ASHRAE 90.1

ANSI/ASHRAE/IES Standard 90.1, Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings, is published by ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers) with the Illuminating Engineering Society. It sets minimum energy-efficiency requirements for the design of commercial and multifamily buildings and is one of the most influential energy standards in the world. The current edition is 90.1-2025. Its predecessor, 90.1-2022, incorporated more than 80 addenda to the 2019 edition and broadened the scope from buildings to "sites and buildings."

History

The standard grew out of the 1970s energy crisis. The first version was issued as ASHRAE 90-1975. It was later reissued as Standard 90.1 (the 1989 edition was 90.1-1989) and placed on continuous maintenance in 1999. Since 2001, new editions have appeared every three years (2001, 2004, 2007, 2010, 2013, 2016, 2019, 2022, 2025).

In the United States, the Department of Energy reviews each edition and issues a determination on whether it improves efficiency. A positive determination requires states to update their commercial energy codes to meet or exceed that edition.

Roof provisions

Section 5 (Building Envelope) sets requirements for roofs, including:

• Minimum insulation – maximum U-factors or minimum R-values for roof assemblies, varying by climate zone and roof type (insulation entirely above deck, metal building roofs, attic and other).
• Roof reflectance – the 2010 edition added minimum solar reflectance and thermal emittance requirements for low-slope roofs in warmer climate zones, with exceptions and trade-offs.
• Air leakage – continuous air barrier requirements that affect roof-to-wall transitions and penetrations.

The 2016 edition updated requirements for metal building roofs.

Relationship to other codes

Many US states adopt the International Energy Conservation Code (IECC), which allows ASHRAE 90.1 as an alternative compliance path for commercial buildings. California's Energy Code (Title 24) has a similar structure. Outside the US, 90.1 has been a model for national codes, including India's Energy Conservation Building Code.

Why it matters for roofs

Reroofing projects on commercial buildings frequently trigger energy code requirements to add insulation to current levels. Designers use 90.1 tables to determine how much insulation a new roof needs and whether a reflective surface is required.