Home Innovation Insights

Thomas Kenney, PE
May 23, 2013

The Modern Crawlspace: No Rot, Mold, or Bugs About It!

Historically, the conventional wisdom on venting crawlspaces has ranged from keeping the passive vents open at all times, to keeping them closed at all times, to keeping them open except for during the heating season to save on heating expenses. Nothing like having options ... and lots of confusion to go along with them!

Depending on local conditions, venting can keep a crawlspace dry. In fact, until recently building codes mandated crawlspace vents in homes. However, outdoor air in hot-humid climate zones can be a source of moisture for a vented crawlspace that can foster conditions prime for infestation of bugs, mold, and rot. Today there is a better option available to the vented crawlspace, expecially for hot-humid climates. The International Residential Building Code (IRC-2012, Section R408.3) now permits unvented crawlspaces.

The IRC requires an unvented crawlspace to:

  • have ground cover that is a Class I vapor retarder that has sealed seams and extends up onto the stem wall where it is sealed and attached to the wall or the wall’s insulation when present
  • be conditioned at a rate of 20 CFM/1,000 square feet of crawlspace area. Continuous exhaust ventilation is permitted, as is conditioned-air supply. An air pathway to a common area is required for providing relief for the mechanically vented air.

Unvented crawlspaces are dry, energy-efficient, functional, and a practical option for single-family new construction. Since they are a relatively new construction practice, Home Innovation Research Labs and the Southern Forest Products Association created educational materials specifically designed for builders and trades. The resources include a downloadable TechSpec and a four-part instructional video series – all are available online at no cost.

The TechSpec, “Closed Crawlspaces: Making the Transition,” is an easy-to-read summary of the technology that addresses its benefits and key steps when transitioning from more traditional slab-on-grade or conventional vented crawlspace construction. As highlighted in the TechSpec, benefits of a closed crawlspace include:

  • Dryness and durability as a result of the insulation, air sealing, moisture control measures, and conditioned air in a closed crawlspace.
  • Marketability to homebuyers – raised wood floor homes provide architectural appeal and a warm and comfortable walking surface that can be marketed to prospective buyers.
  • Applicability for sloped and infill sites, and challenging soil conditions.
  • Simplified scheduling of trades and inspections.
  • Improved whole-house energy efficiency – closed crawlspace temperatures are more stable compared to an attic or a vented crawlspace, and locating ducts and mechanical equipment in the space reduces heating and cooling loads.
  • Simplified installation of mechanical systems – provides access for installation and maintenance of plumbing and mechanical systems, and allows for changes to floor plans.
  • Limited learning curve for trades due to the use of familiar materials and methods.

In addition to discussing the benefits, the “Making the Transition” TechSpec addresses code considerations, best practices, foundation walls, height and access, wood floor framing, moisture management, air sealing, insulation, and mechanical systems. The information presented is consistent with the provisions of the 2012 IRC, and is focused on warm and mixed-humid climate regions in the southeast (Climate Zones 3A and 4A).

Beyond the summary information in the TechSpec, this new bundle of educational resources also includes a series of four instructional videos online that walk builders through the various stages of closed crawlspace construction and address specific hot spots in greater detail. The four videos are:

  • How to Build a Closed Crawlspace in Climate Zones 3A and 4A
  • Hot Spot: Closed Crawlspace – Sealing the Ground Vapor Retarder to the Wall
  • Hot Spot: Closed Crawlspace – Installing Wall Insulation
  • Hot Spot: Closed Crawlspace – Ventilation

Builder resources like this can be invaluable in helping to get new construction practices and technologies into the mainstream. Home Innovation often helps industry groups, trade associations, and government agencies create TechSpecs, Builder Guides, and other similar resources to eliminate some of the barriers to technology adoption that may exist.

If you're interested in finding out more about the resources like this we've previously created, or want to explore the possibility of having us create one for your product or industry segment, give me a call at 800.638.8556.

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