1.1 本指南涵盖了屋顶外壳改造或内部环境变化对现有屋顶外壳造成的湿热影响的评估。可能影响湿热性能的改变的示例包括但不限于:绝缘材料的安装或改变、空气或蒸汽阻滞剂的安装、自然通风阁楼空间的通风口的改变或安装机械阁楼通风，或可能影响屋顶外壳的干燥潜力、通风、热性能或蒸汽阻力的任何其他改变。可能影响湿热性能的内部环境变化的示例包括但不限于:占用的变化、先前未调节空间的机械调节、在现有阁楼空间内增加可居住空间、或将影响现有屋顶平台下方的温度、相对湿度或气流的任何其他改变。1.2 本指南旨在解决现有屋顶围护结构改造的湿热影响，该围护结构最初包含自然通风或非空调阁楼或椽子空间。 1.3 本指南可用作评估的一部分，以评估影响现有屋顶围护结构下方结构的湿气相关问题的原因，这些结构遭受湿气积聚相关问题，包括对屋顶椽子、桁架和托梁的影响。 1.4 本指南不涉及屋顶覆盖材料的安装、维护或更换。 1.5 本指南不包括对现有屋顶围护结构进行结构评估的规定。屋顶荷载的变化，包括恒载和活载，需要在本指南的规定之外进行评估。1.6 本标准并不旨在解决与其使用相关的所有安全性问题（如果有）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践并确定法规限制的适用性。 1.7 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》中确立的国际公认的标准化原则制定的。 ======意义和用途====== 5.1 现有的或具有历史意义的建筑，或两者兼而有之，最初是用未隔热或未调节的屋顶围护结构建造的，或两者兼而有之。现有建筑物的翻新或改造，包括改变屋顶围护结构或改变阁楼或封闭椽子空间或屋顶围护结构下方的调节空间内的环境条件，可能会对屋顶围护结构的性能产生重大意外影响。如果没有适当的评估，屋顶外壳的热和湿度特性的变化或屋顶外壳下方空间的通风和调节的变化可能会产生严重的负面影响，特别是对现有结构的完整性以及冷凝和其他与水分积累相关的问题的可能性。本标准旨在就如何评估此类变更和变更提供指导。 5.1.1 通风改造- 每当屋顶外壳内的通风发生变化时，都应评估对屋顶平台、屋顶框架构件和屋顶覆盖材料的影响。一些屋顶外壳具有受保护的开口（例如拱腹通风口或屋脊通风口），专门用于沿着屋顶平台的下侧提供通风。然而，其他建筑物的建造并没有密闭的意图，其特征是通过屋顶平台、屋檐的建造中的空隙或固有间隙和接缝实现自然通风，以及不寻求提供密闭的建筑物外壳的建造技术。通过添加蒸汽阻滞剂、空气屏障或消除自然通风（例如，转换为不通风的阁楼或封闭的椽子空间）来减少或消除这些屋顶外壳的自然干燥潜力可能会导致湿气积聚或增加现有屋顶平台、阁楼空间或结构框架构件内的水分含量，这可能会导致结构退化或减少这些建筑部件的使用寿命。屋顶围护通风在控制湿气、湿气、温度和冷凝方面的作用和重要性在 附录X1 . 5.1.2 屋顶板正下方热阻的改变- 每当向屋顶外壳添加额外的隔热层时，特别是当添加到屋顶平台的下侧时，应评估对屋顶平台和结构框架构件的影响。许多古老的历史建筑的屋顶外壳几乎没有隔热层。用这些传统屋顶围护结构建造的现有和具有历史意义的建筑越来越多地涉及节能问题。如果没有适当的评估，这些屋顶外壳的热和湿度特性的变化可能会产生严重的负面影响。通过在屋顶平台下方添加隔热层来改变屋顶外壳的热梯度可能会产生意想不到的效果。绝热材料的添加减少了热流，并通过减少热流而对组件的干燥潜力产生负面影响。具体地，当将隔热层添加到屋顶板的下侧时，现有屋顶板和结构支撑的水分含量是值得关注的。尽管在甲板下侧安装绝缘材料可能会带来关于屋顶甲板或屋顶覆盖物的挑战或担忧（例如，当转换到不通风的阁楼条件或封闭的椽子空间时），但创造性的设计技术可以允许在甲板下添加绝缘材料，同时保持屋顶甲板正下方的通风空间。 5.1.3 阁楼或室内环境条件的改变-每当紧接屋顶围护结构下方或屋顶围护结构阁楼空间内的温度或相对湿度或两者发生变化时，应评估对屋顶平台和结构框架构件的影响。对于业主或设计师来说，通过增加现代暖通空调系统来升级现有建筑是一种常见的做法，同时试图防止阁楼的过度能量损失。一个共同的项目目标是使屋顶和阁楼空间在隔热和空气屏障方面达到当前的能源规范。此外，阁楼空间内机械设备、喷水灭火系统或其他专用设备的存在通常导致需要调节阁楼空间的部分或整个阁楼空间。这可能会对屋顶外壳的性能产生影响。5.1.4 蒸汽阻滞剂的添加- 将任何蒸汽不可渗透材料添加到原本蒸汽可渗透的屋顶外壳中都有可能改变整个屋顶外壳的湿热性能。这可能导致在添加任何不可渗透材料之前不会发生的水分的意外积聚，无论该材料是否旨在起到蒸汽阻滞剂的作用。

1.1 This guide covers the evaluation of hygrothermal impacts to existing roof enclosures resulting from roof enclosure alterations or changes to the interior environment. Examples of alterations that may affect the hygrothermal performance include but may not be limited to: installation of or alterations to insulation, installation of air or vapor retarders, alterations to the ventilation openings of naturally ventilated attic space or installing mechanical attic ventilation, or any other alterations that could impact the drying potential, ventilation, thermal performance, or vapor resistance of the roof enclosure. Examples of interior environment changes that may affect the hygrothermal performance include but are not limited to: changes in occupancy, mechanical conditioning of a previously unconditioned space, adding habitable space within an existing attic space, or any other alteration that will impact the temperature, relative humidity, or air flow beneath the existing roof deck. 1.2 This guide is intended to address the hygrothermal impacts of a retrofit to an existing roof enclosure which originally contained naturally ventilated or unconditioned attic or rafter spaces. 1.3 This guide can be used as a part of an evaluation to assess the cause of moisture-related issues impacting the structure beneath an existing roof enclosure suffering from moisture accumulation related issues, including impacts on roof rafters, trusses, and joists. 1.4 This guide is not intended to address the installation, maintenance, or replacement of roof covering materials. 1.5 This guide does not include provisions for structural evaluation of the existing roof enclosure. Changes to the roof loads, including dead and live loads, need to be evaluated outside of the provisions of this guide. 1.6 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. 1.7 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 ====== 5.1 Energy conservation is being addressed more often on existing or historically significant buildings, or both, originally constructed with uninsulated or unconditioned roof enclosures, or both. Renovations or retrofits of existing buildings that include altering the roof enclosure or changing the ambient conditions within the attic or enclosed rafter space(s) or conditioned spaces below the roof enclosure can have major unintended impacts on the performance of the roof enclosure. Without proper evaluation, changes to the thermal and moisture properties of the roof enclosure or changes to the ventilation and conditioning of the space below the roof enclosure could have serious negative impacts, particularly on the integrity of the existing structure, and the potential for condensation and other moisture accumulation related issues. This standard seeks to provide guidance on how to evaluate such changes and alterations. 5.1.1 Alterations to Ventilation— Any time the ventilation within a roof enclosure is altered, the impact on the roof deck, roof framing members, and roof covering materials should be assessed. Some roof enclosures have protected openings (such as soffit vents or ridge vents) specifically intended to provide ventilation along the underside of the roof deck. However, other buildings have been constructed with no intent to be airtight and featured natural ventilation achieved through voids or the inherent gaps and seams in the construction of the roof deck, eaves, and construction techniques which did not seek to provide an airtight building enclosure. Reducing or eliminating the natural drying potential of these roof enclosures by adding vapor retarders, air barriers, or eliminating natural ventilation (for example, converting to an unvented attic or to enclosed rafter spaces) may lead to accumulation of moisture vapor or increase the moisture content within the existing roof decks, attic spaces, or structural framing members, which could cause structural degradation or reduce the service life of these building components. The role and importance of roof enclosure ventilation in managing moisture, moisture vapor, temperature, and condensation is discussed in Appendix X1 . 5.1.2 Alterations to Thermal Resistance Directly Below the Roof Deck— Any time additional insulation is added to a roof enclosure, particularly when added to the underside of the roof deck, the impacts on the roof deck and structural framing members should be assessed. Many older and historic buildings feature roof enclosures that have little to no existing insulation. Energy conservation is being addressed more often on existing and historically significant buildings constructed with these traditional roof enclosures. Without proper evaluation, changes to the thermal and moisture properties of these roof enclosures could have serious negative impacts. Altering the thermal gradient across the roof enclosure by adding insulation below the roof deck can have unintended effects. Addition of thermal insulation reduces heat flow and negatively impacts the drying potential of the assemblies by reduction in heat flow. Specifically, the moisture content of the existing roof deck and structural supports is of concern when insulation is added to the underside of the roof deck. Although installation of insulation to the underside of the deck may present challenges or concern regarding roof decks or roof coverings (for example, when converting to an unvented attic condition or to enclosed rafter spaces), creative design techniques may permit adding insulation below-deck while maintaining a ventilation space immediately below the roof deck. 5.1.3 Alterations to Attic or Interior Ambient Conditions— Any time the temperature or relative humidity, or both, immediately below a roof enclosure or within the attic space of a roof enclosure is altered, the impacts on the roof deck and the structural framing members should be assessed. It is common practice for owners or designers to upgrade existing buildings by adding modern HVAC systems while seeking to prevent excessive energy losses through the attic. A common project goal is to bring the roof and attic space up to current energy code with respect to insulation and air barriers. Additionally, the presence of mechanical equipment, sprinkler systems, or other specialized equipment within the attic space often results in the need to condition portions of, or the entire, attic space. This could have implications on the performance of the roof enclosure. 5.1.4 Addition of Vapor Retarders— Adding any vapor impermeable material to an originally vapor permeable roof enclosure has the potential to alter the hygrothermal performance of the overall roof enclosure. This may lead to an unintended accumulation of moisture which would not have occurred prior to the addition of any impermeable material, whether the material is intended to serve the function of a vapor retarder or not.