treatment-guidelines-2017.pdf

THE SECRETARY

OF THE INTERIOR’S

STANDARDS FOR

THE TREATMENT

OF HISTORIC

PROPERTIES

WITH

GUIDELINES FOR

PRESERVING,

REHABILITATING,

RESTORING &

RECONSTRUCTING

HISTORIC

BUILDINGS

U.S. Department of the Interior National Park Service Technical Preservation Services

Under the National Historic Preservation Act (NHPA), the Secretary of the Interior is responsible for establishing professional standards and for providing guidance on the preservation of the nation’s historic properties. The Secretary of the Interior’s Standards for the Treatment of Historic Properties apply to all grants-in-aid projects assisted through the Historic Preservation Fund (authorized by the NHPA) and are intended to be applied to a wide variety of resource types, including buildings, sites, structures, objects, and districts. The Standards address four treatments: preservation, rehabilitation, restoration, and reconstruction. The treatment Standards, developed in 1992, were codified as 36 CFR Part 68 in the July 12, 1995, Federal Register (Vol. 60, No. 133). They replaced the 1978 and 1983 versions of 36 CFR Part 68, entitled The Secretary of the Interior’s Standards for Historic Preservation Projects. The revised Guidelines herein replace the Guidelines for Preserving, Rehabilitating, Restoring, and Reconstructing Historic Buildings, published in 1995 to accompany the treatment Standards.

The Secretary of the Interior’s Standards for the Treatment of Historic Properties are regulatory only for projects receiving Historic Preservation Fund grant assistance and other federally-assisted projects. Otherwise, these Guidelines are intended to provide general guidance for work on any historic building.

Another regulation, 36 CFR Part 67, focuses on “certified historic structures” as defined by the Internal Revenue Service Code of 1986.

The Standards for Rehabilitation cited in 36 CFR Part 67 should always be used when property owners are seeking certification for federal tax benefits.

THE SECRETARY OF THE INTERIOR’S STANDARDS

FOR THE TREATMENT OF HISTORIC PROPERTIES

WITH

GUIDELINES FOR PRESERVING, REHABILITATING,

RESTORING & RECONSTRUCTING HISTORIC BUILDINGS

Revised by Anne E. Grimmer from The Secretary of the Interior’s Standards for the Treatment of Historic Properties with

Guidelines for Preserving, Rehabilitating, Restoring & Reconstructing Historic Buildings

Kay D. Weeks and Anne E. Grimmer (1995)

U.S. Department of the Interior National Park Service Technical Preservation Services Washington, D.C.

II

CONTENTS

IV PHOTO CREDITS

VI ACKNOWLEDGEMENTS

VII PREFACE

2 INTRODUCTION

Using the Standards and Guidelines for a Preservation, Rehabilitation, Restoration, or Reconstruction Project

Choosing an Appropriate Treatment for the Historic Building

4 HISTORICAL OVERVIEW

Building Materials Masonry • Wood • Metals

Building Features and Systems Roofs • Windows • Entrances and Porches • Storefronts

• Curtain Walls • Structural Systems • Mechanical Systems

Interior Spaces, Features, and Finishes

Building Site

Setting (District/Neighborhood)

Code-Required Work:

Accessibility • Life Safety

Resilience to Natural Hazards

Sustainability

New Exterior Additions to Historic Buildings and Related New Construction

27 STANDARDS FOR PRESERVATION

& GUIDELINES FOR PRESERVING

HISTORIC BUILDINGS

29 INTRODUCTION

BUILDING MATERIALS

Masonry

Wood

Metals

BUILDING FEATURES AND SYSTEMS

Roofs

Windows

Entrances and Porches

Storefronts

Curtain Walls

Structural Systems

Mechanical Systems

60 INTERIOR SPACES, FEATURES,

AND FINISHES

63 BUILDING SITE

66 SETTING (DISTRICT/NEIGHBORHOOD)

69 CODE-REQUIRED WORK

69 Accessibility

71 Life Safety

72 RESILIENCE TO NATURAL HAZARDS

74 SUSTAINABILITY

75 STANDARDS FOR REHABILITATION

& GUIDELINES FOR REHABILITATING

HISTORIC BUILDINGS

77 INTRODUCTION

80 BUILDING MATERIALS

80 Masonry

88 Wood

93 Metals

98 BUILDING FEATURES AND SYSTEMS

98 Roofs

102 Windows

110 Entrances and Porches

113 Storefronts

117 Curtain Walls

121 Structural Systems

125 Mechanical Systems

128 INTERIOR SPACES, FEATURES, AND FINISHES

137 BUILDING SITE

143 SETTING (DISTRICT/NEIGHBORHOOD)

147 CODE-REQUIRED WORK

147 Accessibility

150 Life Safety

153 RESILIENCE TO NATURAL HAZARDS

155 SUSTAINABILITY

156 NEW EXTERIOR ADDITIONS TO HISTORIC

BUILDINGS AND RELATED NEW

CONSTRUCTION

163 STANDARDS FOR RESTORATION

& GUIDELINES FOR RESTORING

HISTORIC BUILDINGS

165 INTRODUCTION

III

IV

Contents Restoration (cont.)

168 MATERIALS

168 Masonry

176 Wood

180 Metals

184 BUILDING FEATURES AND SYSTEMS

184 Roofs

187 Windows

190 Entrances and Porches

193 Storefronts

196 Curtain Walls

199 Structural Systems

202 Mechanical Systems

204 INTERIOR SPACES, FEATURES, AND FINISHES

209 BUILDING SITE

214 SETTING (DISTRICT/NEIGHBORHOOD)

218 CODE-REQUIRED WORK

218 Accessibility

220 Life Safety

222 RESILIENCE TO NATURAL HAZARDS

224 SUSTAINABILITY

225 STANDARDS FOR RECONSTRUCTION &

GUIDELINES FOR RECONSTRUCTING

HISTORIC BUILDINGS

227 INTRODUCTION

230 OVERVIEW

232 BUILDING EXTERIOR

234 BUILDING INTERIOR

236 BUILDING SITE

238 BUILDING SETTING

(DISTRICT/NEIGHBORHOOD)

PHOTO CREDITS

Front Cover: Spooner Hall, University of Kansas, Lawrence, KS, Henry van Brunt, 1894.

HISTORICAL OVERVIEW

Masonry. Detail, decorative sandstone door surround.

Wood. Detail, Pope-Leighey House, Alexandria, VA, Frank Lloyd Wright, 1940. Photo: Courtesy National Trust for Historic Preservation, Paul

Burk, photographer.

Metals. Detail, Dunbar Molasses Factory, New Orleans, LA, c. 1920.

Glass. Detail, St. John’s Abbey, Collegeville, MN, Marcel Breuer, 1958-61.

Paint and Other Coatings. Interior detail, Mabel Tainter Memorial Theater, Menomonie, WI, Harvey Ellis, 1889. Photo: Miller Dunwiddie Architecture.

Composite Materials. Composite siding, Private Residence, Washington, DC, William Lescaze, 1940.

Simulative Materials. Detail, wood used to simulate cut stone.

Roofs. Asphalt roof shingles on a 1920s-era house.

Windows. Paired wood windows with stained glass lunette on a

Romanesque revival-style rowhouse.

Entrances and Porches. Decorative stone entrance with etched-glass revolving door on early-20th century office building.

Storefronts. Ellicott City, MD.

Curtain Walls. Simms Building, Albuquerque, NM, Flatow & Moore, 1954. Photo: Harvey M. Kaplan.

Structural Systems. Boiler Maker Shops, Navy Yard Annex, Washington, DC, 1919.

Mechanical Systems. Historic Radiator.

Spaces, Features, and Finishes. Interior, Saenger Theater, New

Orleans, LA, Emile Weil, 1927. Photo: Courtesy Saenger Theater.

Site. Vineyard, Charles Krug Winery, St. Helena, CA. Photo: Rocco Ceselin. Inset: Redwood Cellar, 1872, Charles Krug Winery. Photo:

Rien van Rijthoven.

Setting. Late-19th-century residential historic district.

Accessibility. Gradual slope added to sidewalk and paving for accessibility. Schmidt Brewery, St. Paul, MN, late 19th–early 20th century.

Life Safety. Code-required, supplemental stair railing.

Resilience to Natural Hazards. Farnsworth House, Plano, IL, Mies van der Rohe, 1951. Photo: Courtesy Farnsworth, A Site of the National Trust for Historic Preservation.

Sustainability. Traditional sustainable features include deep porches and window shutters in southern architecture.

New Additions and Related New Construction. Private Residence, Washington, DC, Cunningham/Quill Architects. Photo: © Maxwell MacKenzie.

CHAPTER HEADS

Preservation. Old Santa Fe Trail Building (National Park Service Intermountain Regional Office), Santa Fe, NM. This adobe building was designed by John Gaw Meem in the Spanish-Pueblo Revival style, and constructed for the National Park Service through the auspices of the Civilian Conservation Corps (CCC) and the Works Project Administration (WPA) in 1939. Photo: MRWM Landscape Architects.

Rehabilitation. The Arcade, Providence, RI, 1828. Photo: Northeast Collaborative Architects, Ben Jacobson, photographer.

Restoration. Montpelier, Montpelier Station, VA. National Trust for Historic Preservation, Administered by The Montpelier Foundation.

Photo: Courtesy The Montpelier Foundation.

Reconstruction. The Cathedral of Saint Michael the Archangel, Sitka, AK, built early 1840s, reconstructed 1961. Photo: Barek at Wikimedia Commons.

Photographs not individually credited are from National Park Service files.

V

VI

ACKNOWLEDGEMENTS

This edition of The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Buildings has been produced in part to ensure that the National Park Service continues to fulfill its responsibility to promote the preservation of the historic buildings that are part of the nation’s cultural heritage. This has been a collaborative effort undertaken by the office of Technical Preservation Services (TPS) in the National Park Service, with the assistance of other National Park Service programs, State Historic Preservation Offices (SHPO), the Advisory Council on Historic Preservation, Federal Agency Historic Preservation Officers, the National Trust for Historic Preservation, and others. The comments and suggestions provided by these agencies and organizations, together with important contributions from the TPS professional staff, have been invaluable in the development of this revised and updated guidance on preserving, rehabilitating, restoring, and reconstructing historic buildings that accompany The Secretary of the Interior’s Standards for the Treatment of Historic Properties.

PREFACE

The year 2016 was significant as the Centennial of the National Park Service, which was established as a new bureau within the Department of the Interior by the Organic Act on August 25, 1916.

As directed in this legislation, the National Park Service has served for one hundred years as steward of the “Federal areas known as national parks, monuments and reservations…to conserve the scen ery and the natural and historic objects and the wild life therein and to…leave them unimpaired for the enjoyment of future generations.”

The year 2016 also marked the 50th anniversary of the passage of the National Historic Preservation Act on October 15, 1966. The Act increased the scope and responsibilities of the National Park Service with regard to the preservation of cultural resources. The National Historic Preservation Act charges the National Park Service (through authority delegated by the Secretary of the Interior) to establish and administer a national historic preservation program and to develop and promulgate standards and guidelines for the treatment of historic properties.

The Secretary of the Interior’s Standards for Historic Preservation Projects were first issued in 1978. In 1979 they were published with Guidelines for Applying the Standards and reprinted in 1985. The Standards were revised in 1992, when they were retitled The Secre tary of the Interior’s Standards for the Treatment of Historic Properties.

The Standards were codified in the Federal Register in 1995, the same year that they were published with guidelines as The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Buildings. These Standards and Guidelines provide a critical part of the framework of the national preservation program. They are widely used at the federal, state, and local levels to guide work on historic buildings, and they also have been adopted by Certified Local Governments and historic preservation commissions across the nation.

In 2010 the National Park Service issued A Call to Action: Preparing for a Second Century of Stewardship and Engagement, a plan to chart a path for its next 100 years. This plan identified a number of actions with the goal to “preserve America’s special places in the next century,” which included updating National Park Service policies and guidance. The project to update The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Build ings was undertaken as part of this broader effort.

Since these Guidelines were first published in 1995, a greater number of buildings and building types, telling a broader range of stories that are part of the nation’s heritage, have been recognized as “historic”

VII

and eligible for listing in the National Register of Historic Places.

These guidelines have been updated and expanded to address the treatment of these buildings constructed with newer materials and systems from the mid- and late-20th century.

The updated Guidelines have the same organization as the prior version, beginning with an introduction and a historical overview, followed by chapters that focus on each of the four treatments:

preservation, rehabilitation, restoration, and reconstruction. The historical overview has been expanded; not only has the informa tion on historic materials, systems, features, and special issues that comprised the previous edition been more fully developed, but new entries have been added on glass, paint and other coatings, compos ite materials, imitative materials, and curtain walls.

In each of the four chapters, the “Recommended” and “Not Rec ommended” treatments have been updated and revised through out to ensure that they continue to promote the best practices in preservation. The section on exterior additions to historic build ings in the Rehabilitation Guidelines has been broadened also to address related new construction on a building site. A section on code-required work is now included in all of the chapters. “Energy Efficiency” has been eliminated, since it is more fully covered by the guidance provided on sustainability in The Secretary of the Interior’s Standards for Rehabilitation and Illustrated Guidelines on Sustainability for Rehabilitating Historic Buildings (published in 2011), which has general applicability to all the treatments and is incorporated here by reference. Sections on “Resilience to Natural Hazards” have been added, but these topics will be more fully addressed in separate documents and web features. Finally, the updated Guidelines feature all new, and many more, illustrations in color.

Herewith Technical Preservation Services issues the National Park Service Centennial edition of The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Buildings, updated and revised in recognition of the 50th anniversary of the National Historic Preservation Act, to ensure that the preservation guidance for historic buildings provided by the National Park Service contin ues to be meaningful and relevant in the 21st century.

Technical Preservation Services

VIII

Technical Preservation Services

The office of Technical Preservation Services (TPS) in the Cultural Resources directorate of the National Park Service is responsible for developing and promulgating preservation standards and guidance specifically as it relates to historic buildings. TPS has produced an extensive amount of technical, educational, and policy guidance on the maintenance and preservation of historic buildings. TPS developed the original and current versions of The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Buildings. The many technical publications and web features on preserving historic buildings prepared by TPS are well known, especially the Preservation Briefs and the Preservation Tech Notes series. It is not feasible to include a complete list here of all the materials available from TPS because of the sheer volume of information. Materials developed by TPS are available in printed form and/or online from the TPS website at https://www.nps.gov/ tps (or search for Technical Preservation Services at https://www.

nps.gov). TPS also administers the Federal Historic Preservation Tax Incentives Program, which encourages private sector investment in the rehabilitation and reuse of historic buildings.

IX

https://www.nps.gov/index.htm https://www.nps.gov/tps/ https://www.nps.gov/tps/ https://www.nps.gov/index.htm

INTRODUCTION

Using the Standards and Guidelines for Preservation, Rehabilitation, Restoration, and Reconstruction Projects The Secretary of the Interior’s Standards for the Treatment of His toric Properties address four treatments: preservation, rehabilitation, restoration, and reconstruction. As stated in the regulations (36 CFR Part 68) promulgating the Standards, “one set of standards …will apply to a property undergoing treatment, depending upon the prop erty’s significance, existing physical condition, the extent of docu mentation available, and interpretive goals, when applicable. The Standards will be applied taking into consideration the economic and technical feasibility of each project.” These Standards apply not only to historic buildings but also to a wide variety of historic resource types eligible to be listed in the National Register of Historic Places.

This includes buildings, sites, structures, objects, and districts.

Guidelines, however, are developed to help apply the Standards to a specific type of historic resource. Thus, in addition to these Guide lines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Buildings, there are also guidelines for cultural landscapes, historic lighthouses, historic vessels, historic furnished interiors, and historic covered bridges.

The purpose of The Secretary of the Interior’s Standards for the Treat ment of Historic Properties and Guidelines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Buildings is to provide guidance to historic building owners and building managers, preservation consultants, architects, contractors, and project reviewers prior to beginning work. It is always recommended that preservation profes sionals be consulted early in any project.

The Guidelines are intended as an aid to assist in applying the Stan dards to all types of historic buildings. They are not meant to give case-specific advice or address exceptions or unusual conditions.

They address both exterior and interior work on historic build ings. Those approaches to work treatments and techniques that are consistent with The Secretary of the Interior’s Standards for the Treatment of Historic Properties are listed in the “Recommended” column on the left; those which are inconsistent with the Standards are listed in the “Not Recommended” column on the right.

There are four sections, each focusing on one of the four treatment Standards: Preservation, Rehabilitation, Restoration, and Recon struction. Each section includes one set of Standards with accom panying Guidelines that are to be used throughout the course of a project.

Preservation is defined as the act or process of applying measures neces sary to sustain the existing form, integrity, and materials of an historic property. Work, including preliminary measures to protect and stabilize the property, generally focuses upon the ongoing maintenance and repair of historic materials and features rather than extensive replacement and new construction. The limited and sensitive upgrading of mechanical, elec trical, and plumbing systems and other code-required work to make prop erties functional is appropriate within a preservation project. However, new exterior additions are not within the scope of this treatment. The Standards for Preservation require retention of the greatest amount of historic fabric along with the building’s historic form.

Rehabilitation is defined as the act or process of making possible a com patible use for a property through repair, alterations, and additions while preserving those portions or features which convey its historical, cultural, or architectural values. The Rehabilitation Standards acknowledge the need to alter or add to a historic building to meet continuing or new uses while retaining the building’s historic character.

Restoration is defined as the act or process of accurately depicting the form, features, and character of a property as it appeared at a particular period of time by means of the removal of features from other periods in its history and reconstruction of missing features from the restoration period.

The limited and sensitive upgrading of mechanical, electrical, and plumb ing systems and other code-required work to make properties functional is appropriate within a restoration project. The Restoration Standards allow for the depiction of a building at a particular time in its history by preserving materials, features, finishes, and spaces from its period of significance and removing those from other periods.

Reconstruction is defined as the act or process of depicting, by means of new construction, the form, features, and detailing of a non-surviving site, landscape, building, structure, or object for the purpose of replicating its appearance at a specific period of time and in its historic location. The Reconstruction Standards establish a limited framework for recreat ing a vanished or non-surviving building with new materials, primar ily for interpretive purposes.

The Guidelines are introduced with a brief overview of the pri mary materials used in historic buildings; the exterior and interior architectural features and systems; the building’s site and setting;

code-compliance requirements regarding accessibility and life-safety resilience to natural hazards; sustainability; and new additions and related new construction. This overview establishes the format of the Guidelines that follow.

Choosing an Appropriate Treatment for the Historic Building The Guidelines are intended to promote responsible preservation practices that help protect the nation’s irreplaceable cultural resources. For example, they cannot, in and of themselves, be used to make essential decisions about which features of the historic building should be saved and which can be changed. But, once a treatment is selected, the Standards and Guidelines provide a consistent philosophical approach to the work.

Choosing the most appropriate treatment for a building requires careful decision making about a building’s historical significance, as well as taking into account a number of other considerations:

Level of Significance. National Historic Landmarks, designated for their “exceptional significance in American history,” and other properties important for their interpretive value may be candidates for Preservation or Restoration. Rehabilitation, however, is the most commonly used treatment for the majority of historic buildings Reconstruction has the most limited application because so few resources that are no longer extant can be documented to the degree necessary to accurately recreate the property in a manner that con veys its appearance at a particular point in history.

Physical condition. Preservation may be appropriate if distinctive materials, features, and spaces are essentially intact and convey the building’s historical significance. If the building requires more extensive repair and replacement, or if alterations or a new addition are necessary for a new use, then Rehabilitation is probably the most appropriate treatment.

Proposed use. Many historic buildings can be adapted for a new use or updated for a continuing use without seriously impacting their historic character. However, it may be very difficult or impossible to convert some special-use properties for new uses without major alterations, resulting in loss of historic character and even integrity.

Code and other regulations. Regardless of the treatment, regula tory requirements must be addressed. But without a sensitive design approach such work may damage a building’s historic materials and negatively impact its character. Therefore, because the ultimate use of the building determines what requirements will have to be met, some potential uses of a historic building may not be appropriate if the necessary modifications would not preserve the building’s historic character. This includes adaptations to address natural hazards as well as sustainability.

HISTORICAL OVERVIEW

Masonry Stone is one of the more lasting masonry building materials and has been used throughout the history of American building construc tion. Stones most commonly used in historic buildings in the U.S.

are quarried stone, including sandstone, limestone, marble, granite, slate, basalt, and coral stone, and gathered stone, such as fieldstone, river rock, and boulders. Types of stone differ considerably in hardness, durability, and other qualities. Building stones were usually laid with mortar, but sometimes they were laid without mortar using a dry-stack method of construction. Brick varies in size and permanence. Before 1870, brick clays were pressed into molds and were often unevenly fired. The quality of historic brick depended on the type of clay available and the brick-making technique; by the 1870s, with the perfection of an extrusion process, bricks became more uniform and durable. Architec tural terra cotta is also a kiln-fired clay prod uct popular from the late 19th century until the 1930s. Its use became more widespread with the development of steel-frame, high-rise office buildings in the early 20th century.

Glazed ceramic architectural siding was also used as cladding in high-rise buildings some what later. Adobe, which consists of sun-dried earthen bricks, was one of the earliest build ing materials used in the U.S., primarily in the Southwest where it is still popular.

Mortar is used to bond together masonry units. Historic mortar was generally quite soft, consisting primarily of lime and sand with other additives.

Portland cement, which creates a more rigid mortar, was first manu factured in the U.S. in the early 1870s, but it was not in common use throughout the country until the early 20th century. Thus, mortar used in buildings from around 1873 until the 1930s ranged from a tra ditional lime-cement mix to a variety of sand and Portland cement combinations. After this time, most mortar mixes were based on Portland cement. Like historic mortar, early stucco was also heav ily lime based, increasing in hardness with the addition of Portland cement in the late 19th century.

Concrete has a long history. It is composed of sand, crushed stone, or gravel bound together with lime and, sometimes, natural hydraulic cements. As a construction material concrete is used in a variety of forms, including blocks or units, poured or cast-in-place, and precast panels. Cast stone and other manufactured products began to be used around the 1860s as substitutes for natural stone. There are also cementitious materials specific to certain regions, such as tabby, which includes crushed shells and is found primarily in coastal areas in the southeastern part of the country. In the 20th century, rein forced concrete was developed and has since become one of the most commonly used materials in modern building construction.

While masonry is one of the most durable historic building mate rials, it is also very susceptible to damage by exposure, improper maintenance or repairs, abrasive cleaning, or the application of non-permeable coatings.

Wood Wood is one of the most essential materials used in American build ings of every period and style. Its many and varied attributes make it suitable for multiple uses, including structural members, siding, roofing, interior finishes, and decorative features. Many of the first structures in the earliest settlements were built with logs, which were readily available, did not require much finishing, and could be quickly erected with basic tools.

Water-powered sawmills cut logs into timbers and boards, but detailed ornamental features were generally crafted on site using hand tools until after the Civil War. Mechanized production increased the efficiency of cutting logs into timbers, boards, and more intricate components, and the structural and decorative poten tial of wood’s use in building construction expanded. With more efficient production came lower costs, but also the standardization of ready-made moldings and assemblies for windows, doors, and decorative features. Initially, wood was primarily sourced locally, but improved transportation systems made a greater variety of wood species more accessible all over the country. With broader availabil ity, a particular wood could be selected for its suitability in a specific application; however, local species were used most often.

The extensive use of wood in buildings can be attributed to its many properties that include strength in both tension and compression;

ease with which it can be cut and shaped; capability to be connected using a variety of fasteners and adhesives; ability to be painted or varnished; and resistance to wear and weather. All of these charac teristics, and some more than others, vary according to the species of wood. Although many types and species of wood used historically are no longer available, wood selection and construction practices have always capitalized on its attributes and compensated for it is weaknesses. Their resistance to decay made white oak and cedar common choices for roofing shingles, while oak and maple were frequently chosen for flooring because of their hardness. Pine and yellow poplar have often been used for siding and trim because of their straight grain and ease of milling, but they must be painted to protect them from decay.

Plywood is an engineered product formed by laminating thin sheets of wood together; it was introduced to the U.S. building industry in the early 20th century. Because plywood has greater structural potential than wood, and as a sheet can be installed more efficiently, it soon replaced boards as sheathing before being replaced itself by less-expensive particle board for many applications. By applying surface veneers and adhesives, plywood can also be used as siding or for fine interior finishes on paneling or cabinetry. Glued lami nated timber (glulam), first manufactured in the 1930s, is another engineered wood material. It is an important material in mid-20th century buildings and often used for massive arches and trusses in sports arenas and similar large, open, column-free spaces.

Many historic buildings have wood structural systems and features, such as stairs or columns. The majority of both practical and decora tive features, particularly on the interior, are made of wood, such as flooring and paneling.

Metals Metal features—including steps, porches, railings, balconies, and entire facades; cornices, siding, cladding, roofs, roof cresting, and storefronts; and doors, window sash, entablatures, and hardware— are often highly decorative as well as practical and are important in defining the overall character of historic American buildings.

Metals commonly used in historic buildings include lead, tinplate, terneplate, zinc, copper, bronze, brass, iron, steel, aluminum, stainless steel, and a variety of other alloys. Historic metal building compo nents were often designed by highly-skilled artisans. By the late 19th century, many of these components were prefabricated and available from catalogues in standardized sizes and designs.

Wrought iron is the form in which iron was first used in America. In the beginning, most wrought-iron architectural elements were small, such as nails, tie rods, straps, and hardware. Wrought-iron features gradually increased in size to include balconies, railings, porches, steps, and fencing. It was not used for structural components until around the mid 19th century, when manufacturing equipment became more sophisticated. Cast iron was initially imported from England. Although there were some iron-casting works established before the Revolution, by the early 19th century production had expanded to make a variety of cast-iron features. Structural cast-iron columns were first used in the 1820s, and cast-iron building fronts and decorative structural and ornamental features followed soon after. Cast and wrought iron are often used on the interior of historic buildings as both structural and decorative features, such as columns, staircases, railings, and light fixtures.

Steel, which is an alloy of iron and usually carbon, increased in popularity as manufacturing processes and production improved in the mid-19th century. Structural steel played an important role in the development of high-rise buildings and the skyscraper.

Lead was first used in historic buildings for roofing. Tinplate or terneplate, which was made by applying a lead and tin coating to sheet metal or steel, became a common roofing material after it was first produced in the 1820s. (Pure tin was rarely used as a building material because it is so soft.) The application of a zinc coating on sheet metal created galvanized iron, which was used for roofing and decorative roofing features, such as steeples and roof cresting, as well as other ornamental architectural features, such as door and window hood molds, lintels, and oriel and bay windows. Prefabri cated Quonset huts constructed of corrugated galvanized steel began to be manufactured during World War II for the military on the battlefield for housing, storage, and other uses.

Entire pressed-metal and galvanized-iron storefronts and individual decorative features were manufactured to simulate wood, stone, or cast iron from the latter part of the 19th century into the early years of the 20th century. Copper roofs were installed on many public buildings from the 1790s through the first quarter of the 19th cen tury. Copper continues to be used, often for porch roofs as well as gutters, downspouts, and flashing. Bronze and brass are both alloys of copper. Bronze, which weathers well, appears as entrance doors and historic storefronts. Brass, usually polished, is used for deco rative interior features, such as grilles and elevator doors. Nickel, when employed as a building component, is in the form of an alloy, usually nickel silver, Monel, or some stainless steel. In comparison to other construction metals, stainless steel is quite new, essentially only coming into use in the 1920s when it became a favorite material for Art Deco-style buildings.

Aluminum—lightweight and corrosion-resistant—was not utilized much in buildings because it was so expensive until the 1920s, when expanded production reduced its cost. Aluminum siding, which was advertised as maintenance free, became a popular siding material for single-family residences after it was introduced in the late 1930s.

Some of the uses of aluminum include roofing and roofing features, such as gutters, downspouts, and flashing, as well as windows and storefront surrounds.

Porcelain enamel, or vitreous enamel, is composed of a thin coating of glass fused to cast-iron or steel sheets, panels, tiles, or shingles.

Although developed in the late 19th century, it was not commonly used in buildings until the late 1920s and 1930s for Art Deco and Art Moderne storefronts. Lustron houses, constructed of prefabricated, enameled steel panels and intended for mass production, were introduced in the late 1940s in anticipation of the need for housing after the war. These houses were promoted for their low mainte nance, in part because the walls, ceilings, and other interior surfaces were also enameled steel panels and easily washable.

Glass For centuries, only blown cylinder and crown glass in small pieces was available and it was expensive. Thus, the glass in early windows in American buildings consisted of small panes which gradually increased in size over the years. With the invention of cast plate glass in 1848, large plates of glass could be manufactured which were strong and inexpensive. Plate glass was first used in the early 1850s as the primary exterior material (with a cast-iron framework) for such structures as international exhibition buildings, worlds’ fair pavilions, and greenhouses and conservatories. In the early 20th century, architects began using glass curtain walls in Art Moderne style architecture and, most notably, the International Style.

Tempered glass is a hardened or toughened glass which began to be used in building construction around 1940. By the middle of the 20th century, glass as a cladding system became synonymous with curtain wall systems.

In addition to clear glass—flat or sometimes curved—there is also stained glass, tinted, patterned, textured, etched, frosted, leaded, painted, colored opaque glass and spandrel glass, prism glass, deco rative Val de Verre glass (colored art glass), ceramic frit (pigmented glass enamel fused to a glass surface), and glass block. Many of these types of glass can be found in windows, transoms, doors and entrances, and storefront display windows, whereas some of them— especially opaque, pigmented structural glass with trade names such as Vitrolite, Carrara Glass, and Sani Onyx—are more likely to appear as exterior cladding on Art Deco-style or Art Moderne storefronts.

Spandrel glass was first introduced on mid-20th-century buildings, particularly in storefront and curtain wall systems. Glass was also used historically in skylights and monitors; in theater, hotel, and apartment building marquees and canopies; and as a component of lightning rods and weathervanes, address plates, and signage.

Glass features on the interior of historic buildings include transoms, windows, privacy screens, office dividers, wall partitions for bor rowed light in office corridors, teller windows in banks, ticket win dows in train stations and movie theaters, doorknobs, light fixtures, mirrored wall inlay, and also, beginning in the latter part of the 20th century, wall mosaics. Pigmented structural glass can be found in bathrooms and some kitchens because of its sanitary qualities.

Low-e (low emissivity) glass, which is primarily used in windows to minimize solar gain, was developed in the last quarter of the 20th century. Impact-resistant glass is another more-recently developed type of glass designed to withstand hurricane-force wind and which can also be installed as a blast-resistant security feature.

Paint and Other Coatings Paints and paint-like coatings have been used on historic buildings in America as protective coatings and for decorative treatments.

What is commonly considered to be paint is a liquid consisting of a pigment which makes it opaque and colors it, a binder or base to hold it together, and sometimes a vehicle to carry the pigment.

Many historic paints contained lead in the form of lead white, included as a “concealing” pigment that provided opacity, although zinc oxide was also used as an alternative. Lead increased durability and prevented mold and mildew. Titanium dioxide was sometimes used as a substitute for lead in the early 20th century, but lead continued to be an ingredient in most paints until it was banned as a hazardous substance in the U.S. in 1978. Traditional paints had an oil base, usually linseed, and the earliest paint colors were, for the most part, derived from natural pigments. Like today, both glossy and flat (or matte-finish) paints were used historically on the exterior and the interior of a building. After 1875, factory-made paints were readily available. Masonry and wood stains are tradi tional coatings which also consist of a pigment, a solvent, and little, if any, binder. They have a flat finish and are transparent rather than opaque so that the substrate is still visible.

Other historic paints, such as whitewash, are water based and have a flat finish. In addition to water, whitewash is composed of hydrated (slaked) lime, salt, and various other materials and some times includes a natural pigment. Whitewash was used on interior plaster, in cellars, and on wood structural components, but not on wood doors, windows, or trim because its flat finish easily rubs off.

Whitewash was also used on the exterior of brick or stone build ings, wood fences, and farm outbuildings as a protective coating.

Often it was reapplied on an annual basis when it got dirty or if it wore off due to exposure to the weather. Calcimine (or kalsomine) and distemper paints were also water based and included natural glues, gelatin, gums, and whiting to which colored pigments could be added. They were used only on the interior and usually on plaster surfaces. Casein is a milk-based paint composed of hydrated lime, pigment, often oil, and a variety of additives to increase its durability. It was used on both the exterior and the interior of buildings.

The interiors of historic buildings can exhibit a multitude of deco rative painted treatments. Marbleized and grained finishes were applied to wood, stone, and plaster to give them the appearance of more exotic and costly materials. Other interior painted treat ments, such as murals and stencils, are purely decorative. Tempera and gouache are traditional water-based paints used almost exclu sively for decorative painting.

Experimentation that began early in the 20th century resulted in the development of acrylic water-based paint, commonly known as latex paint. Oil-based/alkyd paint continues to be used in the 21st century and is still preferred for certain applications. Latex paint tends to be more popular not only because it is water-based (making clean up easy during and after painting), but it also has fewer toxic vapors and, like solvent-based oil/alkyd paints, is very durable.

Varnish, which is used primarily on interior wood features but also on exterior entrance doors, is another traditional coating. Unlike paint, varnish is transparent, composed of a resin, a drying oil, and a solvent. It has a glossy finish, which dulls over time.

Composite Materials: Plastic, Resin, and Vinyl; Fiber-Reinforced Cement Siding; Fiberboard; and Floor Coverings Plastic is a malleable material composed of synthetic or natural organic materials made from various organic polymers, such as polyethylene and polyvinyl chloride (PVC), which can be poured into molds or rolled in sheets. It is generally agreed that the term plastic was introduced into popular usage in 1907 to describe the first fully synthetic plastic. Improved plastics were available in America by World War I.

Production soared during World War II because plastics were needed to make up for the shortage of other materials. In mass production by the 1950s, the industry continued to expand with the development of increasingly more sophisticated plastics.

Vinyl siding came on the market in the late 1950s, and its use, primarily in residential construction, increased as the product improved over the years. Coating canvas awnings with vinyl helped to extend their lifespan, evolving, even tually, into awnings manufactured solely of vinyl. Plastic signs on the exterior of historic commercial buildings changed and radically expanded the role of signage as advertising as well as being impor tant design features themselves. Plastic was used sometimes for decorative trim on storefronts. Vinyl-coated wallpaper was used as early as the 1920s and is still selected for restaurants, commercial spaces, and hospitals because it is durable and washable. Other plastic materials became popular in the 1950s in the form of plastic-laminate sheeting and wall tiles.

Fiber-reinforced plastic (FRP), is made of a polymer matrix mixed with fiber, usually fiberglass, to add strength; it is noted for its ability to be molded in thin shells. FRP is sometimes used as a substitute material to recreate missing or deteriorated architectural features in historic buildings. Acrylic plastic is a transparent synthetic plastic, generally identified by one of its trade names—Plexiglass or Lucite— which was patented in the 1950s as an alternative to glass. Foamed polystyrene, better known as Styrofoam, was first used in the mid 1950s as building insulation.

Fiber-Reinforced Cement Siding is a composite material made of sand, cement, and cellulose fibers. It was developed in the latter part of the 20th century as a less-hazardous replacement for asbestos cement siding, which preceded it, and was used for siding and roof ing shingles from the early 20th century to the 1970s. Fiber-rein forced cement siding is frequently installed in the form of horizontal boards or vertical panels as exterior siding. Fiber-reinforced cement is used on both residential and commercial buildings.

Fiberboard is a composite hardboard material made from pressure-molded wood fibers. It had early precedents in the late 18th century, but was first manufactured in large quantities in the 1920s, with its use expanding in the 1930s and 40s. Fiberboard (or wallboard, as it is commonly known) was marketed by various companies, such as Masonite. It was used as sheathing for roofing and siding on the exterior, for insulation, and for interior walls.

The first composite floor covering was Linoleum, made from oxi dized linseed oil and ground cork or wood flour. Its manufacture in the U.S. began in the late 19th century, about the same time syn thetic rubber floor tile was also introduced. Asphalt floor tiles were first used in the 1920s and remained popular into the 1950s. Plastic/ vinyl replaced asphalt as a binder in floor tiles in the late 1920s, in part because plastic, unlike asphalt, could be made in lighter colors and a greater variety of colors. Semi-flexible vinyl flooring, manu factured in the form of tiles or rolled sheets, was developed by the 1930s. After the war, it became more affordable and frequently was chosen for both residential and commercial interiors.

Imitative Materials Imitative building materials are generally common and readily avail able materials used to simulate a more expensive material. They have a long history in American building construction. Wood, cut and planed and sometimes coated with a sand paint, has been used since the 18th century to replicate cut blocks of stone and quoins on the exterior of a building. Stucco, applied over any kind of construc tion (from log to rubble masonry) and scored to resemble stone, could make even a log house look elegant. Cast iron and pressed metal, whether as a complete façade, a storefront, or an individual feature such as a window hood, cornice, or decorative pilaster, were also used on the exterior of buildings to replicate stone. Not only architectural terra cotta, but cast stone served as a substitute for stone. Metal and concrete roofing tiles were used as less-costly alter natives to clay roofing tiles.

In the 20th century, the use of exterior imitative materials expanded as new products were developed. Asphalt roll siding that resembled brick could be applied to a wood building, and asbestos composite shingles were produced to replace not only wood shingle siding, but also slate roofing shingles. Aluminum siding has been used as a replacement for wood siding, followed by vinyl siding, pressed wood siding, and, more recently, composite or fiber-cement siding. Manu factured faux slate roofing became popular because it costs less than slate and is lighter weight. Over the years, imitative materials have increased in variety as synthetic materials continue to be intro duced, including a substitute, an exterior insulation and finish system (EIFS), for another imitative material—stucco. Imitative materials are also used to recreate missing or deteriorated architectural fea tures in historic buildings.

On the interior, imitative materials, such as scored plaster, were his torically applied to walls to give the appearance of stone. Painted or marbleized finishes on plaster or wood could further simulate stone, and decorative graining could transform the surface of a common wood into a more exotic species. Scagliola, which is often applied to brick columns, is a very old technique that uses a plaster-like com posite material to simulate marble. Lincrusta, an embossed wall covering, was developed in the late 19th century to simulate pressed metal. Embossed wall coverings continue to be produced in the 21st century. Concrete, vinyl, and other manufactured flooring materials are designed in many patterns and colors to replicate brick, stone, clay tile, and wood.

Roofs The roof—with its form; features such as cresting, dormers, cupo las, and chimneys; and the size, color, and patterning of the roofing material—is an important design element of many historic buildings.

In addition, a weathertight roof is essential to the long-term preser vation of the entire structure. Historic roofing reflects availability of materials, levels of construction technology, climate, and cost.

Throughout all periods of American history, with only minor excep tion, wood has been used for roofing; despite the early use of many other materials, wood shingles remained the most common roofing material throughout much of the 19th century. Initially the species of wood used would have been specific to a region, but the quality and design of a building were usually the prime determinants in the way wood was used, ranging from wide, lapped boards to small, uniform, geometrically-shaped shingles.

Clay tile was used at least in a limited way in the first settlements on the East coast and it was manufactured in America by the mid 17th century. The Spanish influence in the use of clay roof ing tiles is apparent in buildings in the south, southwest, and western parts of the country.

Slate was also an early roofing material, but it was imported until the end of the 18th century when the first slate quarry opened. Both slate and tile roofs provided fire protection, especially important in urban areas. The use of slate expanded quickly in the second half of the 19th century with the development of the railroads, and it remained a preferred roofing material until the middle of the 20th century.

Lead and copper were the first metals used for roofing, later joined by zinc and iron in the beginning of the 19th century. Lead was used in the mid 19th century for flashing and sometimes for the roofs of bay windows, domed, or steeply-pitched sections of a larger roof, and…