Ashrae Building Envelope Trade Off Option

Ashrae building envelope trade off option

Ashrae building envelope trade off option


In many states and local jurisdictions, ASHRAE Standard 90.1 serves as the energy efficiency baseline for commercial buildings and residential buildings higher than three stories. The full name of this standard is ANSI/ASHRAE/IESNA Standard 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings. This standard is also referenced by voluntary programs such as LEED.

Ashrae building envelope trade off option

ASHRAE 90.1 sets minimum energy efficiency requirements for the design and construction of:

  • new buildings and their systems,
  • new portions of buildings and their systems,
  • and new systems and equipment in existing buildings.

Fenestration in new construction and additions as well as new fenestration in existing buildings is among the systems covered by ASHRAE 90.1. The choice among three compliance options determines the requirements for fenestration and other building systems:

  • Prescriptive building envelope option.

    The most straightforward compliance option.

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    Building components, such as fenestration, must meet prescriptive energy efficiency requirements. This compliance option limits the allowable window-to-wall area and skylight-to-roof area.

  • Building envelope trade-off option.

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    Provides flexibility regarding the performance of building envelope parts and allows any window-to-wall area, as long as the overall building envelope performance is at least equivalent to what it would be under the prescriptive option. The standard specifies a method for calculating the overall building envelope performance that accounts for how the visible transmittance of fenestration impacts daylighting potential.

  • Energy cost budget method.

    Ashrae building envelope trade off option

    Provides the greatest design flexibility, allowing any building design to comply as long as the overall simulated energy budget does not exceed the budget of a reference design that would meet the prescriptive requirements.

    This method requires detailed modeling that takes into account performance factors such as the impact of fenestration properties and orientation on daylighting potential and passive solar heating.

Fenestration Energy Ratings
Regardless of the chosen compliance option, the following fenestration energy properties are critical for compliance with the standard: U-factor, solar heat gain coefficient (SHGC), air leakage, and possibly visible transmittance.

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These properties must be provided as certified ratings determined by independent laboratories in accordance with National Fenestration Ratings Council (NFRC) standards. Air leakage ratings can also be based on the North American Fenestration Standard.

Georgia Commercial Building Envelope for ASHRAE 90.1-2013 & IECC-2015

A recent method for generating certified NFRC ratings for commercial fenestration is the Component Modeling Approach (CMA).

Versions of ASHRAE 90.1
The first ASHRAE Standard 90 was published in 1975.

Ashrae building envelope trade off option

Due to technology and pricing rapidly changing, the standard is continually maintained and updated. Beginning in 2001, the standard is published in its entirety every 3 years. The most current version is ASHRAE Standard 90.1-2010, although most state and local building codes still reference older versions of the standard (see for code status by state).

The links below provide overviews of the prescriptive fenestration requirements of different ASHRAE 90.1 versions:

ASHRAE Standard 90.1-2010 »

ASHRAE Standard 90.1-2007 »

ASHRAE Standard 90.1- 2004 »