PERFORMANCE: Codes & Standards

International Green Construction Code and ASHRAE Standard 189

In order to provide adoptable and enforceable baselines for green construction, the International Code Council (IECC) and ASHRAE have established the International Green Construction Code (IgCC) and ASHRAE/USGBC/IES Standard 189.1. These can be adopted by jurisdictions in addition to conventional building codes.

International Green Construction Code (IgCC) Public Version 2.0
The IgCC covers land use, water conservation, energy conservation and other criteria.

  • The energy conservation section of the code requires that buildings over 25,000 square feet comply with performance-based goals that exceed the 2012 IECC.
  • The daylighting requirements include a minimum effective aperture and includes that 50% of the net floor area must be in daylit zones for 1-2 story buildings and 25% for buildings greater than 2 stories.
  • Both the IgCC and ASHRAE 189.1 require a certain amount of on-site renewable energy, which can include building integrated photovoltaics (BIPV).
  • The IgCC references ASHRAE Standard 189.1 as an optional compliance path.

Smaller buildings have more compliance options, including a prescriptive path. Regardless of the compliance option, fenestration must comply with the mandatory air leakage limits of the 2012 IECC. For fenestration and other building envelope systems, the prescriptive path requires that the 2012 IECC requirements are exceeded by at least 10%. The prescriptive path also requires permanent shading devices for fenestration facing east west and south.

ASHRAE/USGBC/IES Standard 189.1-2009
ASHRAE Standard 189.1 covers land use, water conservation, energy conservation and other criteria. The standard's energy efficiency section includes a performance option that requires detailed modeling and a prescriptive option with specific requirements such as U-factor and SHGC requirements and fenestration area limits. Regardless of the chosen compliance option, fenestration must not exceed mandatory air leakage limits.

The prescriptive option limits vertical fenestration area to less than 40% of the gross above-grade wall area. Office spaces and classrooms require a minimum effective aperture, which is the product of vertical fenestration area and visible transmittance. In climate zones with substantial cooling loads, the area of west- and east-oriented vertical fenestration is limited relative to north- and south-oriented fenestration, and permanent shading devices are required for fenestration facing east west and south.

The prescriptive option limits skylight area to 5% of the gross roof area. . In some larger spaces with high ceilings, the code requires a minimum skylight area for daylighting.

ASHRAE 189.1-2009 Prescriptive Fenestration Requirements
Climate Zone 1 2 3 4 5 6 7 8
Vertical Fenestration
Maximum U-factor
Framing materials other than metal with or without metal reinforcement or cladding
Non-metal frame 1.20 0.75 0.45 0.30 0.25 0.250.350.25
Metal framing with or without thermal break
Curtain wall/storefront 1.20 0.70 0.50 0.40 0.35 0.35 0.30 0.30
Entrance door 1.20 1.10 0.80 0.75 0.70 0.700.700.70
All other metal fram 1.20 0.75 0.55 0.45 0.45 0.450.450.35
Maximum SHGC
All vertical fenestration 0.25 0.25 0.25 0.35 0.35 0.400.450.45
Skylights with Glass
Maximum U-factor
with curb 0.71 0.71 0.69 0.690.670.670.670.58
with curb 0.57 0.57 0.45 0.45 0.45 0.450.450.45
Maximum SHGC
with or without curb 0.19 0.19 0.19 0.32 0.36 0.460.46Any

SHGC requirements for vertical fenestration are adjusted where shading by permanent projections exceeds the required minimum. Where skylights are integrated into daylighting design, SHGC requirements do not apply. For skylights with plastic and curb, different requirements apply than for skylights with glass or without curb.

Mandatory air leakage limits depend on the fenestration type. For windows, sliding doors, swinging doors and skylights, the maximum air leakage rate is 0.4 cfm/ft2.


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