Imagine completing a renovation, garage conversion, or addition, only to discover that the revised project scope triggers a HERS rating under the Massachusetts Stretch or Specialized Opt-In Energy Code.
Construction is finished. The walls are closed, insulation is covered, and the HVAC and water heating equipment are already installed. Nobody planned for energy modeling, blower door testing, or HERS verification.
Now what?
This situation can be more complicated than completing a HERS rating during construction, but it doesn't necessarily mean the project is in trouble. Depending on the building, available documentation, installed equipment, and opportunities for improvement, it may still be possible to achieve the required rating without major reconstruction.
I recently completed a HERS rating for a Massachusetts garage and accessory dwelling unit (ADU) project that illustrates exactly how this can happen.
How Can a Change in Project Scope Trigger a HERS Requirement?
One of the more common situations involves a project that changes direction after the original plans and permit application have been established.
A building might originally be planned as an office, garage, storage area, or another nonresidential space. During the project, the plans change and the space becomes a dwelling unit. A renovation may also expand into a larger addition or involve a more extensive alteration than originally anticipated.
Those changes can affect the applicable energy-code requirements.
In Massachusetts communities that have adopted the Stretch or Specialized Opt-In Code, certain additions, extensive alterations, Level 3 alterations, and changes of use can trigger HERS requirements.
The applicable requirements depend on the municipality, code edition, building classification, project scope, and the specific nature of the work. A change in use to a dwelling unit is particularly important because the energy code has specific provisions addressing spaces converted from another use or occupancy.
A project that began without a HERS requirement may therefore end up needing one after the scope changes.
If you're planning a project and aren't sure whether a HERS rating is required, see our guide: What Triggers a HERS Rating in Massachusetts?
What If the Building Is Already Finished?
The first step is to have a HERS rater review the completed project.
Rather than relying on the original plans alone, the rater needs to understand what was actually constructed. This includes reviewing the revised scope, available construction documents, installed equipment, insulation, windows, ventilation, and other components that affect the energy model.
The more information available, the better.
A homeowner or builder who has retained product specifications, purchase orders, equipment information, and construction photographs is in a much better position than someone trying to identify everything after the fact.
Gather the construction documentation
Before the HERS evaluation, try to collect:
Windows and exterior doors: Product orders, manufacturer information, U-factors, SHGC values, and specifications.
Insulation: Product names, installed R-values, installation details, and photographs taken before walls and ceilings were closed.
Heating and cooling: Manufacturer, model numbers, efficiency ratings, and AHRI certificates where applicable.
Domestic hot water: Water heater manufacturer, model number, efficiency rating, and installation location.
Appliances: Model numbers and applicable efficiency certifications.
Ventilation: ERV or other ventilation equipment specifications, duct layout, and airflow information.
Air sealing: Construction photographs and any available blower door test results.
Ductwork: Available duct leakage results and installation information.
These details can make a substantial difference in how accurately the completed building can be modeled.
Why Insulation Installation Matters
Having insulation specifications is important, but the product's advertised R-value doesn't necessarily tell the whole story.
Insulation installation quality matters when determining the performance credited in a HERS model.
When insulation is still accessible, the HERS rater can inspect the installation and assign the appropriate insulation grade based on what is actually observed. This includes looking for gaps, voids, compression, incomplete coverage, and other installation deficiencies.
If insulation is concealed, the rater may need to rely on available documentation, photographs, and applicable rating procedures to establish how the assemblies should be represented.
This is one reason construction photographs are so valuable. A photograph showing properly installed insulation before drywall was installed can help document conditions that are no longer visible.
The important distinction is that insulation specifications establish what product was intended, while inspection and supporting documentation help establish how it was actually installed.
A Real-World Example: A Garage with a Second-Floor ADU
I recently completed a HERS rating for a Massachusetts project where the original garage/office scope ultimately became a garage with an ADU on the second floor.
The project had already been completed before I became involved, and the HERS requirement had not been anticipated earlier in the process.
Fortunately, the homeowner had retained a considerable amount of documentation, including:
Window order and product specifications.
Insulation specifications.
Appliance information.
Domestic hot water equipment details.
Ductless mini-split heating and cooling equipment specifications.
That information allowed me to evaluate the completed ADU and build an accurate energy model using the equipment and materials actually installed.
After reviewing the project, I identified an opportunity to improve the rating by adding an energy recovery ventilator (ERV).
That was enough to bring the ADU into compliance.
The final HERS rating was 55, meeting the applicable all-electric ADU requirement.
In this case, the project did not require major reconstruction or opening finished walls to make the necessary improvement. Having the right documentation made it possible to identify a relatively straightforward path to compliance.
What if the project hadn't passed?
The ERV was sufficient for this particular project, but that won't always be the case.
If the initial model had not met the required HERS threshold, I would have evaluated several additional opportunities:
Upgrade the domestic hot water system. Replacing a conventional electric water heater with a qualifying heat pump water heater could provide a meaningful improvement, depending on the existing equipment and model.
Improve the blower door result. Additional air sealing may be possible, even after construction, depending on accessibility and the areas contributing to leakage.
Evaluate the heating and cooling equipment. A higher-efficiency heat pump system may improve the rating if the existing equipment is less efficient.
These are potential strategies, not guaranteed solutions. The best approach depends on the actual building, available improvements, equipment specifications, and how much improvement the model requires.
The important thing is to identify the opportunities before recommending unnecessary work.
Why It's Better to Involve a HERS Rater Before Construction Is Complete
A HERS rater involved during the design and construction process can help identify potential compliance issues before they become expensive problems.
Preliminary modeling establishes whether the proposed plans and specifications are likely to meet the required HERS threshold. Midpoint inspections provide an opportunity to evaluate insulation and air-sealing details while they are still accessible. Equipment selections and changes can be reviewed before installation.
When a rater becomes involved after construction, those opportunities are more limited.
The rater is working with what was built, what can be verified, and whatever improvements remain possible.
That doesn't mean a late-stage HERS rating cannot succeed. It simply means the process may require more investigation and fewer options may be available.
The Takeaway: Keep Your Documentation and Revisit the Code When Your Project Changes
If your renovation, addition, garage conversion, or other project changes scope, don't assume the original energy-code requirements still apply.
A change in use, occupancy, project size, or construction scope can affect whether a HERS rating is required in a Massachusetts Stretch or Specialized Opt-In community.
If you discover the requirement after construction, don't assume the project cannot pass. Start by gathering the available documentation and having a HERS rater evaluate the completed building.
As my recent garage/ADU project demonstrates, a project that wasn't originally planned around HERS compliance may still have a path forward. In that case, good documentation and one targeted improvement were enough to achieve the required rating.
The best time to involve a HERS rater is before construction begins. But if your project has already changed direction, the next best time is now.
