Stretch Code

The Massachusetts Stretch Energy Code was adopted by the Town of Nantucket on April 1, 2019 (Article 72 Bylaw Amendment) - Chapter 141 of the Town Code. All New Residential Dwellings and Large Commercial project applications will need to comply with the adopted code, effective as of September 1, 2019.

About the Stretch Energy Code

In 2009, Massachusetts became the first state to adopt an above-code appendix to the "base" building energy code-the "Stretch Code" (780 CMR Appendix 115.AA). The Stretch Code, which emphasizes energy performance, as opposed to prescriptive requirements, is designed to result in cost-effective construction that is more energy efficient than that built to the "base" energy code.

The Stretch Energy Code is an appendix to the Massachusetts Building Code, created by the Massachusetts Board of Building Regulations and Standards (BBRS). The purpose of the stretch energy code is to provide a more energy efficient code alternative for new buildings. It applies to all R-use buildings, of four stories or less above grade, all commercial building over 100,000 square feet, new supermarkets, laboratories and conditioned warehouses over 40,000 square feet.

The Stretch Energy Code is performance based as opposed to prescriptive, for R-use buildings the new homes/apartments must meet a HERS (Home Energy Rating System) index rating target, based on the total building envelope and mechanical efficiencies. The index rating is calculated by a certified HERS rater using specialized software program who is typically hired by the building contractor.


The HERS Rater is certified by the Residential Energy Services Network or RESNET and provides these energy rating and performance testing services.

1. The HERS Rater will produce a Projected Rating document from plans using specialized software that is submitted with the building permit application. The maximum HERS index score is currently 55.

2. The Rater makes a site visit after insulation to inspect what he or she will later have to confirm.

3. Near the projects end the Rater will conduct the required performance testing: a blower door test which measures the buildings leakage; duct testing which measures the duct system leakage and the mechanical air test to help insure good indoor air quality.

4. With all tests passed and completed the Rater logs the results with the RESNET Registry. The Confirmed Rating document is then submitted to the Building Official.

More Information

For more information, please visit Energy Provisions of the State Building Code (780 CMR).

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This page was last updated on August 6, 2019.