Having made what it said are “targeted changes” based on the extensive public comment on its initial straw proposal in February, the Department of Energy Resources late last week filed draft language for the state building code changes that it hopes will encourage builders to shift away from fossil fuel heating in favor of electrification.

The Baker administration expects that its stretch energy code and specialized municipal opt-in code will save an estimated 500,000 tons of greenhouse gas emissions in 2030 with “no-to-minimal costs” to new construction, and $21 billion in construction and operating lifecycle costs. DOER said the draft regulations it filed with the secretary of state’s office Friday are generally “very consistent” with the straw proposal the department released in February.

Updating the existing stretch code and creating a new net-zero specialized stretch code for cities and towns to adopt is one of the more technical but meaningful steps Massachusetts is planning to take to be net-zero by the middle of the century. Residential and commercial building energy consumption was responsible for about 27 percent of the state’s greenhouse gas emissions in 2017.

The new net-zero code is required by last year’s climate roadmap law to be in place by the end of 2022 and was one of the more controversial aspects of the law, which Gov. Charlie Baker initially vetoed as developers warned that a net-zero stretch code would make the construction of new homes cost-prohibitive.

Key senators have been frustrated that the Baker administration’s stretch code does not authorize cities and towns to mandate that builders use all-electric heating, and the Senate’s wide-ranging climate bill calls for the creation of a “demonstration project” in which 10 municipalities could limit the use of fossil fuels in new construction. That bill is currently in conference committee negotiations with the House, which focused more on offshore wind policy in its bill.

Among the changes made to the February straw proposal, DOER said, was a strengthening of the specialized stretch code’s net-zero requirement for large residential homes, added clarity on the definition of net-zero building and a definition for zero-energy building as an optional code pathway, and clarity on effective dates. DOER said it received more than 1,200 written responses when it put the straw proposal out for public comment.

DOER said that it will provide an overview of the newest draft code language and respond to frequently asked questions during a recorded webinar planned for July 7. A public comment period on the latest draft will be open until 5 p.m. on Aug. 12. Comments can be emailed to stretchcode@mass.gov with the words “BUILDING CODE COMMENTS” in the subject line or mail to Ian Finlayson, Department of Energy Resources, 100 Cambridge St., Suite 1020, Boston, MA 02114.

The new code language will also be subject to three public hearings – July 22 at the Division of Fisheries and Wildlife field headquarters in Westborough, Aug. 2 at Thomas Crane Public Library in Quincy and Aug. 8 via a virtual meeting platform.

Since 2010, municipalities have had two options when it comes to picking a building code: they could adopt the state’s base energy code or, as 299 of the state’s 351 cities and towns have done, choose to use the stretch energy code first created in the Green Communities Act of 2008 as a requirement to become a Green Community. The code is meant specifically to “minimize, to the extent feasible, the lifecycle cost of the facility by utilizing energy efficiency, water conservation and other renewable or alternative energy technologies.”

Now, cities and towns will have a third option, one that DOER has referred to as a “climate-focused” specialized stretch code, which the 2021 climate roadmap law requires. DOER is also proposing updates to the base code that 52 municipalities rely on and to the more common stretch code. Unless a city or town decides to adopt the new specialized stretch code, it will continue to use whichever code it has adopted along with the latest updates.