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


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