Significance and Use
Moisture degradation is frequently a significant factor that either limits the useful life of a building or necessitates costly repairs. Examples of moisture degradation include: (1) decay of wood-based materials, (2) spalling of masonry caused by freeze-thaw cycles, (3) damage to gypsum plasters by dissolution, (4) corrosion of metals, (5) damage due to expansion of materials or components (by swelling due to moisture pickup, or by expansion due to corrosion, hydration, or delayed ettringite formation), (6) spalling and degradation caused by salt migration, (7) failure of finishes, and (8) creep deformation and reduction in strength or stiffness.
Moisture accumulation within construction components or constructions may adversely affect serviceability of a building, without necessarily causing immediate and serious degradation of the construction components. Examples of such serviceability issues are: (1) indoor air quality, (2) electrical safety, (3) degradation of thermal performance of insulations, and (4) decline in physical appearance. Mold or mildew growth can influence indoor air quality and physical appearance. With some components, in particular interior surface finishes, mold or mildew growth may limit service life of the component. Moisture conditions that affect serviceability issues can frequently be expected, unless corrected, to eventually result in degradation of the building or its components. This guide does not attempt however to address serviceability issues that could be corrected by cleaning and change in building operation, and that would not require repair or replacement of components to return the building (or portions or components of the building) to serviceability.
Prevention of water-induced damage must be considered throughout the construction process including the various stages of the design process, construction, and building commissioning. It must also be considered in building operation and maintenance, and when the building is renovated, rehabilitated or undergoes a change in use.
This guide is intended to alert designers and builders, and also building owners and managers, to potential damages that may be induced by water, regardless of its source. This guide discusses moisture sources and moisture migration. Limit states (or specific moisture conditions that are likely to impact construction or component durability) and design methods are also cursorily discussed. Examples of practices that enhance durability are listed and discussed, as are examples of constructions or circumstances to avoid. The examples listed are not all-inclusive. Lastly, field check lists are given. The checklists are not intended for use as is, but as guides for development of checklists which may vary with specific building designs and climates.
1.1 This guide concerns building design, construction, commissioning, operation, and maintenance.
1.2 This guide addresses the need for systematic evaluation of factors that can result in moisture-induced damage to a building or its components. Although of great potential importance, serviceability issues which are often, but not necessarily, related to physical damage of the building or its components (for example, indoor air quality or electrical safety) are not directly addressed in this guide.
1.3 The emphasis of this guide is on low-rise buildings. Portions of this guide; in particular Sections 5, 6, and 7; may also be applicable to high-rise buildings.
1.4 This guide is not intended for direct use in codes and specifications. It does not attempt to prescribe acceptable limits of damage. Buildings intended for different uses may have different service life expectancies, and expected service lives of different components within a given building often differ. Furthermore, some building owners may be satisfied with substantially shorter service life expectancies of building components or of the entire building than other building owners. Lastly, the level of damage that renders a component unserviceable may vary with the type of component, the degree to which failure of the component is critical (for example, whether failure constitutes a life-safety hazard), and the judgement (that is, tolerance for damage) of the building owner. For the reasons stated in this paragraph, prescribing limits of damage would require listing many pages of exceptions and qualifiers and is beyond the scope of this guide.
1.5 This standard does not purport to address the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.