A Closer Look At Vapor Barrier Insulation

Vapor barrier insulation

Do I need vapor barrier insulation? Good question. Atticare specializes in insulation and attic and crawl space services so there’s not a lot we don’t know about vapor barrier installation.

Let’s look at why insulation with a vapor barrier is important, and how it can help different areas of your home.

What’s Wrong With Insulation With No Vapor Barrier?

Across the country, the most common type of insulation is made of fiberglass. It comes in rolls and pre-cut sheets known as batts. You can see it’s soft and absorbent.

In dry climates, this traditional fiberglass insulation is fine by itself. However, if the climate is damp or humid, we have a problem. In these conditions, moisture can penetrate the insulation and cause no end of problems.

Over time, damp insulation can cause serious structural problems to your home. In addition, you can get mold, mildew and toxic air.

What Is Vapor Barrier Insulation?

Vapor barrier insulation is a type of moisture-proof insulation. It has a waterproof lining on one side which is usually made of polyethylene.

It goes over the top of regular insulation and keeps it dry, along with the structure of your building.

Whether To Use A Vapor Barrier With Insulation According To Where You Live

What’s the humidity like? If you live in a very dry place then insulation with a vapor barrier is unnecessary.

Atticare carries out quality vapor barrier installation across New Jersey, the San Francisco Bay Area and Los Angeles. And all these locations suffer from some degree of humidity.

New Jersey

Most of New Jersey is classed as having a humid subtropical climate, and humid continental in the north west. The humid summer and snowy winter make the air very moist.

San Francisco Bay Area

The San Francisco Bay Area is unsurprisingly very damp because of that sea air. In fact, the average humidity is a sticky 75%.

Los Angeles

It’s generally dry in Los Angeles, but summer is humid because of evaporation from the ocean. The average humidity is 65% which feels pretty muggy.

How Does A Vapor Barrier Work?

Vapor barriers protect interior walls from excess moisture. And this is particularly useful in humid climates, and rooms which get damp. Normally these are bathrooms, basements and kitchens.

When it’s cold outside, the damp air inside your home will naturally try to head outside. The problem comes if it can travel through your walls.

If moisture gets into your walls, it can condense into water or ice. This causes no end of structural problems including rot, mildew and cracking.

Do You Need A Vapor Barrier With Insulation?

Is there no vapor barrier in your attic? Then the damp air is free to pass through the walls when it’s cold outside. Insulation with a vapor barrier plus a good attic vent is the best way to keep the moisture from entering your walls.

As you can imagine, traditional fiberglass insulation is able to absorb a lot of moisture. But that’s really bad. Why? Wet insulation can’t do its job properly, and mold can grow on the underside, too.

Waterproof vapor barrier material will keep moisture from entering your insulation. So it stays dry and insulates effectively.

Vapor Barrier Installation In Different Parts Of The Home


The attic is where all that warm damp air rises to, if left to its own devices. Sounds OK until that air gets stagnant.

This sounds gross because it is. In addition, humid, stagnant air can aggravate allergies and respiratory conditions. So it’s vital to plan adequate attic ventilation along with the vapor barrier.

Crawl Spaces

You can lay polyethylene vapor barriers over the ground directly below the crawl space. It keeps pests out and the area stays drier.

Learn more about crawl space vapor barrier installation here.


To prevent moisture from outside entering, vapor barrier insulation can be laid against the walls of your foundation.

Foundations that are kept dry don’t risk cracking or bowing, like they are if they’re exposed to excess moisture.

Installing Fiberglass Insulation With A Vapor Barrier

Here are some pointers whether you want to install roll or batt insulation with a vapor barrier. Batts are just pre-cut sections of fiberglass insulation, the material is the same as for rolls.

#1. First things first, the attic, wall or foundations should be totally sealed of any cracks or spaces where pests or moisture could enter.

#2. You cannot simply install a vapor barrier over existing fiberglass insulation. This is because the old insulation might already contain some moisture, which then gets trapped. We need to install it over new insulation, so that you know it’s dry and clean.

#3. We apply the vapor barrier material over the side of the insulation facing you.

#4. There shouldn’t be a vapor barrier on both sides of the insulation. In fact, it needs the other side exposed in order to dry out if necessary.

Can I Install A Vapor Barrier Myself?

Installing a vapor barrier is a big, complex job and needs to be done right, by a licensed team like Atticare.

Homeowners can make costly mistakes with vapor barriers and end up making the moisture and mold problem even worse.

You can also waste a lot of money on materials if you’ve never installed a vapor barrier before. Electricity bills can be through the roof too, if it’s not done correctly.

The Importance Of Moisture Control

Our goal isn’t total moisture elimination. It would be impossible anyway, given the humid climates where we work in California and New Jersey.

The homeowner and vapor barrier team should focus on keeping water vapor at a safe and controlled level. This means we install good quality vapor barriers in addition to maintaining effective ventilation.

These simple moisture control steps will protect the structure of your home for years to come.

Get In Touch With Atticare For Professional Vapor Barrier Installation In Your Home

Atticare is a top-rated and fully licensed insulation contractor. We’re proud to serve customers in the San Francisco Bay Area, Los Angeles and New Jersey. Ask us anything about getting insulation with a vapor barrier at your home!

Give us a call to set up your free consultation at (866) 692-5449 or contact us here.


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