2025 Stretch Energy Code update! A step backwards, in a good way

It’s rare building codes go backwards. And hopefully it stays rare. With the current POTUS trying to roll back a slew of efficiency and renewable energy initiatives… maybe we’ll be building to the 2006 IECC , dusting off coal hoppers, and manufacturing single pane windows before too long! Bad joke, especially in Massachusetts.

Some Context: How we got to this Stretch Code update

The MA Stretch Code saw a huge update for all projects permitted after July 1, 2024. The HERS threshold requirements for existing buildings particularly caused some mayhem in the MA renovation world. The DOER listened and after due process, adjusted the Stretch Code, with updates going into effect in mid February 2025. This blog post provides some insight and calls out the biggest impacts. We are in support of these code updates, for the most part, and are confident that Massachusetts continues to lead the way to building decarbonization and normalizing high performance building practices.

Power House Energy Consulting is a HERS Rating firm that works closely with designers , homeowners, and builders in designing and building to energy codes. We have a unique perspective on this space, and therefore are moved to provide some input with insights included below in bold.

This post is focused on the R, residential code, not the C, commercial code. The Specialized Stretch code (Appendix RC) does not have changes, outside of the inclusion of the embodied carbon HERS credit as summarized below.

Stretch Updates Effective February 14th 2025

Full draft here on the DOER website.

Red text in the excerpts below are the changes to the current 2021 IECC Stretch Code, that went into effect for all projects permitted after July 1, 2024.

As there is rarely a relaxing of energy code stringency, there is a bit of a question how municipal building commissioners will chose to enforce projects permitted under the current Stretch but complete under this update. We expect allowances to be made if homes meet new code, but do not neet the code under the permit date.  Of course this should be confirmed with building official in the relevant jurisdiction. 

Finally, we want to commend DOER and other MA stakeholders for these revisions and for keeping the Stretch Code strong. They perhaps went a bit too far in July ‘24. Yet until you test the edges, push comfort levels, you don’t know what can work in order to have the greatest impact. Unlike Federal unraveling of climate initiatives, Massachusetts State acknowledges the climate emergency we are in. The efforts to build on well laid foundation of advanced energy codes, to strive for decarbonization of new and existing builders, is a hugely important task. It is not too late.

R406.5 - Updated HERS Requirements

New HERS Rating requirements are in Red

The table says all, and should be front of mind for all builders, developers, architects, and building officials. Cut it out and put it on the fridge!  Any early design conversations must reference these energy performance targets to avoid challenges and costs later in the project. The biggest HERS index change is in the last column, representing the significant impact of this Stretch update. Major additions/renovations now need to achieve a HERS index HERS of 65/70, up from 52/55 . 

INSIGHT- This is a large HERS index increase (less efficient home), and we believe it is appropriate. Getting an old house to 52/55 HERS can be difficult. Over the last 18 months, folks doing major additions or renovations had to make significant efforts to improve the ‘old’ house as well, in order to comply. In some ways, this made sense; if you are putting significant resources into building new, the code wanted the old house to be brought closer to current energy performance standards. Yet in reality, it stifled the market a bit too much. By keeping the HERS requirement but raising it, the code maintains the quality assurance, verification, and baselining inherent in the HERS system, yet enables homeowners to have more flexibility in their project , not necessarily prioritizing reduced energy loads for the entire house.

ADUs Have Higher HERS Rating Requirements A home that is permitted as an ADU can be less efficient than a larger new home, requiring 52/55 vs 42/45.

INSIGHT: I don’t quite understand this one. The only challenges with ADUs that we see hitting 42/45 HERS have to do with hot water systems, specifically when the home design does not accommodate a heat pump water heater in a sufficient interior mechanical space. The State could possibly exclude mechanical rooms from ADU conditioned floor area zoning requirements. Or they could have pushed Mass Save to offer a substantial split heat pump rebate for ADUs or all projects. A $3k incentive would result in equal pricing for proven split HPWHeaters, which can be in tight spaces (unlike integrated heat pump water heaters). OR, they could provide an incentive for a manufacturer to come up with a flat heat pump water heater that can live in a crawl space. Raising the HERS target for popular infill accessory homes is a step backward.

Historic Buildings Are Omitted from the HERS Rating Requirement In footnote ‘C,’ buildings classified as ‘Historic’ seem to now be omitted from HERS rating requirements entirely. 

INSIGHT: I do not understand this. Historic buildings should be considered on a per-building basis, as there is a huge variety of energy performance opportunities. This could result in our most structurally vulnerable buildings being targeted for lower-cost development. Especially of concern is that change of use for historic buildings does not have a HERS requirement any longer. The quality assurance of the HERS Rating is especially important for old buildings that benefit from quality control of install measures to establish an air barrier and prevent condensation risk. The prescriptive compliance pathway leaves a lot of room for poor installations, especially because building officials now often look to HERS Raters to provide important insights relating to insulation and air barrier installation- if there is no Rater on the project, a less comprehensive enclosure assessment is likely.

There are better ways to create prescriptive carve outs for historic buildings. Such as for occasions when windows can’t be updated. The solution here could be a compliant HERS Report with a baseline code window (U.30) and then an approval for increased HERS index with maintaining single panes windows as necessary for Historic district compliance.

R401.2 - HERS Rating Exceptions for Additions <1,000 sq ft  

Additions under 1000 sq ft of conditioned floor area do not trigger a HERS Rating requirement for the entire home. All new components or systems must follow the prescriptive code requirements (insulation prescriptive or U-A compliance with RESCHECK, duct testing, ventilation, etc.). Note that ‘Grade 1’ insulation and air barrier continuity are required in Table 402.4.1

INSIGHT: This provides some clarity. However there is a potential conflict with section R503.1.5, which requires a HERS rating if the addition is over 100% of the existing building floor area.  Does a 950 sq ft addition to a 900 sq ft existing home require a HERS rating as R503 states? Or per R401, is there an exception to the HERS Rating, requiring the prescriptive code compliance only?

R502.1.1 - Large Additions That Maintain Current Thermal Boundary Do Not Trigger HERS Rating 

If you are finishing a basement or an attic, you don’t need to complete a full HERS rating of the home. Yet if you are turning a basement or attic into a permitted dwelling unit, those new ‘homes’ would need to meet the <42/45 HERS requirement, (except in a historic registered home, apparently) . This adds some clarity to a fringe scenario that causes some confusion when living space is added without change to the building thermal enclosure.  

R503.1.5 - Major Renovations > 1,000 sq ft Conditioned Floor Area OR Over 100% of Existing Conditioned Floor Area Require HERS 

A home is required to achieve <65/70 HERS (remember HERS Ratings always include analysis of the entire home, not part of a home) when a major renovation impacts 50%+ of the home AND ALSO is >1000 sq ft (of floor area, not shell area, assumed) OR is over 100% of the existing conditioned floor area.

INSIGHT: The simple addition of ‘and also’ serves to clear up some confusion about this HERS Rating trigger for existing homes. ‘Level 3 Alteration’ is basically a major renovation impacting 50%+ of the home—there is slightly more nuance, but typically if you see it, you’ll know it. With the raised HERS thresholds by 20%, we support this clarification and the alteration aspect of the Stretch Code. There was confusion in the market for the first year under this original Stretch update, but everyone should be prepared for this by now.

It is up to the building officials, architects, and builders to understand the implication before designing, permitting, and generally scoping out renovation projects. With early awareness and early engagement with a HERS Rater to prepare to meet the updated HERS index targets, the result will be a better home, perhaps with fewer bells and whistles, but certainly with greater comfort and energy efficiency. Fortunately substantial Mass Save incentives through the R&A (Renovation & Addition) Program helps offset added expenses needed to drop the HERS through better envelope and HVAC performance . Through this program $20-$30k is on the table for electrification projects with modest envelope improvements.

R406.5.2 - Embodied Carbon HERS Credit - NEW

There are 2 paths for this embodied carbon credit, that allows higher HERS ratings if low carbon materials are used

HERS offset is allowed with verification of low-embodied carbon construction materials. There are two approaches: 1. modeled for the entire building enclosure 2. prescriptive low-carbon concrete. So if you are using low-carbon insulation and/or concrete, you can have a 5+% less efficient home.  There is a lot of language added for this new addition , so reference the full code for more.

INSIGHT: This is an exciting development and indeed a critical step if we are going to de-carbonize our buildings. The ugly truth is that any new building project uses a lot of materials, many of which come from fossil fuels. Concrete and closed-cell spray foam are the largest carbon loads in most buildings. Simply by creating an incentive for lower-carbon concrete, the market could move toward reducing embodied building energy.

What’s Still Missing from the Stretch Code ?

If you read this far, I’ll let you know that my pet peeve is nice balanced ventilation systems that don’t serve the house well because distribution is not thought through in design or disregarded by the install contractor. The MA Stretch Code should require basic distribution requirements and ventilation system commissioning. For example , require that ERV and HRV are actually balanced, and that fresh air goes to bedrooms or within 10’ of bedrooms, and exhaust stale air leaves from wet rooms (bath, kitchen , or mudroom) or 10’ from these spaces. This would ensure our high performance homes work as designed to serve the occupants and improve building durability.