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Massachusetts proposes updates to the Stretch Energy Code

There’s still time left to comment on DOER’s proposed updates to the stretch code. The deadline for public comment is March 9th, 2022.

The Massachusetts Department of Energy Resources (DOER) has recommended updating the stretch code. The proposal is motivated by a statewide push for building electrification, specifically electric heat, which the DOER studies have shown is the most effective way to reduce greenhouse gas emissions from buildings.

What is the Stretch Code?

The stretch energy code is additional energy code requirements on top of the Massachusetts “base” Energy Code (Mass amendments to the 2018 IECC). Towns and Cities in Massachusetts can vote to voluntarily adopt the stretch code. Once the stretch code is adopted all updates to the stretch code are automatically enacted in those towns that have adopted the stretch code, which means if the proposed updates are adopted, they will go into effect in all stretch code towns (most of Massachusetts).

The Proposed Updates

A significant update to the stretch code is the creation of an opt-in “Net Zero” code, creating a third energy code option in Massachusetts. Like the stretch code, this code can be voluntarily adopted by towns and cities in Massachusetts. With this proposal, there would be three energy code options in Massachusetts:

  1. The Base Energy Code

  2. Stretch Code

  3. Opt-In “Net Zero”

It’s worth noting that Net-Zero typically refers to zero energy use on an annual basis, which means that the total energy used by the building equals the total energy produced on site by some form of renewable generation. That isn’t quite what it means in this context. The net zero code incentivizes buildings towards becoming all electric, or electrification ready, which means that these buildings will be net zero if and when the Massachusetts electric grid becomes net zero.


The residential portion of the proposed stretch code applies to one and two family homes, townhomes and small multifamily. There are three compliance pathways – two HERS (Home Energy Rating System), and one Passive House. The residential stretch code allows for slightly higher targets for buildings with electric heat, in an effort to push projects in that direction.

  • HERS 42 – for fossil fuel heated buildings (The base energy code is 52)

  • HERS 45 – for electric heated buildings (The base energy code is 55)

  • Passive house


For the commercial portions of the proposed stretch code, there will be five pathways for compliance, with the compliance pathway determined by the building use type.

  • Prescriptive Pathway (Small buildings <20,000 sf only)

  • Targeted Performance Pathway (Required for Offices & Schools, Option for Multi-family)

  • Relative Performance Pathway (High ventilation and other buildings)

  • Passive house (Option for all building types)

  • HERS (Option for Multi-family)

Energy Modeling is an ingredient in most of these compliance pathways. The Relative Performance Pathway is most similar to the current stretch code requirements for buildings over 100,000 SF – an energy model based on ASHRAE 90.1 Appendix G. There Targeted Performance Pathway is new and will also use energy modeling to show that heating load is below a prescribed limit (kBtu/sf/yr) based on the building type.

Additional Requirements will apply to certain stretch code pathways. One additional requirement worth noting is an infiltration requirement of 0.25 cfm/sf (of building shell area) at 75 Pa. That’s about half of the air leakage allowed by the 2018 IECC for commercial buildings, and about 2-3 times more leakage that what is allowed by Passive House. Airtight construction is a critical element to reducing energy use in buildings, which is why the Passive House standard incorporates extremely tight construction as a pillar to achieving ultra-low energy use in buildings.

Opt-In Code

For the proposed Opt-In “Net-Zero” code, all compliance pathways are driving projects towards all electric buildings, which is consistent with Massachusetts’s goal to reduce greenhouse gas emissions in building.

  • All electric buildings would comply with no additional requirements.

  • Passive House buildings would comply if they are all electric, or electrification ready.

  • Buildings using fossil fuels would require solar on the roof where feasible (The solar PV does not need to meet the full electrical load of the building), and wiring for future electrification.