Does Thickness Matter when it comes to Vapor Barriers?

crawlspace vapor barrierIf you’ve come to the realization that you need to encapsulate your crawl space, you’ve already taken a step in the right direction. The benefits of crawl space encapsulation are many. It improves the quality of the breathable air in your living spaces. It decreases home energy consumption all-year round. It stops pests and rodents from entering your home and damaging it. And it makes a potentially useful storage space where you can keep items at a relatively stable temperature and humidity level.

But after you’ve made the decision to get your crawl space encapsulated, there are a few decisions you must make. One of them is what thickness the vapor barrier should be.

First, let’s step back and talk about just exactly what a vapor barrier is. Typically, a vapor barrier is made of a plastic. To be more specific, it’s called polyethylene. Polyethylene is a thermoplastic polymer that is one of the most widely used plastics in the world. It comes in a variety of densities and is used in all sorts of applications such as plastic tubing, garbage cans, grocery bags, and even plastic wrap.

When it comes to vapor barriers, the polyethylene used varies between 6 mil and 20 mil. Mil is a unit of measurement equal to 1 thousandth of an inch. To give you an idea of how thick that is, here are some every day items you would encounter, and their thickness:

— Stretch Wrap: .8 mil

— Plastic grocery bag: 25-3 mil

— 10 pieces of paper: 10 mil

— Credit Card: 30 mil

— Dime: 53 mil

With vapor barriers, it’s important to have a thicker rather than thinner mil thickness. Why? Because you want a material that accomplishes a few things. First, it needs to be durable, meaning puncture and tear resistant. Second, it needs to have low permeability. Permeability refers to the material’s resistance to water vapor pass-through. If a vapor barrier has low permeance, that means that very little if any water vapor is passing through the material. This water can contain mold spores, which can make your family and you sick if exposed for an extended period of time. It can also carry with it foul odors from the soil as well as fungi that can rot the wood structure of your home. By sticking with a thicker mil plastic, you’ll have a dryer crawl space and better air quality.  We recommend using a vapor barrier of 16 mil or higher. This translates into a permeance rate of only .0015 This is considered impermeable in American building codes.

The other thing you should look for when choosing a vapor barrier product is how that barrier is constructed. Better vapor barrier products incorporate a woven pattern into the sheeting to make it more durable.  This translates into higher tensile strength. Most thicker mil vapor barriers have higher tensile strength, but it’s a question you’ll want to ask your crawl space encapsulation company.

Also, if you can, you should look for one that is fire retardant or has a Class A fire rating, the best fire rating for materials. The last thing you want is to install a product in the lowest part of your home that is easily flammable.

Can I walk on it?

This is a question you should also ask when interviewing companies. For many homeowners, using the crawl space for storage necessitates walking on the vapor barrier from time to time. If you use a thicker vapor barrier, you’ll be able to walk on it. However, you should consider installing dimple matting below the actual vapor barrier. Dimple matting is again a polyethylene product that is “dimpled” with small circular indentations. It’s thicker and more rigid than the vapor barrier itself and therefore can be walked on. The added advantage of dimple matting is that it creates a pathway for water to drain toward the installed sump pump. Without it, water may stay trapped underneath the vapor barrier itself, which you don’t want.


The thickness of your vapor barrier is just one of the many considerations you need to take into account when installing a crawl space encapsulation system. It’s important to choose a company that is experienced in doing this type of work and has a track record of happy customers. If you’d like more information about installing a vapor barrier in your home, contact Dr. Crawlspace at 971-275-2920.