DESIGNING CLOSED CRAWL SPACES - Advanced …

1 Moisture Management A roof runoff system to direct water awayfrom the house Site grading and landscaping that directsground surface water away from the house Foundation drains and foundation damp-proofing or water-proofing to protect thestructure from sub-surface water Air sealing of the access door, perimeter walland perimeter framing to prevent the entry ofmoisture-laden outside air and to separate thecrawl space from areas under porches or decks An access door that is protected from roofrunoff, at least 4" higher than the exteriorsoil grade and made of a non-corrodingmaterial, especially in coastal communities A fully sealed vapor retarder on the floor andperimeter walls to reduce evaporation ofwater into the CRAWL space Appliance discharge pipes and exhaustsfrom kitchens, bathrooms and clothes dryersthat terminate outside the CRAWL space A mechanical drying system to reducehumidity (for example, a supply ofconditioned air or a dehumidifier)

2 Drains with backflow valves or sump pumpsto remove liquid water from the CRAWL spaceif necessary Flood vents that minimize standby airleakage, when requiredPest Control A termite inspection gap at the top of theperimeter wall to facilitate detection Batt insulation in the band joist area of wall-insulated CLOSED CRAWL SPACES to facilitateinspection or treatmentCombustion Safety Specification of direct-vent ( two-pipe )combustion appliances to ensure adequatecombustion air for fuel-fired appliances, ifapplicable. Some manufacturers have direct-vent cabinets for use with non-direct-ventmodels. Alternate means of providingcombustion air must be approved by theappliance manufacturer and local residentialcode requirements.

3 For homes on slabs, basements or crawlspaces, specification of carbon monoxidemonitors or alarms if the structure has an attached garage or any combustionappliances For homes on basements or CRAWL SPACES ,optional specification of an appropriatelyplaced raw-gas leak alarm if fuel-firedappliances or fuel lines are in the homeFire Safety Air sealing of all penetrations in the sub-floor with non-porous materials Documentation of fire-rating to allowinstallation of exposed foam insulationwithout a thermal barrier, if applicable Documentation of fire-rating to allowinstallation of exposed facing or backingmaterials on batt insulation, if applicableThermal Insulation Insulation at the sub-floor or at the perimeterwall to provide the R-value required by thelocal residential code.

4 Note that perimeterinsulation may be located on the interiorsurface, exterior surface or inside theperimeter wall, or the perimeter wall itselfmay provide the required R-value Insulation at the sub-floor installed withoutgaps or compression and in full contact withthe sub-floor to achieve nominal R-value Non-porous insulation if the perimeter wallis insulated Insulation on the CRAWL space access(es) ofminimum R-2 Radon Control In areas where radon is a risk or where thelocal residential code requires control ofradon or other soil gases, houses withclosed CRAWL space foundations can betested, monitored and, if necessary,mitigated with the same techniques used forhouses with a slab or basement foundationin the same region.

5 The Environmental Protection Agencyand the Surgeon General recommend testingall homes for radonA quick reference on CLOSED CRAWL StartedBoth scientific research projects and real-worldinstallations demonstrate that properly CLOSED crawlspaces can provide much better moisture control thanconventional,wall-vented CRAWL SPACES in temperate-humid climates. Homes with CLOSED CRAWL SPACES (often also called sealed, unvented or conditioned CRAWL SPACES ) also can savesignificantly on energy when compared to homes withwall-vented CRAWL SPACES . This sheet summarizes key issues that builders, codeofficials and consumers should keep in mind whendeciding how to design or install CLOSED CRAWL spacesin new construction.

6 The second sheet provides two sample designs thathave been field-tested and extensively monitored. For more details and information on improving wall-vented CRAWL SPACES in existing homes, CLOSED CRAWL SPACESThe recommended components of a good design fall into six major categories:HIGH-PERFORMANCE Strategies for Avoiding ProblemsQuality installers of CLOSED CRAWL SPACES knowthat managing moisture during the process ofconstruction is critical for success and will useseveral strategies to avoid problems: Grading the CRAWL space floor surface to oneor more low spots and installing a drain orother method to remove water that enters thecrawl space prior to dry-in Grading around the foundation as soon aspossible to reduce the amount of roof runoffor ground surface water that enters the crawlspace Minimizing the amount of rainwater that canenter the CRAWL space Covering the CRAWL space floor with atemporary vapor retarder by the time thestructure is dried-in.

7 This temporary covermust be removed before installation of thefinished ground vapor retarder. Puncturing holes at low spots in thetemporary ground vapor retarder (if the groundis not saturated) to allow small puddles todrain into the ground Closing the access door(s) and running adehumidifier to remove accumulated moistureafter the structure is dried-in Coordinating with the construction site crew toensure that the CRAWL space door is CLOSED asmuch as possible, that all drains remainunblocked and that any dehumidifiers have apower source, run long enough to provide thenecessary drying and are protected from theftAdditional Recommendations Coordinate with your pest managementprofessional to ensure that the CLOSED CRAWL space system does not interfere withtheir treatment or affect their warranty, if applicable Mechanically fasten the liner material to theperimeter wall in addition to sealing it to thewall.

8 Adhesives, sealants or tapes alone maybe insufficient to support the material. Use duct mastic with embedded fiberglassmesh tape to seal seams in CRAWL space vaporretarder materials. If tapes or sealants are tobe used, ensure that the product is acceptedfor use by the manufacturer of the material and will provide long-term of the method, a quality installerwill have a process in place to ensure properinstallation. Protect 6-mil un-reinforced polyethyleneground vapor retarders to avoid damage inareas that will be accessed for servicing ofmechanical equipment. Thicker, reinforcedpolyethylene materials are more Assurance OptionsExperienced installers care about the long-termperformance of their system and will usuallyoffer one or more of the following qualityassurance options with their CLOSED CRAWL spacesystem.

9 A monitoring system to inform the homeownerof relative humidity levels in the CRAWL space A water alarm to inform the homeowner of abuildup of liquid water in the CRAWL space A posted sign informing anyone entering thecrawl space of the system componentsmaintaining the integrity of the system A repair kit for fixing small amounts ofdamage to the vapor retarder after the house is occupied An annual monitoring service to replacebatteries in monitoring systems and check thatthe CRAWL space system is in good workingorder. This may include measurements ofwood moisture content or air tightness, ordownload and analysis of data loggingequipment A guarantee that relative humidity will bemaintained below an agreed-upon target(typically 70% or lower) over specifiedperiods of time with exceptions for water leaksor intrusion outside their control References to independent third-parties forquality assuranceChoosing a design for a CLOSED CRAWL space goeshand-in-hand with the first steps required toinstall the CLOSED CRAWL space : coordinating withcode officials to ensure that your design meetslocal residential code requirements and obtainingthe required permits.

10 At the time of this writing,the North Carolina Building Code Council hasadopted and the state of North Carolina hasapproved new code language governing bothwall-vented and CLOSED CRAWL SPACES . This newcode is available for reference as of January 1,2005, as an alternate to the existing printed code,and the new code will be enforced in 2006 withthe release of the updated North CarolinaResidential Code. In some cases, local codeofficials may require or accept a stamped letter ofapproval from a registered professional engineeras an alternate path for permitting and installers ensure that their employees aretrained in the use of the tools and materialsrequired to install their CLOSED CRAWL spacesystem and generally provide and/or require theuse of respirators and protective clothing for thecomfort and safety of their employees.