1.1 本规程概述了需要考虑的因素，描述了水蒸汽缓凝剂选择的设计原则和程序，并定义了适用于既定标准的水蒸汽传输值。本规范旨在指导设计工程师编制蒸汽缓凝剂应用规范，以控制通过隔热层的水蒸汽流量。它涵盖商业和住宅建筑施工和工业应用，工作温度范围为 −40至 +150°F(−40至 +66°C）。 重点是通过选择系统中最合适的组件来控制水分渗透。 1.2 以英寸-磅为单位的数值应视为标准值。括号中给出的值是到国际单位制的数学转换，仅供参考，不被视为标准值。 1.3 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.4 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 4.1 经验表明，不受控制的水进入隔热层是导致性能受损的最严重因素。水进入绝缘系统的方式有几种，主要有水蒸气扩散、携带水蒸气的空气泄漏和地表水泄漏。 在环境露点温度以下运行的绝缘系统的应用规范必须包括足够的蒸汽缓凝剂系统。蒸汽缓凝剂系统是独立的，不同于绝缘材料，或者由绝缘材料本身提供，前提是其具有足够的耐蒸汽性能，并且所有接头都密封以防水汽侵入，在这种情况下，不需要单独的蒸汽缓凝剂系统。为了选择适当的缓速器系统来控制蒸汽扩散，有必要制定可接受的实践和标准。 4.2 蒸汽减速器功能- 蒸汽缓凝剂的主要功能是控制扩散水蒸汽进入或通过渗透绝缘系统的运动。在某些情况下，蒸汽缓凝剂系统旨在防止地表水进入。当作为蒸汽缓速器正常工作时，它也将成为空气泄漏的屏障。 4.3 蒸汽缓凝剂性能- 缓凝剂的设计选择将受到缓凝剂材料的厚度、应用的基材、接头数量、板材的可用长度和宽度、系统的使用寿命和检查程序的影响。 这些因素中的每一个都会对缓速器系统性能产生影响，设计者必须考虑和评估每一个因素。 4.3.1 尽管本规程正确地将重点放在选择最佳蒸汽缓速器上，但必须认识到，错误安装可能会影响蒸汽缓速器的性能。在选择缓速器材料时，必须考虑安装或应用技术在获得设计水蒸汽渗透（WVP）性能方面的有效性。 4.3.2 指定“安装时”磁导率值是不切实际的，因为由于现场应用的性质，假设不可能达到与蒸汽缓凝剂材料本身等效的系统磁导率。最好的方法是指定适当的蒸汽缓凝剂，并确保遵循正确的安装和密封程序。

1.1 This practice outlines factors to be considered, describes design principles and procedures for water vapor retarder selection, and defines water vapor transmission values appropriate for established criteria. It is intended for the guidance of design engineers in preparing vapor retarder application specifications for control of water vapor flow through thermal insulation. It covers commercial and residential building construction and industrial applications in the service temperature range from −40 to +150°F (−40 to +66°C). Emphasis is placed on the control of moisture penetration by choice of the most suitable components of the system. 1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 4.1 Experience has shown that uncontrolled water entry into thermal insulation is the most serious factor causing impaired performance. Several ways exist by which water enters into an insulation system, the primary ones being diffusion of water vapor, air leakage carrying water vapor, and leakage of surface water. Application specifications for insulation systems that operate below ambient dew-point temperatures necessarily include an adequate vapor retarder system. A vapor retarder system is separate and distinct from the insulation, or is provided by the insulation itself when it is has adequate vapor resistant properties and all joints are sealed against water vapor intrusion, in which case a separate vapor retarder system is not necessary. For selection of adequate retarder systems to control vapor diffusion, it is necessary to establish acceptable practices and standards. 4.2 Vapor Retarder Function— The primary function of a vapor retarder is to control movement of diffusing water vapor into or through a permeable insulation system. The vapor retarder system in some cases is designed to prevent entry of surface water. When properly functioning as a vapor retarder, it will also serve as a barrier to air leakage. 4.3 Vapor Retarder Performance— Design choice of retarders will be affected by thickness of retarder materials, substrate to which applied, the number of joints, available length and width of sheet materials, useful life of the system, and inspection procedures. Each of these factors will have an effect on the retarder system performance and each must be considered and evaluated by the designer. 4.3.1 Although this practice properly places major emphasis on selecting the best vapor retarders, it must be recognized that faulty installation is likely to impair vapor retarder performance. The effectiveness of installation or application techniques in obtaining design water vapor permeance (WVP) performance must be considered in the selection of retarder materials. 4.3.2 It is impractical to specify an “as installed” permeance value because, due to the nature of field application, attainment of system permeance equivalent to the vapor retarder materials themselves is assumed not possible. The best approach is to specify an appropriate vapor retarder and insure that proper installation and sealing procedures are followed.