Green Building    
Posted: September 1, 2014, 12:00am by Scott Allred

Closed Crawl

Most houses in this region of the country are built on a crawl space – an open area under the home that allows for grade changes, and room for plumbing and mechanical systems. To allow for ventilation of these crawl spaces, vents are installed through the walls to the outside. This allows for air circulation and to replace stale air with fresh air from the outside. This system is commonly referred to as a “vented crawl space”.

Recent studies have discovered that foundation vents bring in more moisture than they let out. A new type of crawl space system, known as a Closed Crawl Space, has no vents to the outside, and can provide greatly improved moisture control and significant energy savings.
Excessive moisture in a vented crawl space is the primary cause associated with a host of serious crawl space concerns.  It is estimated that 60% of the air you breathe on the ground floor of a vented crawl space home comes from the crawl space! Some of the common symptoms of excessive crawl space moisture are:

• Mold or moisture damage in the crawl space or living area.
• Musty odors in the living area and closets.
• Family members are suffering from allergies, asthma, or headaches.
• Condensation ("sweating") on air conditioning ductwork or equipment.
• High humidity in the crawlspace and living area which can be seen as mold growth on surfaces.
• Condensation on insulation, water pipes or metal (rust) in the crawl space.
• Buckling hardwood floors.
• Doors and windows that stick due to swelling.
• Insect infestations such as termites and wood-boring beetles.
• Mold leading to rot in wooden framing members.

When warm, moist outside air enters a crawl space, it instantly cools and drastically increases the relative humidity of the crawl space. When the relative humidity goes over 100 percent, the moisture is released into the crawl space atmosphere, with condensation accumulating on the walls, floors and building components. Moisture can pass from a crawl space into a building through cracks in walls, floors, and ceilings. This movement of air is known as “stack effect” a natural phenomenon of constant movement of air through the house. Here's how it works in crawl spaces: When hot air rises, most of it finds ways to escape into the upper areas of a house and then outside. As the hot air leaves the building, cool air rushes in through leaky windows, doors and crawl space vents to replace it and repeat the cycle. The air in the crawl space that gets sucked up into the living area brings with it moisture, dust, allergens, mold spores and radon. If the stack effect is causing air to be drawn into the house through the lower levels, then any possibility of meaningful cross-ventilation, allowing moist air to leave through the vents, is negated.

According to Billy Tesh, owner of CrawlSpace Care, a Greensboro based business that specializes in closed crawl space installation; two factors have led to moisture problems in crawl spaces:

Air Conditioning: The advent of central air conditioning in the 1980’s created a larger difference in the temperature between the inside of the house and the crawl space.  Without air conditioning, the ambient temperature inside a home was about the same as in the crawl space. This did not lead to condensation in the crawl space. Since early air conditioning systems were not very efficient, most people did not experience major problems. Newer high-efficiency models, coupled with tighter building construction, have magnified the temperature difference that has led to many of the moisture problems today.

Waterproofing: In our area, waterproofing of foundations was not made a standard practice until 1985. As a result, many homes have moisture present in the crawl spaces due to poor grading, malfunctioning gutter systems (or no gutter system), and leaks from plumbing and waste systems. Most of these problems can be repaired with interior drains, downspout piping, waterproofing systems, and proper grading around the house.

So how do you “close” the crawlspace? There are two primary closed crawl space methods: the wall insulated system and floor insulated system. In new construction and retrofit of existing homes where there is no floor insulation, the system includes closing and sealing the foundation vents, sealing around all plumbing, HVAC, and electrical penetrations, and installing a thick moisture barrier on the exterior walls and around all piers. Finally, rigid foam insulation is installed on the exterior walls of the crawl space (verses in the floor joist). A supply duct from the existing HVAC system is installed to allow for conditioned air to flow into the crawl space. This reduces humidity and the temperature difference between the home and the crawl space.

In retrofits, where floor insulation is already installed, the installation method is essentially the same.  The exception is that the existing insulation is left in place in the floor joists and the exterior walls are not insulated.

One word of caution here - if the crawl space houses an appliance such as a gas or oil furnace or gas hot water heater, the appliance in most cases needs make-up air for combustion. Additional provisions will need to be made to accommodate these issues.


Energy Savings and Costs: The cost to install a closed crawl space system in new construction will cost approximately $2.50 – $2.75 per square foot of crawl space area. To retrofit an existing home, expect to spend approximately $3.00 to $3.50 per square foot of crawl space area. According to Billy Tesh, the cost to close the crawl space of an average sized home will range from $2,000 to $3,000.

In addition to virtually eliminating stack effect and improving the quality of your indoor air, significant savings on energy bills can be expected. In new construction, studies from Advanced Energy, a non-profit founded by the N.C. Utilities Commission to investigate and implement new technologies for energy efficiency, found that a closed crawl space can lead to energy savings of 15 – 18%. For additional information on the Advanced Energy studies, please visit

For existing homes, the energy savings can be considerably higher – up to 50% in some cases! Many older homes do not have any insulation in the crawl space at all. By insulating and closing the crawl space, the load on the HVAC system is reduced. Additionally, the stack effect in an older home can be significantly higher because the home has more leaks and places for air to enter.

In conclusion, research confirms that closing the crawl space can greatly improved moisture control and result in significant energy savings to the homeowner. In addition, indoor air quality can be improved by reducing or eliminating “stack effect”.

For additional information on closed crawl spaces, please visit

Scott Allred is chairman of the Triad Green Building Council and the owner of Precept Construction. He can be reached at or 286-6811. For additional resources on green building, visit
The Triad Green Building Council serves members of the Greensboro, High Point, Winston-Salem and Burlington Home Builders Associations that are interested in learning more about green building techniques, products and services.
The council meets monthly with an educational program as the primary focus. Additional seminars and workshops are offered throughout the year for industry professionals and consumers. To find out more about the Triad Green Building Council, contact the Greensboro Builders Association at 855-6255 or

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