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Your Crawlspace Crawl Space Encapsulation System

If you get three general contractors together and the discussion turns crawlspaces and moisture control and other crawlspace problems, you will probably hear six opinions. Folks, seem to have different and often conflicting opinions about what tack is the best to take. The idea of crawlspace encapsulation (sealing) has been around for a while now. Your Crawlspace Inc. has been sealing crawlspaces for a decade and follows the recommendations of Advanced Energy and the US Department of Energy. Here’s our take on the subject.

There has been much research on crawlspace encapsulation during the past decade. The US Environmental Protection Agency, the US Department of Energy, the ZEBRAlliance at Oak Ridge National Laboratories, and a research organization called Advanced Energy have all done excellent and groundbreaking research in the area of crawlspace encapsulation. Their research findings were instrumental in the last revision of the International Building Code and the recommendations of many state energy offices. They all agree in a few, very important areas.

When building scientists consider your home, they think of it as a single system. Your HVAC system, insulation, windows, attic, living space, and crawl space all work together. All of these building components need to be optimized and balanced to achieve maximum comfort, performance, and energy efficiency. Your crawlspace is an important part of this system.

Your house is like a giant chimney. By natural convection, air is drawn in through crawlspace vents and air leaks. Because warm air rises, the crawlspace air is drawn through the living space (along with mold spores, odors, and moisture) and exhausted through the attic. This phenomenon is called the “chimney effect” or “stack effect.” In the summer, your crawlspace is naturally cooler than the ambient outside temperature. So when the warm, humid outside air reaches the cooler crawlspace surface areas, the moisture condenses on framing, plumbing, wiring, insulation and especially HVAC ductwork and “sweats”, just like an iced tea glass sweats on your kitchen table in the summer. In the southeast it is not unheard of for crawlspace humidity to approach 100% and actually rain inside the crawlspace!

The moisture in your crawlspace creates an ideal environment for wood destroying organisms, mold, and mildew. It can saturate and destroy the effectiveness of your insulation and promote wood rot. And because of the chimney effect, the humid crawlspace air, full of mold and mildew spores and nasty odors, eventually finds its way into your living space creating an unhealthy environment and causing your air conditioning to work overtime to dehumidify the air. Just a vapor barrier might help a bit, but most of the moisture is coming from outside through your vents, not your dirt, crawlspace floor.

So, the alternative to a vented crawlspace is an encapsulated (sealed) crawlspace. Crawlspace encapsulation involves sealing all outside vents, installing a high-performance vapor retarder on all exposed wall and floor surfaces, insulating the walls and rim joist, and conditioning the air.

The prevailing research claims that by insulating the walls and rim joist, it is unnecessary to insulate the floor. However, if you have existing floor insulation and it is in good condition, leave it in place. We generally recommend spray foam or a rigid foam board insulation that is fire-retardant, low VOC, and offers an R-13 value or greater. Foam board cuts easily and can be used for sealing existing crawlspace vents too. The sill plate should be caulked and spray foam insulation or paper-faced fiberglass insulation is used to insulate the rim joist.

The building codes in most areas require the air in an encapsulated crawlspace to be conditioned. That generally means adding a dehumidifier or using the existing HVAC system to condition the air. The EPA and the Department of Energy recommend using the existing HVAC system at a rate of one cubic foot per minute of conditioned air per fifty square feet of crawlspace area. That’s a small fraction of the conditioned air it takes to condition a typical bedroom. A qualified HVAC contractor can add one or two 4” or 6” vents to a system for a nominal cost. The vents are usually equipped with a butterfly valve that can be adjusted to get the desired air flow.

An alternative to the installation of the vents is a crawlspace dehumidifier. Sometimes HVAC ducts are in the attic and a dehumidifier is the only choice. And sometimes humidity is such a major problem that it is necessary to add a dehumidifier and an HVAC baffle vent. A remote humidistat is inexpensive and an invaluable tool for determining the correct amount of dehumidification. Remember that you’re not trying to heat and cool your crawlspace; you’re just adding a small amount of conditioned air. A relative humidity target of 60% or lower is a good place to start. Mold and mildew will not grow below 60% relative humidity.

Your Crawlspace Inc. installs the Your Crawlspace Inc. vapor barrier system. It is the highest quality and safest system available. Your Crawlspace Inc. pioneered encapsulation in the southeast and sells innovative crawlspace products throughout North America. You can learn more about the system at their website, All of the experts agree that when you seal a crawlspace or add a high performance vapor barrier, the vapor barrier should be firmly attached and sealed to the crawlspace foundation wall. Most reputable crawlspace contractors use some sort of mechanical fastener to accomplish this. Even after being attached, the vapor barrier needs to be sealed the foundation. Some contractors use flammable and potentially explosive mastic. This approach is dangerous, labor intensive, and can even damage the foundation wall. We install the Your Crawlspace Inc. system because it is the safest system for our installers, the homeowner and their pets, and the home’s foundation.

In addition to dramatically increasing indoor air quality and protecting the structure of your home, several research studies from Advanced Energy indicate that crawlspace encapsulation can actually lower energy usage. These studies were done in several parts of the country with varying climates. 

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