For Designers

Building Energy Code Requirements for Windows

Decisions to select a particular window are often strongly influenced by mandatory building energy codes or voluntary government and utility energy-efficiency programs. In states and localities that have adopted building energy codes, these codes typically set a minimum level of window thermal or home energy performance to which the builder, remodeling or replacement window contractor, or homeowner must adhere. As a result, the responsible decision-maker (builder, contractor or homeowner) should start the window selection process by first consulting building code requirements, since these requirements generally set the legal minimum level of energy efficiency that must be achieved. Voluntary programs, offered by both utilities and government agencies, provide homeowners and builders with complementary information about efficiency performance, direct or indirect financial incentives, or marketing support, all of which are intended to drive the market towards the selection of more efficient windows.

Building Energy Codes
Building codes differ from state to state and in some states even from local jurisdiction to jurisdiction. However, the majority of states today have adopted building codes that are mandatory statewide and that have an energy efficiency/conservation code subset intended to guarantee that a minimum level of cost-effective, energy-efficient technologies are part of the design package. These energy code requirements typically establish minimum threshold specifications or characteristics for buildings and their component products, whether they are windows, wall insulation, or other building components.

Building energy codes are adopted at a state or local level. With a few notable exceptions, most jurisdictions do not develop their own energy codes from scratch. Instead, they rely on adopting uniform model energy codes, such as the International Energy Conservation Code. Model energy codes are developed by national code writing entities and occasionally amended by jurisdictions to suit their particular needs.

Energy Code Requirements for Fenestration
Where building codes with mandatory energy requirements are in place, these typically set a minimum level of window thermal performance to which the builder, remodeling or replacement window contractor, or homeowner must adhere. Some older building energy codes only cover fenestration in new construction and only set U-factor requirements. Modern building energy codes, however, encompass fenestration for both new construction and replacement, and include SHGC requirements for warm climates.

Most modern building energy codes are modeled on the International Energy Conservation Code® (IECC), a model energy code that exists in different editions (1998, 2000, 2003, 2006), either of which has been adopted by different states and jurisdictions across the country. The latest version of the IECC (2006), which is adopted by an increasing number of states, provides simpler and more straightforward window requirements than its predecessors without sacrificing energy performance. Overall, the fenestration requirements in the 2006 IECC are fairly close to the qualification criteria for ENERGY STAR windows, doors, and skylights.

Example: Window requirements in the 2006 IECC
The table below shows the fenestration U-factor and SHGC maximums in the prescriptive compliance path of the 2006 IECC as an example of fenestration requirements in building energy codes. The requirements in the 2006 IECC are identical for windows in new construction and replacement windows, whereas other codes often have separate requirements for both purposes. View detailed information about IECC fenestration requirements.

 

Prescriptive window requirements in the 2006 IECC
Climate Zone Fenestration U-factor Skylight U-factor Glazed Fenestration SHGC
1 1.20 0.75 0.40
2 0.75 0.75 0.40
3 0.65 0.65 0.40
4 except Marine 0.40 0.60 no requirement
5-8 and Marine 4 0.35 0.60 no requirement