Secretary of the Interior Standards

Illustrated Guidelines for Rehabilitating Historic Buildings; BUILDING Exterior - Windows (1992).
Prepared by: Technical Preservation Division, National Park Service.

This document provides a description of the U.S. Secretary of the Interior’s Standards for Rehabilitation before introducing the Guidelines for Rehabilitation. The Guidelines are intended to be used together with the Standards for Rehabilitation to provide a model process for property owners, developers, and Federal agencies. The “Windows” section provides a brief history of windows followed by a “Recommended” section in which approaches, treatments, and techniques that are consistent with the Secretary of the Interior’s Standards for Rehabilitation are discussed. Approaches, treatments, and techniques that may adversely affect a buildings character are discussed in following section titled “Not Recommended.” Photographs accompany various treatments to provide a visual example for the reader. Read here

Preservation Brief #9 – The Repair of historic Wooden Windows (1981). Prepared by: Technical Preservation Division, National Park Service.

This technical brief explains the architectural significance of windows and provides guidance on preserving, rehabilitating, and restoring historic windows. This publication helps historic property owners recognize and resolve common issues prior to starting their window project. Additionally, this brief is particularly useful to property owners that may be seeking local, state, or federal tax credits because it recommends methods and approaches for rehabilitating historic windows that are consistent with their historic character. Read here

Preservation Brief #13 – The Repair and Thermal Upgrading of Historic Steel Windows (1981). Prepared by: Technical Preservation Division, National Park Service. Read here

General Information on Historic Windows

Historic Window Guide (n.d.). Prepared by:  the Conservation Team,  Tewkesbury Borough Council.

This guide provides an illustrated history of window development in the United Kingdom from the Middle  Ages to the present and a clear and concise explanation to the question, “Why are windows important?” Numerous photographs, diagrams, and illustrations are used to provide examples of styles, designs, and construction techniques of historic windows. This guide also provides a section on the history of glass and a glossary of window terms. Read here

Historic Windows (n.d.) By the Historic Preservation Education Foundation

This website is home to the on-line exhibit “Windows Through Time”.  The exhibit documents the history windows in the United States from 1630 through the 1950s by cataloging historic windows. Each entry contains a photograph of a historic window, its location, dimensions, a physical description and some historic background. The catalog’s examples are an interesting collection that show how various windows were used in different types and styles of buildings. Read here

Windows of Opportunity: Repair - Don’t Replace - Those Older Wood Windows (2013). By Rebecca Williams, National Trust for Historic Preservation.

This short article discusses the benefits of retaining historic windows and makes the case for repair over replacement. In addition, the author provides some easy, low-cost tips for increasing the energy efficiency of historic windows and provides additional resources for further reading. Read here

This booklet was created to identify issues common to original windows in vintage and historic homes in Portland, Oregon and to offer solutions for how these issues can be resolved without seriously impacting historic character. In many instances, the tips in this booklet may be applied to other parts of the Pacific Northwest where similar building materials are commonplace. Read here

Energy Efficiency

What Replacement Windows Can’t Replace: The Real Cost of Removing Historic Windows (2005). By Walter Sedovic and Jill H. Gotthelf. APT Bulletin: Association For Preservation Technology Vol. 36 No. 4.

This article discusses replacing historic windows in the context of preservation and sustainability. The authors use a scientific approach to evaluate various windows replacement options and historic window rehabilitation. They provide data regarding embodied energy values for various materials and provide a “Windows Replacement Worksheet” designed to help property owners estimate the savings (or lack thereof) of replacing existing windows with energy efficient upgrades. The issues of air infiltration, heat loss/gain, performance and material quality, aesthetics and authenticity, and ease of maintenance are also discussed. Read here

This article discusses the comparisons between replacement windows and historic double hung windows and includes testing completed by the Window Preservation Standards Collaborative showing different types of restoration and weatherstripping techniques and their relative effectiveness on the efficiency of historic wood windows.

Read here

Evaluating the Energy Performance of Window Retrofit and Replacement

Homeowners and design professionals seeking to upgrade the performance and efficiency of existing windows are faced with many choices—from simple, low cost, do-it-yourself solutions such as window films and weather stripping to replacing older windows with new ones that require investments costing tens of thousands of dollars. Often these decisions are made without a clear understanding of the range of options available, an evaluation of the ability of these options to provide energy and cost savings, or proper consideration for the historic character of the existing windows. This study builds on previous research and examines multiple window improvement options, comparing the relative energy, carbon, and cost savings of various choices across multiple climate regions. Results of this analysis demonstrate that a number of existing window retrofit strategies come very close to the energy performance of high-performance replacement windows at a fraction of the cost. Read here

The replacement window industry says that single-pane wood windows cannot be energy efficient and must be replaced. The local historic district design guidelines say that historic windows must be retained, seemingly without regard to energy efficiency. The homeowner is caught in the middle without the facts. The truth is that windows (old or new) are never highly energy efficient when compared with other materials. Will triple-glazed, Low-e, argon gas-filled replacement windows decrease heat loss to a level below that which is allowed by a historic window? Chances are that it will. The big question, though, is whether the decrease will result in a cost savings that makes replacing the windows cost effective. In general, the answer is no. This paper will elaborate on this point. Read here

Reports and Studies

Testing the Energy Performance of Wood Windows in Cold Climates: A Report to the State of Vermont Division for Historic Preservation (1996). Agency of Commerce and Community. Conducted By Brad James and Dr. David Hemenway, Department of Civil and Environmental Engineering, University of Vermont; Andrew Shapiro, Energy Engineer, Vermont Energy Investment Corporation; and, Steve Flanders, Research Civil Engineer, U.S. Army Cold Regions Research and Engineering Laboratory.

This study proposes to investigate “…the types of historic windows and viable methods for striking the balance between retaining a window’s historic character and energy efficiency.” In short, it was undertaken to test the assumption that historic wood windows can be retained and upgraded to approach the thermal efficiency of replacement sash or window inserts. This is a lengthy and scientific study presented in a scholarly format. Read here

A Comparative Study of the Cumulative Energy Use of Historical Versus Contemporary Windows (2010). By Frank Shirley, AIA. Fred Gamble, PhD, Jarod Galvin, RA, LEED AP.

This study provides a great side by side comparison of the life-cycle costs of historic windows and replacement windows. The study was conducted in a pre-1940 house in Boston, Massachusetts and provides the total present value of all costs associated with a window system over its entire life. The study offers reasonable cost information and a great bibliography. Read here

Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement (2016). Produced by the Preservation Green Lab.

Among the most recent reports on this topic, this report offers insight for homeowners weighing the financial and energy tradeoffs between repairing and replacing historic windows. The analysis builds on previous research by examining numerous window improvement projects and comparing them to replaced windows across multiple climate regions. This report offers property owners, contractors, and design professionals convincing evidence of the merits of retrofitting windows as opposed to outright replacement. Local municipalities struggling with the issues of repairing or replacing their windows would also benefit from reading this report. Read here

This study focused on empirical testing of the energy efficiency and economy of a range of options for upgrading the energy performance of historic windows. The study involved retrofitting windows in a test home in a historic district in Boulder, Colorado. It included testing in a window laboratory facility developed for the study. Read here