keeping your crawl space dry. There’s more at stake here – it can also improve air quality and help save on energy costs by blocking heat loss.

But the million-dollar question is: Where does this superhero of home maintenance go?

Unraveling the mysteries of vapor barriers, this guide will provide all you need to know about their role in maintaining healthy homes, selecting between different types available, learning how they should be installed for maximum efficiency, and keeping them properly maintained. 

From understanding their role in maintaining healthy homes, choosing between different types available, learning how they should be installed for maximum efficiency, to maintaining them properly – there’s plenty to uncover!

Are you prepared to explore why it’s essential to give attention to these undervalued helpers? Let’s get started!

Table Of Contents:

What is a Vapor Barrier?

You may be asking, “What’s this thing called a vapor barrier?” Well, imagine it as your home’s invisible shield. 

Its main job? To combat the villain of moisture invasion.

A material intended to impede the infiltration of water vapor is referred to as a vapor retarder or barrier. Think of it like an umbrella for your house – just not in the rain but against sneaky moisture trying to creep into places they’re not welcome.

The Science Behind It

Here comes some science-y stuff (but don’t worry, we’ll keep it simple). Moisture moves from high-humidity areas to lower ones by diffusion. This journey often leads straight through building materials such as wood frames and gypsum board, causing potential damage over time.

Vapor barriers act like superheroes here. They prevent this movement, ensuring that our homes remain dry and safe. 

Type: Class II Vapor Retarders

There are different classes of vapor barriers based on their permeability level – how much water vapor can pass through them. One popular type is “Class II”.

This includes latex paint applied thickly or plastic sheeting less than 0.1 inches thick—think birthday party tablecloth thickness—but way stronger. These guys do an excellent job at reducing air leakage and preventing mold growth due to excessive moisture.

Vapor Barriers vs Air Barriers

In case you were wondering about air barriers—they’re siblings with similar traits but unique responsibilities in the family of building materials. While vapor barriers primarily block water vapor, air barriers resist air movement through wall assemblies.

Together, they make a dynamic duo that improves your home’s energy efficiency and prevents moisture problems, which can lead to serious issues like mold growth and structural damage.

The Role in Different Climates

When it’s hot, the barrier keeps sticky outdoor air from sneaking into your cool indoors and causing dampness. But when it’s cold? It stops warm indoor air from getting into chilly wall spaces and freezing there—dodging.


Key Takeaway: 

Picture a vapor barrier as your home’s superhero, battling against moisture invasion. It’s like an umbrella shielding your house from sneaky humidity that can damage building materials over time. The popular “Class II” type is excellent at reducing air leakage and preventing mold growth due to excessive moisture.

Where Should Vapor Barriers be Installed?

Vapor barriers play a critical role as a moisture barrier, preventing moisture problems. But where exactly should they go? To effectively block moisture-laden air, these handy shields need to cover all bases.

Crawl Spaces and Basements

Let’s start with the most common spot – crawl spaces. These areas often harbor dampness due to their close proximity to the ground. According to EPA guidelines, installing vapor barriers on the walls and floor of your crawl space can keep water vapor at bay.

The same goes for basements, which are another prime target for moisture problems. A well-installed vapor barrier helps protect against potential water damage or mold growth down there, too.

Walls: The Battle Against Air Leakage

Moving up from beneath our feet, let’s talk about walls next. Believe it or not, those seemingly solid structures might actually be letting moist air slip through. 

It’s especially true if you have wood frame construction or gypsum board wall assembly because both materials tend to hold moisture.

This is where an installed vapor barrier comes into play as an effective air seal solution that keeps humidity out while also improving energy efficiency by reducing heat loss through wall cavities caused by unwanted air movement due primarily to differences in indoor/outdoor temperature.

Air Barrier vs Vapor Retarder: The Ceiling Conundrum

If we look up now, there’s one more place you might want (or not) a vapor retarder – your ceiling. Unlike lower regions of your home, like basement walls or crawl spaces that mainly battle against ground moisture, ceilings face a different challenge – air leaks. 

Where Should Vapor Barriers be Installed

In cold climates, warm, moist indoor air can leak into the colder attic space, causing condensation.

Do you have a question about installing vapor barriers in your ceiling? It’s not exactly black and white. 

Some building codes suggest using a Class II vapor retarder, like latex paint, on the inside of ceiling drywall for mixed climates or hot environments. However, others advise against it because it could lead to moisture issues if air accidentally flows from your living space into the attic.


Key Takeaway: 

When it comes to preventing moisture problems, vapor barriers are your home’s best defense. These shields should cover all bases – crawl spaces and basements, walls, and even ceilings in some cases. Installing them properly helps keep dampness out of your house while also boosting energy efficiency by reducing heat loss through the wall cavity.

Benefits of Installing Vapor Barriers

Vapor barriers can be a game-changer for your home, and here’s why. First off, they help curb mold growth. That’s right; by blocking moisture from entering your crawl space or other enclosed areas in the house, these nifty shields protect you against health hazards linked to mold exposure.

Beyond health benefits, vapor barriers also enhance air quality inside your living spaces. Moisture-laden air often carries airborne allergens and pollutants that could trigger respiratory problems like asthma. 

So imagine this: with an effective barrier installed in key areas around the house – voila. You’ve got yourself cleaner air.

Still not convinced? Well, how about energy efficiency, then?

Saving Energy with Vapor Barriers

The fact is installing vapor barriers isn’t just good for keeping things dry; it’s also great at preventing heat loss through the walls and floors of the crawl space. According to, insulation works best when air is not moving through or around it, making a vapor barrier key to reducing heating (and cooling) costs.

This means less strain on your HVAC system, which translates into reduced energy bills every month – now, who wouldn’t want that?

Maintaining Your Home’s Structure

Moisture is one sneaky enemy when it comes to maintaining our homes’ structure over time. By installing a moisture barrier system like a polyethylene vapor barrier or reinforced plastic sheeting, we give ourselves an extra layer of protection against water damage and the costly repairs that come with it.

These barriers work like a charm to keep moisture from seeping into your home’s exterior walls, ensuring their longevity. Preventing water damage is always preferable to having to fix it after the fact.

A Proactive Step Towards Home Maintenance

Putting up vapor barriers is like taking a step ahead in looking after your home. It stops mold, boosts air quality, and ramps up energy efficiency. This not only makes your place comfier but also adds value to it.


Key Takeaway: 

Installing vapor barriers in your home is a proactive move towards better maintenance. They help to prevent mold growth, enhance air quality, and increase energy efficiency. This not only makes for a healthier living environment but also adds value to your home while saving you money on repairs and energy bills.

Types of Vapor Barriers

When it comes to preserving your dwelling from water harm, not all vapor barriers are equal. Let’s explore the various types available and their unique characteristics.

Polyethylene Film

Polyethylene film, a classic choice for many homeowners, is commonly used due to its affordability and availability. It’s often found in rolls of clear or black plastic sheeting with thicknesses ranging from 4 mils (0.004 inches) up to 20 mils (0.020 inches).

The thicker variants provide better protection against punctures and tears, making them ideal for rugged environments like crawl spaces that see regular foot traffic or house heavy equipment.

Reinforced Polyethylene Sheets

Moving onto reinforced polyethylene sheets, these bring more durability into play by incorporating a layer of polyester scrim between layers of polyethylene film – think of this as armor-plating your barrier.

This type offers higher tear resistance compared to plain poly films but may be slightly more challenging to work with because they’re stiffer.

Vapor Retarder Paints

If you’re dealing with finished walls already coated in latex paint, consider using a vapor retarder paint-like coating. These specialized paints add an extra line of defense against water vapor diffusion through gypsum board wall assembly.

Air Barriers: House Wraps & Foam Boards

Last on our list are air barriers and rigid foam boards. These materials serve a dual role, acting as both air sealants to stop drafts (which can contribute to moisture problems) and water-resistant barriers that shed liquid water away from your home’s exterior walls.

While not strictly vapor barriers, they are vital components in the overall strategy of preventing moisture damage.

The Best Choice Depends on Your Needs

Considering the right vapor barrier for your needs requires careful thought.


Key Takeaway: 

Keeping your home safe from moisture damage means picking the right vapor barrier. Polyethylene film, which is both budget-friendly and comes in different thicknesses, is a favorite pick. Reinforced polyethylene sheets bring more tear resistance to the table.

How to Install Vapor Barriers

Vapor barriers, whether you choose plastic sheeting, polyethylene film or reinforced sheets, play a critical role in preventing moisture problems. They block moist air from seeping into your crawl spaces and causing water damage.

Step 1: Preparing the Space

The first step is cleaning out your crawl space thoroughly. Make sure all debris is removed because sharp objects can puncture the vapor barrier.

This also gives you an opportunity to check for existing mold growth, which could be a sign of previous water infiltration. If any mold is found, professional help should be sought for safe removal before proceeding with installation.

Step 2: Measure and Cut Your Barrier Material

What is your next move? Measure up. You need accurate dimensions of your crawlspace walls and floor so that you can cut the right size pieces of vapor retarder material.

When cutting, remember it’s better to have extra than not enough, as overlaps are essential when installing vapor barriers properly.

Step 3: Installation Process Begins.

Lay down the barrier on your crawl space floor, starting at one corner. Let it extend about six inches up each wall, creating an air seal against possible air leakage due to differences in air pressure between outside and inside environments. 

Step 4: Overlapping and Sealing

The real trick to making a vapor barrier effective is ensuring all seams are overlapped by at least six inches, then sealed with waterproof tape or caulk. This prevents water vapor from sneaking through gaps between sheets.

Step 5: Securing the Barrier on Walls

Finally, make sure to fasten your barriers onto the crawlspace walls using furring strips or similar materials. They must be securely attached.


Key Takeaway: 

Start by tidying up your crawl space and doing a mold check before installing the vapor barrier. Then, get precise measurements and cut out the barrier – it’s always wise to have more than less. Begin laying down the barrier from one corner, making sure it extends six inches up each wall.

Maintenance of Vapor Barriers

Proper maintenance is the secret sauce to prolonging the life of your vapor barrier. Regular checks are a must. Let’s dive into some handy tips.

Regular Inspections

Set aside time for inspections at least twice a year. Periodically observe for evidence of deterioration, like tears or splits in your plastic sheeting or polyethylene film.

Dampness? That’s a red flag, too. It means moisture has found its way past your vapor retarder. 

If left unchecked, this could lead to mold growth and water damage.

Patching Up Problems

If you spot an issue during inspection, don’t panic – but do act fast.

A small patch kit can fix minor holes or tears easily.

This quick fix will prevent further air leakage, which can compromise energy efficiency.

Vapor Barrier Replacement

Sometimes, it’s more than just minor wear and tear. Your vapor barrier may need replacing entirely if there are significant issues like large-scale ripping or moisture problems that cannot be fixed by patchwork alone.

The replacement process might seem daunting, but think about it like changing out old gym shoes: sometimes you’ve gotta let go to get something better.

Hiring Professionals

You might prefer calling in experts when dealing with serious issues like extensive mold growth caused by faulty barriers preventing proper airflow.

Professional services offer comprehensive solutions, from diagnosing the problem to fixing it and ensuring your barrier is back up to standard.

Companies like Crawlspace Makeover provide excellent vapor barrier maintenance services that could save you time, money, and a lot of headaches down the line.

In conclusion, keep an eye on your vapor barriers. Regular checks can help spot problems early and extend their lifespan.


Key Takeaway: 

Keeping your vapor barrier in top shape is a mix of regular inspections, timely patch-ups for minor issues, and sometimes even full replacements. When the problem’s too big to handle alone, professionals can step in to save you time and money. Remember: routine checks are your best defense against moisture problems.

FAQs in Relation to Where Does Vapor Barrier Go

Where should a vapor barrier be placed?

Vapor barriers go in crawl spaces, on walls, and on floors. They block moisture from entering enclosed areas.

Does the vapor barrier go over or under the insulation?

The vapor barrier usually goes on the warm side of the insulation. This prevents condensation inside it.

Should vapor barriers go up walls?

Absolutely, Vapor barriers should extend up the walls of your crawl space to prevent moisture intrusion.

Where does the vapor barrier go in the slab?

In slabs, you put the vapor barrier right below the concrete layer to halt ground moisture from seeping through.

Deciphering the Ideal Locations for Vapor Barriers

We’ve delved into what these moisture fighters are and how they play a crucial role in safeguarding your home from unwanted dampness.

Throughout this guide, we’ve uncovered the essential areas where these barriers play a pivotal role. Ensuring they are correctly positioned can mean the difference between a home that is resilient against moisture-related challenges and one that succumbs to them. 

From crawlspaces to walls, the right placement can optimize insulation, prevent mold growth, and safeguard your home’s structural components.

If you ever find yourself in doubt, seeking professional advice can provide clarity. Remember, a vapor barrier is more than just a sheet; it’s a shield, and placing it correctly magnifies its protective prowess.

While knowledge is your first line of defense, skilled hands make the real difference. As you think about where your vapor barrier should go, also ponder on who should do the installation. Call Crawlspace Makeover today, and let your home benefit from a makeover that’s both protective and professional.

Picture of Greg Lewis

Greg Lewis

Greg Lewis is the founder and CEO of Tier Restoration, a company dedicated to restoring the indoor environment of homes and businesses experiencing water damage, smoke damage, or mold contamination.

Greg has spent most of his life working in this industry in Nashville, Tennessee, in the 1970s, working in his father’s commercial cleaning business, in the 1980s and 1990s as a partner with his father in the Sears Carpet and Duct Cleaning franchise, then on his own since 2000.

Greg played his trumpet at Overton High School and the University of Tennessee, Chattanooga, and you can still find him playing throughout the Greater Nashville, Tennessee area.