Crawlspace FAQ’s

What are the minimum standards for a weatherized crawl space?
6 mil vapor barrier covering all of soil of the crawl space floor (100% coverage) and extending up the perimeter walls and sides of the columns/piers 6 to 8 inches (mechanically or permanently sealed); air sealed floor of the residence at all penetrations (plumbing, electrical, and mechanical); R-19 floor insulation in place; foundation vents operational and/or sealed; and seams of the vapor barrier sealed.

What are the benefits of a closed crawl space?
Closing a crawlspace (which includes sealing the vents, insulating the walls, creating a vapor barrier and conditioning the air in the boundaries of the crawlspace) is now the standard for LEED homes, NAHB Green homes and various others rating systems that are recently being integrated into statewide building codes. The latest studies on crawl space ventilation indicate that ventilation (open crawl space) is actually contributing to moisture and humidity in the crawl space. Some of the benefits of a closed crawl space include:

  • Stay dryer than vented/open crawl spaces
  • Protect pipes from freezing
  • Require less insulation than open-air/vented crawl spaces (since the area of the perimeter walls is less than the area of the crawl space ceiling)
  • Bring ducts within the conditioned envelope of the home — an improvement that usually results in energy savings compared to vented crawl spaces.

According to researchers who conducted a careful study of vented and unvented crawl spaces in North Carolina, homes with sealed crawl spaces with insulated foundation walls use 18% less energy for heating and cooling than identical homes with open/vented crawl spaces with insulation between the floor joists.

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Why should I worry about the humidity levels in my crawl space?
Closed crawl spaces can maintain relative humidity below the 70% target and dramatically reduce the potential for condensation on surfaces in the crawl space. Crawl spaces should be sealed, insulated, and passively kept warm if mechanical equipment, ducts and plumbing are left there. A crawl space is less likely to have moisture problems if the crawl space floor is higher than the exterior grade. Moisture control provided by a closed crawl space can dramatically reduce the risk and associated liability of mold and moisture damage in the southeastern climate.

Are crawl space contractors licensed in the state of NC?
No, but there are specific standards that all crawl space contractors should follow. There are also certain certification programs in place, such as the Crawl Space Encapsulation Specialist certification by Therma-Stor or the Santa Fe Certification Contractor training tutorial.

What does “drain to daylight mean”?
Foundation, perimeter, or “footing drains” keep basements and crawl spaces dry from the outside weather conditions. “Draining to daylight” is a relatively new addition to building codes, for an extended time they were tied into the sewer system. Draining to daylight is the water that flows via gravity or pump to a drain on the outside (daylight) somewhere. Often foundation perimeter drains and downspouts must drain out onto the surface and not something underground like a sewer or septic system. Condensation from humidity or collective moisture can pool in a crawl space, and with the help of foundation drains, this water is extracted into the exterior of the crawl space. If the slope of the building site allows, foundation drains should connect to solid pipe that runs to daylight. The solid pipe should be sloped at a minimum pitch of 1/4 inch per foot, although a steeper slope is better. If there is more than 200 linear feet of foundation, add a second outlet or increase the size of the outlet pipe from 4 inches to 6 inches. When there isn’t enough area on the lot, the exterior drains should be connected to a sump pump in the crawl space via a 6-inch line that penetrates the footing near the sump location.

Will I void my termite contract if I close my crawl space?
Most PCOs (pest control operator) will offer a renewal or additional inspections for a specified period of time at an additional cost. These agreements may indicate re-treatment or damage repair. Such agreements, sometimes referred to as a contract or warranty, are not an assurance that termites will not return, but provide for corrective action to be taken as specified in the agreement. The purpose of periodic inspections following an initial treatment is to determine whether the treatment was effective and if termites are present inside the treatment barrier. Follow-up inspections are limited to all visible or accessible areas, including crawl spaces, and should be conducted as indicated in the agreement issued by the PCO.

Where can I find out more information on NC Building Codes for crawl spaces?
The North Carolina Building Code Council adopted the new crawl space code language in September 2004 and the state of North Carolina approved it in November of 2004. In some cases, local code officials may require or accept a stamped letter of approval from a registered professional engineer as an alternate path for permitting and inspection.
Some key additions to the updated code on closed crawl spaces include:

  • The crawl space shall be separated from adjoining basements, porches, and garages by permanent walls. All utility penetrations shall be sealed.
  • A minimum 6-mil polyethylene vapor retarder or equivalent shall cover 100% of exposed earth in the crawl space, with joints lapped at least 12 inches (305 mm)
  • Closed crawl spaces used as supply or return air plenums for distribution of heated or cooled air shall comply with the requirements of the N.C. Mechanical Code. Crawl space plenums shall not contain plumbing cleanouts, gas lines or other prohibited components. Foam plastic insulation located in a crawl space plenum shall be protected against ignition by an approved thermal barrier.
  • The thermal insulation in a closed crawl space may be located in the floor system or at the exterior walls, with the exception that insulation shall be placed at the walls when the closed crawl space is designed to be an intentionally heated or cooled, conditioned space.
  • At least one of the following methods of space moisture vapor control shall be provided, and combinations of multiple methods are allowed: Dehumidifier, Supply air, House air, Exhaust fan, Conditioned space

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Why are the quotes I am receiving so drastic in price? / What should I ask the contractor for when gathering quotes for closing my crawl space?
Most contractors are quoting their prices on square footage of the crawl space, physical installment, materials and resources used, if any drainage systems are required, and the evaluation of any damages or conditions the crawl space is in. Less expensive systems use a plastic liner of 6-mil (.006″), 8-mil, 10-mil or 12-mil thickness. More expensive systems use specially designed multi-layer 20-mil or 23-mil vapor barriers, and may also include a dehumidifier, a sump pump or drainage trenches.

Why are houses built with crawl spaces?
Over 76 million existing homes in the US are currently built on crawlspaces, and an upward 18% of all new homes in the US are being constructed with crawlspaces. Crawl spaces are inexpensive to build, functional in terms of providing a level foundation for flooring on sloping sites, and convenient spaces in which to locate plumbing, electrical lines, and ductwork for heating and air conditioning systems. There are basic structural benefits that are provided in the design of a crawl space that are functional for certain types of homes; for example, crawl spaces get a house up off the ground (anywhere from 1-4 feet), which is especially important when considering damp or termite-prone areas. Crawl spaces are also much more cost effective than basements, and very comparable in price to a slab.

Can I close my crawl space myself?
Yes, but we highly recommend referring to the crawl space contractor directory provided on HomeEnergyNC. If the costs of closing the crawl space falls under general contracting law (project costing less than $30,000) than a permit is not required. Although, certain additions and changes within the crawl space require a permit such as replacing HVAC, any electrical rewiring, addition of dehumidifier, etc. If there are any heating or natural gas appliances within the crawlspace, exhaust must be piped to the outdoors and requires a permit. For insulation, if your home has under-floor insulation than additional insulation within the foundation walls of the crawl space is not required. Check to see what insulation and other systems directly affect your crawl space.

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What questions should I be asking my Crawlspace Contractor? 

  • Ask for a clear outline of scope of work and how the items listed are addressing any problems.
  • Ask what kind of labor & material warranty the contractor offers.
  • Will the work be done according to NC code?
  • As needed the crawl space door is replaced; and in some situations a dehumidifier and/or a sump pump is installed. These “closing” systems can also be used in a basement with a dirt floor, one with uneven walls and floors, or one with a large rock or other unmovable object.
  • The crawl space floor should be cleaned (no rocks or other debris to rip the plastic) and graded. When installed, the encapsulation system should be completely airtight. All seams should be overlapped by at least a foot, and sealed shut with special tape. Every potential gap or seam should be sealed, as should any vents.
  • If possible, get estimates from several companies with specific information about the materials used and the work to be done. For example, some materials such as dehumidifiers and polyethylene plastics are more expensive than others but provide the same service.