I’ve done a whole lot of research on sealed crawlspaces the past few weeks. I have read everything from product literature provided by contractors who install the systems, to building science articles, to ASHRAE standards and studies. Here are a few of the highlights of what I have learned:

What is a Sealed Crawlspace?

A sealed crawlspace is also referred to as closed, conditioned, or semi-conditioned. The basic design has no vents, insulated foundation walls, a heavy plastic and/or concrete liner on the floor, and an insulated and weather-stripped access door.

A small amount of conditioned air is delivered to the crawlspace area from the HVAC system creating positive pressure in the crawlspace. The positive pressure prevents air from the crawlspace being drawn into the duct work and delivered to the living space. Crawlspace air remains in the crawl not in the living areas.

What are Some of the Benefits Claimed?

Sealed crawl space systems are said to reduce or eliminate many common problems, such as:

• Mold or moisture damage in the crawl space or living area
• Musty odors
• Condensation (“sweating”) on air conditioning ductwork or equipment
• Condensation on insulation, water pipes, or truss plates in the crawl space
• Buckled hardwood floors
• High humidity throughout the house
• Insect infestations
• Rotting of wooden framing
• Increased load on air conditioning and dehumidification systems

Many studies I read documented average energy savings from 15-18%. Another resource also pointed out that many of the crawlspace upgrades qualify for the 15% federal tax credit energy program.

The two most common disadvantages I came across were the cost and the ability to retrofit existing crawlspaces.

Are Vented Crawlspaces Really a Problem?

There was a study performed by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) involving fungal sampling indoors, outdoors, and in the crawlspaces of 45 homes with traditionally designed vented crawlspace. Air leakage testing determined the connections between the house, crawlspace, and HVAC systems located in the crawlspace.

Results indicated that most of the crawlspaces contained liquid water, moisture vapor, and fungal spores. The houses also contained measurable holes between the crawlspace and the living space, with both natural and mechanical air movements across these openings.

This led to a measured transmission of fungal spores from the crawlspace to the living area. High moisture levels in vented crawlspaces in the Southeastern United States were linked to higher mold counts inside the living space.

There are also a number of excellent scientific articles available on www.BuildingScience.com that explain why traditional vented crawlspace designs may not be the best option for humid climates.

Want More Information?

Advanced Energy is an independent non-profit corporation that is governed by a Board of Directors appointed by the governor of North Carolina and the member utilities. The company was set up and still operates to work with member utilities on energy efficiency and conservation projects. There is a lot of useful information regarding crawlspaces and other topics in the knowledge library of their website at:

http://www.crawlspaces.org/

Air Matters LLC has performed mold testing services in the Raleigh NC area since 2002. The owner, Renee D. Ward, has over 25 years of safety and environmental experience and holds both her Bachelors and Masters degrees in engineering. Renee is also a member of the American Industrial Hygiene Association and the Indoor Air Quality Association. You may contact Air Matters at (919) 961-2221 or info@AirMattersMoldTesting.com.