(a)(1) All Federal agencies shall design new Federal buildings that are low-rise residential buildings, for which design for construction began on or after January 3, 2007, but before August 10, 2012, to:

(i) Meet the IECC 2004 (incorporated by reference, see § 435.3), and

(ii) If life-cycle cost-effective, achieve energy consumption levels, calculated consistent with paragraph (b) of this section, that are at least 30 percent below the levels of the IECC Baseline Building 2004.

(2) All Federal agencies shall design new Federal buildings that are low-rise residential buildings, for which design for construction began on or after August 10, 2012, but before January 10, 2018 to:

(i) Meet the IECC 2009 (incorporated by reference, see § 435.3), and

(ii) If life-cycle cost-effective, achieve energy consumption levels, calculated consistent with paragraph (b) of this section, that are at least 30 percent below the levels of the IECC Baseline Building 2009.

(3) All Federal agencies shall design new Federal buildings that are low-rise residential buildings, for which design for construction began on or after January 10, 2018, but before April 5, 2023 to:

(i) Meet the IECC 2015, (incorporated by reference, see § 435.3), including the mandatory mechanical ventilation requirements in Section R403.6 of the IECC 2015; and

(ii) If life-cycle cost-effective, achieve energy consumption levels, calculated consistent with paragraph (b) of this section, that are at least 30 percent below the levels of the IECC Baseline Building 2015.

(4) All Federal agencies shall design new Federal buildings that are low-rise residential buildings, for which design for construction began on or after April 5, 2023 to:

(i) Meet the IECC 2021, (incorporated by reference, see § 435.3); and

(ii) If life-cycle cost-effective, achieve energy consumption levels, calculated consistent with paragraph (b) of this section, that are at least 30 percent below the levels of the IECC Baseline Building 2021.

(b)(1) For new Federal low-rise residential buildings whose design for construction began before January 10, 2018, energy consumption for the purposes of calculating the 30 percent savings shall include space heating, space cooling, and domestic water heating.

(2) For new Federal low-rise residential buildings whose design for construction began on or after before January 10, 2018, energy consumption for the purposes of calculating the 30 percent savings shall include space heating, space cooling, lighting, mechanical ventilation, and domestic water heating.

(c) If a 30 percent reduction is not life-cycle cost-effective, the design of the proposed building shall be modified so as to achieve an energy consumption level at or better than the maximum level of energy efficiency that is life-cycle cost-effective, but at a minimum complies with paragraph (a) of this section.