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Selecting a Crawl Space Vapor Barrier

When selecting a vapor barrier for your crawl space, knowing a little bit about the vapor barrier and how it is made is crucial. There are many options available today like cord reinforced, woven along with the traditional non reinforced. In this article we will discuss the differences in makeup, quality, strength and service life. 

Overview

Because we want to keep on track with the subject at hand we will not be covering products like tarps, used advertising banners or gimmick liners. We will be discussing only band new, first use products that were manufactured for the purpose of crawl space enclosure.

Cord Reinforced

Crawl Space Vapor Barrier
Cord Reinforced

First up is probably the most well known and recognized option cord reinforced crawl space vapor barriers. This product, like others, has knock offs floating around in the market. Usually really cheap compared to most other options and the supplier does not take close up pictures of the product or offer samples to highlight the quality. If you are going to spend even $200 on product for your crawl space you should be offered a sample of the product to approve the quality. 

Lamination

Cord reinforced is made by laminating two different films together with a polyester cord in-between the film. This lamination process is not glued or bonded by some other chemical, at least not the quality vapor barriers. Polyethylene does not accept glue well at all and if a product was glued together it would have an off gassing smell and come apart rather quickly. Instead, the proper way to laminate the layers is to use hot melted virgin polyethylene as a tie layer. This method permanently bonds the two film layers together. 

Reinforcement

The cord in the cord reinforcement is made from polyester and is rated at 1000 denier. The cord adds tear strength resistance in both directions. Many bias ply tires use 1000 denier cords to keep the tire together at highway speeds. Often the cord is separated in a diamond or square pattern about 1/2' to 3/8" apart. 

Smell
Tested Pure




Because import and other low quality cord/string reinforced products have entered the market there are many warnings about an odor coming from this type of vapor barrier. It is very important that you make sure which ever vapor barrier you used or have installed in your crawl space has been Tested Pure™ certified to be sure there will be no odors coming from the plastic vapor barrier. Both SilverBack® and GuardianLiner® SR are Tested Pure™ certified and every roll comes with a certificate when the products are registered for the 30 year warranty.

Coated Woven

Woven vapor barrier
Coated Woven

Woven products (also known as coated woven) have been on the market since 2012 but have made a bigger run at the market share since 2019. This product, in its most available form, is made by coating a tarp like weave with a 1 mil polyethylene layer on the top and bottom. This vapor barrier had gotten its early popularity mostly because it was less expensive than the cord reinforced, but as its demand began to rise so did the price

20 Mil Vapor Barrier
SilverBack®

The advanced versions of the coated woven are the SilverBack® HS (high Strength) and GuardianLiner® HS brands. What makes them advanced is these two brands use a 4 mil film on the white side with a 1 mil tie layer instead of just a 1 mil coating. This 4 mil film greatly increases the wear layer of the product, thus improving the wear and tear of crawling on it in a crawl space.

Reinforcement

The reinforcement of this type of vapor barrier is made from cross weaving polyethylene ribbons. Products like the SilverBack® and GuardianLiner® stretch the ribbons to strengthen them before weaving. The weaving greatly improves the tear resistance from both directions. 

Smell

Like the cord reinforced the best way to avoid having an odor problem make sure you are buying a Tested Pure™ certified vapor barrier. Cheap imported and products meant to be used outside can cause and odor problem in your home.

Non Reinforced

10 Mil Vapor Barrier
Pure Guardian™

Non reinforced plastic sheeting has been around since plastic was invented. There are many quality differences between one roll to the next. Many products in the category are meant for a short life such as a paint drop cloth or dust cover. These products are usually made of 70%-90% recycled polyethylene and offer no protection for a long service life. In fact they are meant to break down easily in the landfill once they have served their purpose. 

The Difference

Non reinforced vapor barrier for use in a crawl space will work very good, provide you are using a 100% virgin polyethylene film and you make sure it is Tested Pure™. Make sure you use at least an actual 10 mil on the floors in a low traffic crawl space. The walls can be as thin as 6 mil, but there is very few high quality 6 mil's on the market. Many people use 10 Mil Pure Guardian™ on the floor and 8 Mil Pure Guardian™ on the walls. 

Thickness

Most asked question on crawl space vapor barrier selection is "what thickness do I need?". The traffic in your crawl space will determine what thickness you should use.

If your crawl space does not have a water heater, air handler, duct work, plumbing or any other reason to get in the crawl space then you can use a thinner mil vapor barrier like the 10 mil Pure Guardian™. However, if you have all of these items in your crawl space then a highly durable vapor barrier like the 20 mil SilverBack® or 20 Mil GuardianLiner® are more appropriate. And if you have some but not all of these in your crawl space then the 12 mil GuardianLiner® or 12 mil DiamondBack™ will work vary well.