Let's take a look now at the steps to encapsulating a crawl space. Sealing the ground, foundation walls, piers, and vents is not as easy as it may at first seem. Using the correct materials, methods, and tools makes a big difference in the final result. Most of the photos on these pages are from a crawl space in Atlanta that was encapsulated in 2008.
Step 1. Determine if the crawl space can be encapsulated in its current form. If not, either make any changes needed to prepare it for sealing, or do not encapsulate. Encapsulating a crawl space can create new problems if it's not done correctly, so in some cases, a crawl space should not be encapsulated. Two big issues that must be looked at carefully are bulk water problems and the possibility of backdrafting combustion appliances in the crawl space. Pest control also places some restrictions on the details of encapsulation.
You can still seal a crawl space that has bulk water problems or atmospheric combustion appliances - but only after eliminating the water problem and replacing the atmospheric combustion appliances with sealed combustion or non-combustion (i.e., electric) models. With water problems, most of the time the source is bad drainage outside, so that must be addressed. Sometimes you need to install a perimeter drain and sump pump in the crawl space.
For the best info available on this topic, go to Advanced Energy's website and download their guidelines, titled "Closed Crawl Spaces: An Introduction for the Southeast." Crawl space encapsulation is not suitable as a DIY project in most cases, so learn what you can and then call in a professional.
The photo shows the Atlanta crawl space before being encapsulated. This ground had about 75% coverage with a 6 mil polyethylene vapor barrier and was also connected to a mechanical room and finished basement. The homeowners had tried numerous techniques and products to reduce the smells and humidity in the basement, to little effect. They also had very cold floors in winter since there was no insulation in the floor.
The only bulk water problem here was the result of a lazy HVAC contractor who ran the AC condensate line out of the mechanical room and into a corner of the crawl space. The encapsulation company installed a condensate pump and ran the drain all the way outside, which is what the HVAC contractor should have done to begin with. No combustion equipment in the crawl space meant no possibility of backdrafting when the crawl space vents were sealed up.