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Indoor airPLUS

Indoor airPLUS Construction Specifications

Technical Guidance: Moisture Control

How to Use This Guidance


This “Moisture Control” Technical Guidance module was developed by EPA to support the Construction Specifications of the Agency’s indoor air quality (IAQ) labeling program for new homes, Indoor airPLUS. This program recognizes new homes equipped with a comprehensive set of features designed to reduce the risk of compromised air quality in new homes. Each module’s technical information supports the labeling program’s Construction Specifications. The technical guidance is intended to assist home builders, energy raters, and other housing professionals in implementing the specifications.

While this module presents significant details regarding installation methods and materials related to each specification, the guidance most importantly presents a principle that should be achieved in order to control a pollutant risk. For example, the principle may be to establish a drainage plane in the exterior walls to prevent rain from penetrating the wall system. While the guidance illustrates several approaches to establishing the drainage plane, it is not practical to attempt to capture every method and material that will meet the specification.

Please see: Introduction to Technical Guidance where "Required" and "Best Practice" installation procedures are explained, as well as the application of the Map of Climate Zones.

Although this guidance is designed to help protect IAQ in new homes compared with homes built to minimum code, it alone cannot address all IAQ problems. Occupant behavior is also important. For example, smoking indoors would negatively affect IAQ and the performance of the specified Indoor airPLUS measures.


This module describes construction methods and component materials for new homes to manage water from exterior and interior sources. For potential exterior sources, the discussions are divided into: 1. foundations; 2. exterior walls; and, 3. roofing systems.

It is important to keep liquid water out of foundations (including basements, crawl spaces, and concrete slabs), exterior wall systems, and roof/attic areas. Water that enters a home can result in serious damage to the structure caused by wood-decaying fungi growing on building materials, such as framing members, sheathing and window and door units. From an air quality perspective, water that wets susceptible building materials and furnishings can also promote the growth of mold that can make the home's occupants sick, and moist environments provide an attractive environment for insect pests.

ENERGY STAR Enclosure System Rater requirements are part of the moisture control strategy described in the EPA Indoor airPLUS specifications. These requirements help conserve energy by helping control air and thermal flows through building assemblies. However, controlling these flows is also critical to the effective management of water vapor migration and condensation. Since compliance and verification are required for ENERGY STAR certification, Thermal Enclosure System Rater Checklist requirements are not re-stated in these specifications. Read about the technical information for addressing the thermal enclosure.

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Terms Used in the Construction Specifications

The technical discussion of each IAQ issue in the module is preceded by the IAQ labeling program specification it supports. Specific terminology is sometimes included in a specification that relates to its application.

  • Exceptions to the requirements described in these construction specifications are noted as appropriate. For climate exceptions, refer to the International Energy Conservation Code (IECC) Climate Zone map (Figure 301.1). Climate Zone names may include a number for the temperature zone and a letter for the moisture zone (e.g. Zone 3C refers to coastal California only).
  • Notes provide additional information to clarify specification requirements.
  • Advisories provide additional guidance to be considered, but are not specification requirements.
  • Abbreviations and References used in the specifications are listed at the end of the specifications document.
  • Performance Test Alternatives describe alternate compliance approaches where performance testing is practical and results are comparable to those of the prescriptive best practices required in the specifications.

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The U.S. Environmental Protection Agency (EPA) strives to provide accurate, complete, and useful information. However, neither EPA nor any person contributing to the preparation of this guidance makes any warranty, express or implied, with respect to the usefulness or effectiveness of any information, method, or process disclosed in this material. Nor does EPA assume any liability for the use of, or for damages arising from the use of, any information, method or process disclosed in this document. Mention of firms, trade names or commercial products in this document does not constitute endorsement or recommendation for use.

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The Technical Guidance for the Moisture Module was developed by David Price of EPA’s Indoor Environments Division, Office of Air and Radiation, and Terry Brennan of Camroden Associates; illustrations were provided by Dennis Livingston of Community Resources. Project management, editing and other support were provided by The Cadmus Group, Inc., a contractor to the U.S. EPA. Initial drafts were provided by the National Center for Healthy Housing.

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