In 2008, Massachusetts became one of the first states in the country to adopt the Green Communities Act. This act encourages energy conservation by having towns and cities pledge their support to be more energy-efficient and climate-conscious through grants and technical support. One of the requirements of this act is to adopt the “Stretch Energy Code,” which makes building codes more restrictive than the standard Massachusetts State Building Code. The stretch code is updated every three years when the International Energy Conservation Code (IECC) releases its updated edition.
At Town Meeting in 2019, Nantucket voted to become a “Green Community”, which went into effect on September 1, 2019. This effectively meant that Nantucket adopted a stricter set of building codes that dictate how we build, prioritizing energy efficiency. This applies to all new residential and commercial construction.
At Town Meeting in May 2024, there was an article that would have withdrawn us from the “Green Community” designation and would have dictated that we follow the base code, which is not as strict. Nantucket did not vote to withdraw from this designation, so for now, we are committed to following these guidelines, which became stricter on July 1, 2024.
The “Stretch Code” is based on something called a HERS Rating (Home Energy Rating System). This is a number value given to a home based on the insulating factors of all the products used to construct the home, and includes the energy efficiency of the mechanical systems. The R-value of the insulation used, the thermal envelope (the size of the framing used which allows for more insulation, for example, 2×4 vs. 2×6 construction), the types of windows used and their U-values, etc., all impact the energy efficiency of a building. It also includes the efficiency of the mechanical equipment used on the property, like the heating/cooling system, the type of hot water heater, type of lighting system, etc.
The HERS Rating is based on a scale from 1 – 100. The lower the number is, the “greener” and more energy-efficient the home. A score of 100 is the energy efficiency of a home built following the building code in 2006, so a building with a score of 52 is 48% more efficient than a home built in 2006. Until July 1, 2024, the HERS rating was 55 for new construction; after that date, the HERS rating for new construction became 42 (45 if the property has solar panels). If an addition is made to an existing structure that is less than 1,000 sq. ft., only the addition needs to meet these requirements. Once the addition is larger than 1,000 sq. ft. or larger than 100% of the existing structure, the code requires that the entire structure conform to the new HERS rating.
During the design process, the architect or designer shares all the materials to be used in construction with a third-party energy expert, the HERS Rater. The HERS Rater then inputs this information, including the size and type of windows, framing, insulation, etc., into a software program. What results is a number referred to as a Projected HERS Rating. In order to receive your building permit, this Projected HERS Rating must be submitted with the permit application. Throughout construction, your chosen HERS Rater will perform various inspections related to your final HERS Rating. At their final inspection, typically conducted as construction is wrapping up, they perform a blower door test, which measures building leakage; duct testing, which measures duct system leakage; and a mechanical air test, which measures indoor air quality.
These restrictions are challenging to meet in new construction across the board, but once we consider properties in downtown Nantucket and other historic properties, combined with the building restrictions Nantucket has on historic properties, it becomes much more complicated. For example, the HDC requires that windows in the historic district be single-pane since those are more historically accurate, but single-pane windows are obviously not energy efficient. In order to obtain building permits for structures like these, the structure needs a special designation as a historic structure to exempt it from these requirements.
The bottom line of these changes is that while the cost of building may increase, the cost to run the home in the future will be significantly less. Andersen Windows is one of the companies evolving their products to meet our building code needs. Last year they produced the first triple pane windows, which have the highest insulation factor (U-factor) of any window. The first run was for casement windows only. In the fall of 2024, Andersen came out with a line of double-hung, triple-pane windows, but unfortunately, these do not have muntin bars which the Historic District Commission prefers to see in all construction on Nantucket. It is our hope that as our needs evolve, window manufacturers will continue to expand the products they offer. Not surprisingly, the cost of these windows is 33% more per window, so it is a cost increase that will need to be factored into the construction budget.
In addition, closed-cell spray foam insulation is another material that can help achieve a more efficient thermal envelope. This is more expensive than other types of insulation, but combined with the fact that it offers a higher R-value per square inch and the fact that it is highly moisture resistant, it is the best material to use on Nantucket, where the humidity is high year-round. This type of insulation is more expensive, but the cost savings over the life of the house pay off in the long term. To adequately insulate a house, this means that the size of the framing used to build the house will have to increase in size. In November of 2024, a 2x4x10 is $7.73 per piece, a 2x6x10 is $13.39 per piece, and a 2x8x10 is $16.17 per piece.
As a side note, in the new code, one parking space per 1-2 family homes must be wired for an electric vehicle charger. Altogether, these changes do result in higher construction costs, but the cost savings can be seen down the road when the structure holds up to the elements well, and the cost for electricity, heating, and cooling costs are significantly less. Currently, the Massachusetts Department of Energy Resources has released a new draft of the stretch energy code and has asked for feedback from the community in which it has been requested that they loosen some of the codes to accommodate for special circumstances that were not considered when they released the new code in July 2024.
Stay tuned for the upcoming changes in 2025!
