Stretch Code

Adopted in May 2009, the ‘Stretch’ energy code (formerly known as Appendix 115.AA), is an optional energy code for towns and cities in Massachusetts. Every municipality classified as a  Green Community is required to adopt the Stretch code. About half of the MA population lives in a Stretch code municipality.

The Stretch code amends the base energy code (currently 2009 IECC) to achieve approximately a 20% improvement in building energy performance. It features a performance code compliance path, as opposed to the more familiar prescriptive path of typical energy codes. The performance path requires a HERS rating to model the energy use of the building.

Please check  here to see if your town follows this code.

How it works:


New residential buildings 3-stories or less are required to meet an energy performance standard using the Home Energy Rating System ( HERS). 

The HERS index 

  • Rates each home on a scale where 0 is a zero-net-energy home, and 100 is a typical new home built in 2006. 
  • The HERS index has been in use for many years in programs such as: Energy Star homes, LEED homes, and by the Federal IRS to qualify homes for tax credits and energy efficient mortgages. 
  • HERS ratings are performed by a HERS Rater, an independent certified building energy professional, working with the home builder. HERS ratings are submitted to the local building code official in draft form at plan review and final form on building completion.

The Stretch Code does not apply to the following situations:

  • Storm windows added to existing windows
  • Window repairs to an existing sash and frame
  • Re-roofing or residing over uninsulated roofs or walls where the sheathing is not exposed.

New Home Requirements: 

  • 3,000 ft2 or larger: HERS index of 65 or less
  • less than 3,000 ft2: HERS index of 70 or less
  • Multi Unit Buildings

     The unit size determines the HERS score needed.

In addition:

  • Mandatory requirements of the base energy code (IECC 2009)
  • Builders and HERS raters must complete the Energy Star Homes Thermal checklist.

Existing Home Renovations & Addition Requirements

Home additions and renovations have two options to meet the stretch code:

Option 1) Performance path: whole house, HERS rating option

  • Existing homes 2,000 ft2 or larger: HERS index of 80 or less
  • Existing homes less than 2,000 ft2: HERS index of 85 or less
  • Home additions less than 3,000 ft2 : HERS index of 70 or less
  • Home additions 3,000 ft2or larger: HERS index of 65 or less

In addition:

  • Mandatory requirements of the base energy code (IECC 2009)
  • Builders and HERS raters must complete the relevant portions of the Energy Star Homes Thermal checklist.

Option 2) Prescriptive path: partial house option (HERS rater not required)

  • Any portions of a building modified by renovation must be brought up to code, or insulated to fill open wall/ceiling/floor cavities whichever is less.
  • Any new windows, doors or skylights must meet Energy Star 5.0 standards.
  • Any new ducted heating or cooling systems outside the insulated space must be tested and meet a maximum of 4% leakage to outside.
  • Builders must complete the relevant portions of the Energy Star Homes Thermal checklist.

Commercial Buildings

The stretch code applies to new commercial buildings and additions over 5,000 ft 2


  • New commercial buildings smaller than 5,000 ft2
  • Existing commercial building renovations,
  • Specialty buildings – supermarkets, laboratories, and warehouses – less than 40,000 ft2, due to their widely differing energy needs.

*These Stretch Code Exempt buildings remain subject to the base MA commercial energy code (IECC 2009 or ASHRAE 90.1-2007 with MA amendments).*

New large commercial buildings over 100,000 ft2 and Specialty buildings over 40,000 ft2)

These buildings are required to meet a Performance standard set at 20% below the base energy code. This is based on predicted energy use compared to the commonly used ASHRAE 90.1-2007 standard. This method is also used by buildings applying for LEED energy certification.

New medium-sized commercial buildings (between 5,000-100,000 ft2)

These buildings have two options. They can either use the large building Performance standard or use a Prescriptive path: a modified version of the base energy code (IECC Chapter 5).

The Prescriptive path adds incremental efficiency improvements to the base energy code primarily through:

  • Building envelope elements ( better walls, roofs, windows, insulation, etc.)
  • Commissioning tests to ensure that building energy systems operate as designed
  • More efficient lighting power densities and improved lighting controls
  • One of three options: high efficiency HVAC equipment, further lighting energy reductions, or on-site renewable energy