Standards and Design Guidance
Building Codes
Most locations have building energy codes that mandate minimum performance levels for windows, doors, and skylights. The builder, contractor, or homeowner must adhere to the code requirements, which typically cover windows for new construction as well as replacement windows. These requirements depend on the specific jurisdiction’s building energy code. Building energy codes are set at the state or municipal level. Most jurisdictions do not write their own building energy codes from scratch with a few exceptions. They rely on model energy codes developed by national code writing entities. National code writing entities modify model energy codes every few years, and jurisdictions may adopt any model code version, whether in whole or with modifications. For residential buildings, jurisdictions most often adopt a version of the International Energy Conservation Code (IECC); the latest edition was published in 2021. For commercial buildings, IECC and/or ASHRAE Standard 90.1 are typically used.
How do I find my energy code?
Energy efficiency requirements for windows vary not only by jurisdiction but also by climate. In the 2006 IECC and later, this variation is based on eight climate zones, with each county assigned to one climate zone. However, older versions of the IECC specify 19 different climate zones. Each model energy code establishes specific U-factor maximums for fenestration (with separate requirements for skylights) and SHGC maximums for all glazed fenestration.
It is important to understand the code requirements which apply to the location in question. The Building Codes Assistance Project (BCAP) keeps track of Energy Code Status throughout the US and provides details and links to state-specific codes. Using that information, you can review the generic IECC requirements below for guidance. Be aware that your specific state may have modified the code requirements pertaining to windows from the IECC baselines, which would make the requirements and Code Compliance Guides below invalid in your specific state.
State Code Compliance Guides
Code Compliance Guides providing information on compliance with state energy codes are published by the Responsible Energy Codes Alliance (RECA). These IECC Compliance Guides provide information regarding fenestration (windows, doors, and skylights), insulation, ducts, air sealing, systems, and lighting. First, determine which code is applicable, then find the correct guide.
Design Considerations
New windows influence energy use in both new and existing homes. The overall influence is impacted by five main factors. The specific climate is the biggest driver of overall performance and the biggest factor in making the proper window choice. Guides for hot, mixed, and cold climates are provided below. These guides show the impact of window selection, orientation, area, and shading conditions on energy use.
New Construction Guides
Hot Climate Design Guide for New Construction
Mixed Climate Design Guide for New Construction
Cold Climate Design Guide for New Construction
Existing Home Guides
Hot Climate Design Guide for Existing Homes
Mixed Climate Design Guide for Existing Homes
Cold Climate Design Guide for Existing Homes