How the NGBS Can Help You Navigate Green Renovations on Historical Properties

Remodeling
Published

The ICC 700-2020 National Green Building Standard® (NGBS) provides building professionals with a comprehensive, voluntary, above-code approach to design and construct residential and mixed-use properties and for land development. It also provides a flexible roadmap for green renovation projects — including the conversion of existing buildings to residential use, even if that building is subject to historical preservation regulations — in NGBS Chapter 11, ‘Certification for Existing Buildings.’

For instance, the process for converting an old factory building to new multifamily lofts includes:

  • Determining the number of units for the proposed design.
  • Calculating energy and water use for the proposed design with appropriate modeling tools.
  • Using the same number of units and configurations (studio, one‐bedrooms, two‐bedrooms, etc.), calculating energy and water use, using 1980 code requirements as a baseline.
  • Determining certification level using the difference in energy and water use pre‐ and post‐rehab.

Recognizing that there are challenges to renovating existing properties for residential use, especially historical ones, the NGBS provides flexibility to achieve project developers’ green building goals.

For example:
  • Buildings with historic designation restrictions are exempt from NGBS mandatory practices for unaltered portions.
  • If claiming exemption, building can use Performance Path for compliance or Prescriptive Path and select N/A for mandatory items that are not relevant.
  • Verifier must make detailed notes on verification report when exemptions are claimed.
  • Buildings with an addition of more than 75% of existing building’s above‐grade conditioned area should use new construction path unless there are historic preservation restrictions.
  • NGBS Green interpretation allows existing buildings to use NGBS exemptions for mandatory practices that apply to building portions that remain unaltered.

The Cargill Falls Mill project in Putnam, Conn., is a real-world example of this process. Located on the Quinebaug River, the historic mill has been transformed into more than nine acres of residential space — six interconnected buildings with 125 units. Steven Winter Associates served as the NGBS Verifier for the project.

Karla Butterfield, NGBS Green Master Verifier, of Steven Winter Associates noted: “As a historically registered landmark, the complex was under strict renovation requirements. The NGBS remodeling program was the only residential tool that allowed the project to quantify the energy and water savings while addressing the great efforts made by the project team to reduce material and resource consumption, improve indoor air quality, address sustainable site strategies, and promote health and wellbeing for residents.”

Learn more in this Home Innovation Research Labs case study.

To stay current on the high-performance residential building sector, with tips on water efficiency, energy efficiency, indoor air quality, and other building science strategies, follow NAHB’s Sustainability and Green Building efforts on Twitter.

Subscribe to NAHBNow

Log in or create account to subscribe to notifications of new posts.

Log in to subscribe

Latest from NAHBNow

Student Chapters | Workforce Development

Jul 25, 2025

NAHB's Student Chapters Helped Give Her Confidence to Pivot Careers

Zhetique Gunn's early exposure to building and problem-solving has led to national recognition and a city-level impact as an urban planner in Washington, D.C.

Jul 24, 2025

Federal Court Upholds New York State Gas Ban

The federal court for the Northern District of New York on July 23 upheld New York state’s “gas ban” legislation. New York’s legislation is the first statewide law that restricts natural gas use in new buildings, effectively banning gas stoves and other fossil fuel appliances in most new construction starting in 2026.

View all

Latest Economic News

Economics

Jul 25, 2025

Market Share of 5,000+ Square Foot New Homes Started Declines in 2024

In 2024, there were 24,000 homes that exceeded 5,000 square feet, equating to a 2.3% market share of all new homes started. Both the number and market share for 5,000+ square foot homes experienced declines from 2023, according to the annual data from the Census Bureau’s Survey of Construction (SOC).

Economics

Jul 24, 2025

New Home Sales Hold Steady at a Relatively Tepid Level

Challenging affordability conditions, elevated interest rates and economic uncertainty continue to act as headwinds on the housing sector as many potential buyers continue to stay on the sidelines.

Economics

Jul 23, 2025

Existing Home Sales Retreat to 9-Month Low

Existing home sales fell to 9-month low in June as home prices hit another monthly record high, according to the National Association of Realtors (NAR). Sluggish pace of sales suggest that higher mortgage rates and elevated home prices are continuing to sideline buyers, despite improved inventory conditions.