Vapor Barrier Installation

Crawl Space Vapor Barrier Installation

6-mil Vapor Barrier aka is the most common moisture barrier used today! It is great to prevent moisture problems from occurring and causing damage. Moisture is constantly trying to vaporize into the air so it is critical to isolate the home from the earth as best as possible. If no moisture barrier is present, your home is at risk for high wood moisture content which in turn can cause mold growth, wood rot, and structural issues including: sagging floors, sticking doors, and other crawl space issues.

  1. Vapor barriers should always be fastened to the ground to prevent it from moving around
  2. Vapor barriers (6-mil) should never be used for an encapsulation aka un-vented crawl space (it will fail and does not meet code)
  3. Vapor barriers should always be installed as close to 100% ground coverage as practical
  4. Vapor barriers should never be installed on top of an existing moisture barrier or debris (it shows laziness and can compromise the system)

Steps For Professional Vapor Barrier Installation

  1. Clean out the crawl space – remove any plastic, debris, or sharp rocks from the ground
  2. Crawl space grading – level the ground of the crawl space to make the surface flat
  3. Take measurements – assess the space and plan to work around obstacles
  4. Prepare the vapor barrier – cut the liner and roll it up in preparation to install
  5. Stage the liner and roll it out – roll out the poly and cut tight around obstacles
  6. Keep plastic tight and cover 100% of the ground with the vapor barrier
  7. Stake the vapor barrier to the ground around obstacles and along walls

Types Of Vapor Barrier


The mil of a plastic is simply the thickness of the plastic. Here is a quick guide on the uses of sheet plastic by ‘Mil’. One Mil = 0.001 inches.

2 mil poly (light duty): paint protection, as a dust barrier, or a drop cloth. Not to be used in a crawl space.

4 mil poly (medium duty): vapor barrier in between insulation and drywall. Can also be used as a drop cloth or a temporary cover. Not to be used in a crawl space.

6 mil clear or black poly (heavy duty): used to cover crawl spaces and as a temporary cover for equipment and supplies. Also commonly used as a vapor barrier in between walls, under flooring, and under concrete slabs.

12 mil fiber-reinforced, virgin resin poly: great for crawl space vapor barriers or conditioned crawl spaces.

20 mil fiber-reinforced, virgin resin poly: great for conditioned crawl spaces and crawl space encapsulation.


Vapor BarrierMost non-crawl space companies that claim to offer vapor barrier installation cut corners and install a short term solution. Many will try to install the vapor barrier on top of an existing vapor barrier and debris. Also, many amatuers attempting to install vapor barriers fail to secure the poly to the ground leaving the plastic to pull away and leave exposed earth releasing moisture. We install the vapor barrier with great results for years to come!

When we install our vapor barrier, we always clean out all existing plastic and debris on the ground. Next, we roll out and tightly fit our 6-mil heavy duty plastic around and under obstacles and penetrations. Lastly, we secure the 6-mil poly to the ground using stainless steel 6 inch square stakes as well as a patented vapor barrier button that will not allow the plastic to tear before being pulled away

Related Topics:

     ➡ Crawl Space Encapsulation                                  ➡ Crawl Space Moisture Control

Prevent Crawl Space Flooding                             ➡ Crawl Space Dehumidifiers

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