## ASHRAE 90.1 and 189.1 Glazing Provisions ### Overview ASHRAE Standard 90.1, "Energy Standard for Buildings Except Low-Rise Residential Buildings," and ASHRAE Standard 189.1, "Standard for the Design of [[Green Building Rating Systems Glazing Requirements|High-Performance Green Buildings]] Except Low-Rise Residential Buildings," are pivotal documents governing [[International Building Codes and Energy Standards|building energy efficiency]] in North America. Within the broader context of [[North American Glazing Regulations and Standards]], these standards establish comprehensive requirements for fenestration, including windows, glazed doors, and skylights, primarily focusing on their [[Thermal and Optical Performance Metrics|thermal and solar optical properties]]. Compliance is critical for new construction and major renovations, directly impacting a building's [[Operational Energy Savings and GHG Reduction Potential|operational energy consumption and greenhouse gas emissions]]. ### Technical Details #### ASHRAE 90.1 Fenestration Requirements ASHRAE 90.1 provides both prescriptive and performance-based pathways for [[Compliance Documentation and Certification Pathways|fenestration compliance]]. * **Prescriptive Path**: This path mandates specific maximum U-factors (thermal transmittance) and maximum Solar Heat Gain Coefficients (SHGC) for fenestration assemblies. These limits vary significantly based on the building's climate zone (as defined by ASHRAE Standard 169) and the fenestration type (e.g., vertical fenestration, skylights). For instance, in ASHRAE 90.1-2019, Climate Zone 5 (e.g., Chicago, IL), non-residential vertical fenestration might be limited to a U-factor of 0.38 Btu/h·ft²·°F (2.16 W/m²·K) and an SHGC of 0.39. These values are typically found in tables such as Table 5.5-4 for vertical fenestration and Table 5.5-5 for skylights. Meeting these values often necessitates the use of [[Advanced Glazing Technologies|high-performance glazing technologies]], including [[Low-Emissivity Coatings Types and Application]] and multi-pane [[Insulated Glass Units and Spacers]] with inert gas fills. The U-factor and SHGC values are determined according to [[U-value Calculation and Measurement Standards]] and [[Solar Heat Gain Coefficient and Solar Transmitta