For more than a decade now, the California Energy Commission (CEC) has utilized the National Fenestration Rating Council (NFRC) as its prescriptive standard for new fenestration products. You may have seen these standards referenced on newly installed windows through the use of labels that show certain performance values, such as the U-factor, Solar Heat Gain Coefficient (SHGC), and Visible Transmittance (VT). However, starting January 1st, 2023, the prescriptive reference standard for fenestration in new multifamily buildings will change from NFRC to NAFS.

NAFS is short for the North American Fenestration Standard/Specification for windows, doors, and skylights, a performance standard developed by the American Architectural Manufacturers Association (AAMA), now known as the Fenestration & Glazing Industry Alliance (FGIA) after merging with the Insulating Glass Manufacturers Alliance (IGMA) in 2020. The organization developed NAFS as a way to create a singular, simplified performance standard for customers across North America. NAFS has gone through several iterations over the last two decades, the latest being the 2017 edition, which is currently referenced in the 2018 International Building Code and 2018 International Residential Code. The 2022 California Energy Code has now adopted it prescriptively for new multifamily buildings, but what does this mean for new construction projects?

In Section 170.2 of the 2022 Energy Code (part of the new dedicated Multifamily section in the Energy Code), the prescriptive requirements for new construction reference the NAFS Performance Standard for an Architectural Window (AW), the highest standard based on various “Performance Classes” as defined through the NAFS, typically meant for residential glazing.

In terms of performance values for these types of windows, the Code still references the U-factor and VT, but the SHGC has been appropriately replaced with RSHGC (Relative Solar Heat Gain Coefficient), which is defined in the Energy Code as “… the ratio of solar heat gain through a fenestration product (corrected for external shading) to the incident solar radiation.” For specification and budgeting purposes, there won’t be much difference compared to NFRC, but the prescriptive values for the U-factor, RSHGC, and VT in residential applications are now defined through two factors: the number of stories, and the climate zone.

Below are the ranges of 2022 multifamily prescriptive fenestration standards for NAFS certified residential windows based on climate zone (CZ):

All New Multifamily Buildings (NAFS 2017 Performance Class AW)

U-factor: 0.38 for CZ 1 & 16; 0.40 for CZs 2-15

3 Stories and Below (NAFS 2017 Performance Class AW)

RSHGC: 0.24 for most CZs; not required for CZs 1, 3, 5, & 16

VT: Not Applicable

4 Stories and Above (NAFS 2017 Performance Class AW)

RSHGC: 0.35 for CZ 1; 0.24 for CZs 2-16

VT: 0.37 for all CZs

The burning question in every developer’s mind by this point is: will NAFS products be mandatory? And the answer is, “Nope!”

For clarity, NAFS is a new option for prescriptive compliance. By all current accounts, NFRC labeling will still be allowed when utilizing the performance method for new multifamily building envelopes, i.e. energy modeling. However, if utilizing this method, the prescriptive baseline (i.e. what the performance method is measured against) will fall under the “All Other Fenestration” category in Section 170.2, which has its own set of thermal performance values:

All New Multifamily Buildings (NFRC)

U-factor: 0.30 for CZs 1-6 & 9-16; 0.34 for CZs 6 & 7

3 Stories and Below (NFRC)

RSHGC: 0.23 for most CZs; not required for CZs 1, 3, 5, & 16

VT: Not Applicable

4 Stories and Above (NFRC)

RSHGC: 0.35 for CZ 1; 0.23 for CZs 2-16

VT: Not Applicable

Every code cycle introduces new and/or more stringent standards for developers to follow, and VCA Green’s team of Certified Energy Analysts (CEAs) are here to guide your new multifamily developments throughout California. For more information, contact Moe Fakih below.

Contributing Writer: Burke Boydell, CEA

Moe Fakih


714-363-4700 x 501