Standards Guidelines.pdf

The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating

Restoring &Reconstructing Historic Buildings

The Secretary of the Interior is responsible for establishing professional standards and providing advice on the preservation and protection of all cultural resources listed in or eligible for listing in the National Register of Historic Places. The Secretary of the Interior’s Standards for the Treatment of Historic Properties, apply to all proposed development grant-in-aid projects assisted through the National Historic Preservation Fund, and are intended to be applied to a wide variety of resource types, including buildings, sites, structures, objects, and districts. They 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 replace the 1978 and 1983 versions of 36 CFR 68 entitled, “The Secretary of the Interior’s Standards for Historic Preservation Projects.” The Guidelines in this book also replace the Guidelines that were published in 1979 to accompany the earlier Standards.

Please note that The Secretary of the Interior’s Standards for the Treatment of Historic Properties are only regulatory for projects receiving federal grant-in-aid funds; otherwise, the Standards and Guidelines are intend-ed only as general guidance for work on any historic building.

Finally, another regulation, 36 CFR Part 67, focuses on “certified historic structures” as defined by the IRS Code of 1986. The “Standards for Rehabilitation” cited in 36 CFR 67 should always be used when property owners are seek-ing certification for Federal tax benefits.

Library of Congress Cataloging-in-Publication Data

Weeks, Kay D.

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.

p. cm.

ISBN 0-16-048061-2

1. Architecture--United States--Conservation and restoration--Standards. 2. Historic buildings--United States--Conservation and restoration--Standards. I. Grimmer, Anne E.

II. United States, National Park Service. Preservation Assistance Division. III. Title.

NA106.W44 1995 95-23913

720".28"8021873--dc20 CIP

Rev.

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

U.S. Department of the Interior National Park Service Cultural Resource Stewardship and Partnerships Heritage Preservation Services Washington, D.C.

Contents

Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Introduction

Choosing an Appropriate Treatment for the Historic Building

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

Historical Overview: Building Materials • Building Features • Site • Setting • Special Requirements

Standards for Preservation and Guidelines for Preserving Historic Buildings

Introduction

Building Exterior: Materials Masonry Wood Architectural Metals

Building Exterior: Features Roofs Windows Entrances and Porches Storefronts

Building Interior Structural Systems Spaces, Features, and Finishes Mechanical Systems

Building Site

Setting (District/Neighborhood)

Special Requirements Energy Efficiency Accessibility Considerations Health and Safety Considerations i

Standards for Rehabilitation and Guidelines for Rehabilitating Historic Buildings

Introduction

Building Exterior: Materials Masonry Wood Architectural Metals

Building Exterior: Features Roofs Windows Entrances and Porches Storefronts

Building Interior Structural Systems Spaces, Features, and Finishes Mechanical Systems

Building Site

Setting (District/Neighborhood)

Special Requirements Energy Efficiency New Additions to Historic Buildings Accessibility Considerations Health and Safety Considerations

Standards for Restoration and Guidelines for Restoring Historic Buildings

Introduction

Building Exterior: Materials Masonry Wood Architectural Metals ii

Building Exterior: Features Roofs Windows Entrances and Porches Storefronts

Building Interior Structural Systems Spaces, Features, and Finishes Mechanical Systems

Building Site

Setting (District/Neighborhood)

Special Requirements Energy Efficiency Accessibility Considerations Health and Safety Considerations

Standards for Reconstruction and Guidelines for Reconstructing Historic Buildings

Introduction

Research and Documentation

Building Exterior

Building Interior

Building Site

Setting (District/Neighborhood)

Special Requirements Energy Efficiency Accessibility Considerations Health and Safety Considerations

Technical Guidance Publications iii

Photo Credits Front and Back Covers

Bangor House, Bangor, Maine, circa 1880. Historic photo (front) and drawing (back): Courtesy, Maine State Historic Preservation Office.

Historical Overview (Materials and Features)

Building Exterior: Masonry. Jack E. Boucher, HABS.

Building Exterior: Wood. Jack E. Boucher, HABS.

Building Exterior: Architectural Metals. Cervin Robinson, HABS.

Building Exterior: Roofs. Jack E. Boucher, HABS.

Building Exterior: Windows. Jack E. Boucher, HABS.

Building Exterior: Entrances and Porches. Jack E. Boucher, HABS.

Building Exterior: Storefronts. Jack E. Boucher, HABS.

Building Interior: Structural Systems. Cervin Robinson, HABS.

Building Interior: Spaces, Features and Finishes. Brooks Photographers, HABS Collection.

Building Interior: Mechanical Systems. National Park Service Files.

Building Site. Jack E. Boucher, HABS.

Setting (District/Neighborhood). Charles Ashton.

Energy Conservation. Laura A. Muckenfuss.

New Additions to Historic Buildings. Rodney Gary.

Accessibility Considerations. Department of Cultural Resources, Raleigh, North Carolina.

Health and Safety Considerations. National Park Service Files.

iv

Chapter Heads

Preservation Hale House, Los Angeles, California. Photos: Before: National Park Service files; After: Bruce Boehner.

Rehabilitation Storefront, Painted Post, New York, after rehabilitation. Photo: Kellogg Studio.

Restoration Camron-Stanford House, Oakland, California. Photos: Before: National Park Service files; After: Courtesy, James B. Spaulding.

Reconstruction George Washington Memorial House at Washington Birthplace National Monument, Westmoreland County, Virginia.

Photo: Richard Frear.

Text

It should be noted that those photographs used to illustrate the guidelines text that are not individually credited in the captions are from National Park Service files.

Acknowledgements

The Standards for the Treatment of Historic Properties, published in 1992, were reviewed by a broad cross-section of government entities and private sector organizations. The Guidelines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Buildings were developed in cooperation with the National Conference of State Historic Preservation Officers and reviewed by individual State Historic Preservation Offices nationwide. We wish to thank Stan Graves and Claire Adams, in particular, for their thoughtful evaluation of the new material.

Dahlia Hernandez provided administrative support throughout the project.

Finally, this book is dedicated to H. Ward Jandl, whose long-term commitment to historic preservation helped define the profession as we know it today.

v vi

Historic Resource Types & Examples

Building: houses, barns, stables, sheds, garages, court-houses, city halls, social halls, commercial buildings, libraries, factories, mills, train depots, hotels, theaters, sta-tionary mobile homes, schools, stores, and churches.

Site: habitation sites, funerary sites, rock shelters, village sites, hunting and fishing sites, ceremonial sites, petro-glyphs, rock carvings, ruins, gardens, grounds, battlefields, campsites, sites of treaty signings, trails, areas of land, shipwrecks, cemeteries, designed landscapes, and natural features, such as springs and rock formations, and land areas having cultural significance.

Structure: bridges, tunnels, gold dredges, firetowers, canals, turbines, dams, power plants, corn-cribs, silos, roadways, shot towers, windmills, grain elevators, kilns, mounds, cairns, palisade fortifications, earthworks, rail-road grades, systems of roadways and paths, boats and ships, railroad locomotives and cars, telescopes, carousels, bandstands, gazebos, and aircraft.

Object: sculpture, monuments, boundary markers, statu-ary, and fountains.

District: college campuses, central business districts, resi-dential areas, commercial areas, large forts, industrial com-plexes, civic centers, rural villages, canal systems, collec-tions of habitation and limited activity sites, irrigation sys-tems, large farms, ranches, estates, or plantations, trans-portation networks, and large landscaped parks.

(Sidebar adapted from National Register Property and Resource Types, p. 15, National Register Bulletin 16A, How to Complete the National Register Form, published by the National Register Branch, Interagency Resources Division, National Park Service, U.S.

Department of the Interior, 1991.)

The Secretary of the Interior’s Standards for the Treatment of Historic Properties may be applied to one historic resource type or a variety of historic resource types; for example, a project may include a complex of buildings such as a house, garage, and barn; the site, with a designed landscape, natural features, and archeological components; structures such as a system of roadways and paths or a bridge; and objects such as fountains and statuary.

Zoar Historic District, Ohio. Aerial view. Photo: National Park Service.

Elmendorf, Lexington, Kentucky. Photo: Charles A. Birnbaum.

Introduction

Choosing an Appropriate Treatment for the Historic Building

The Standards are neither technical nor prescriptive, but are intended to promote responsible preservation practices that help protect our 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 provide philo-sophical consistency to the work.

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

Relative importance in history. Is the building a nationally significant resource—a rare survivor or the work of a master architect or craftsman? Did an important event take place in it? National Historic Landmarks, designated for their “exceptional signifi-cance in American history,” or many buildings indi-vidually listed in the National Register often warrant Preservation or Restoration. Buildings that con-tribute to the significance of a historic district but are not individually listed in the National Register more frequently undergo Rehabilitation for a compatible new use.

Physical condition. What is the existing condition— or degree of material integrity—of the building prior to work? Has the original form survived largely intact or has it been altered over time? Are the alterations an important part of the building’s history?

Preservation may be appropriate if distinctive materi-als, features, and spaces are essentially intact and con-vey the building’s historical significance. If the build-ing requires more extensive repair and replacement, or if alterations or additions are necessary for a new use, then Rehabilitation is probably the most appro-priate treatment. These key questions play major roles in determining what treatment is selected.

Proposed use. An essential, practical question to ask is: Will the building be used as it was historically or will it be given a new use? Many historic buildings can be adapted for new uses without seriously damag-ing their historic character; special-use properties such as grain silos, forts, ice houses, or windmills may be extremely difficult to adapt to new uses without major intervention and a resulting loss of historic character and even integrity.

Mandated code requirements. Regardless of the treatment, code requirements will need to be taken into consideration. But if hastily or poorly designed, a series of code-required actions may jeopardize a building’s materials as well as its historic character.

Thus, if a building needs to be seismically upgraded, modifications to the historic appearance should be minimal. Abatement of lead paint and asbestos with-in historic buildings requires particular care if impor-tant historic finishes are not to be adversely affected.

Finally, alterations and new construction needed to meet accessibility requirements under the Americans with Disabilities Act of 1990 should be designed to minimize material loss and visual change to a historic building.

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

The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring and Reconstructing Historic Buildings are intended to provide guidance to historic building owners and building managers, preservation consultants, archi-tects, contractors, and project reviewers prior to treat-ment.

As noted, while the treatment Standards are designed to be applied to all historic resource types included in the National Register of Historic Places—buildings, sites, structures, districts, and objects—the Guidelines apply to specific resource types; in this case, buildings.

The Guidelines have been prepared to assist in apply-ing the Standards to all project work; consequently, they are not meant to give case-specific advice or address exceptions or rare instances. Therefore, it is recommended that the advice of qualified historic preservation professionals be obtained early in the planning stage of the project. Such professionals may include architects, architectural historians, historians, historical engineers, archeologists, and others who have experience in working with historic buildings.

The Guidelines pertain to both exterior and interior work on historic buildings of all sizes, materials, and types. 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” col-umn on the right.

One chapter of this book is devoted to each of the four treatments: Preservation, Rehabilitation, Restoration, and Reconstruction. Each chapter con-tains one set of Standards and accompanying Guidelines that are to be used throughout the course of a project. The Standards for the first treatment, Preservation, require retention of the greatest amount of historic fabric, along with the building’s historic form, features, and detailing as they have evolved over time. 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. The Restoration Standards allow for the depiction of a building at a particular time in its history by preserving materials from the period of sig-nificance and removing materials from other periods.

The Reconstruction Standards establish a limited framework for re-creating a vanished or non-surviv-ing building with new materials, primarily for inter-pretive purposes.

The Guidelines are preceded by a brief historical overview of the primary historic building materials (masonry, wood, and architectural metals) and their diverse uses over time. Next, building features com-prised of these materials are discussed, beginning with the exterior, then moving to the interior. Special requirements or work that must be done to meet accessibility requirements, health and safety code requirements, or retrofitting to improve energy effi-ciency are also addressed here. Although usually not part of the overall process of protecting historic build-ings, this work must also be assessed for its potential impact on a historic building.

Historical Overview Building Exterior Materials

Masonry

Stone is one of the more lasting of masonry building materials and has been used throughout the history of American building construction. The kinds of stone most commonly encountered on historic buildings in the U.S. include various types of sandstone, lime-stone, marble, granite, slate and fieldstone. Brick var-ied considerably in size and quality. Before 1870, brick clays were pressed into molds and were often unevenly fired. The quality of brick depended on the type of clay available and the brick-making tech-niques; by the 1870s—with the perfection of an extrusion process—bricks became more uniform and durable. Terra cotta is also a kiln-dried clay product popular from the late 19th century until the 1930s.

The development of the steel-frame office buildings in the early 20th century contributed to the wide-spread use of architectural terra cotta. Adobe, which consists of sun-dried earthen bricks, was one of the earliest building 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. By the latter part of the 19th century, portland cement was usually added resulting in a more rigid and non-absorbing mortar. Like historic mortar, early stucco coatings were also heavily lime-based, increasing in hardness with the addition of portland cement in the late 19th century. Concrete has a long history, being variously made of tabby, volcanic ash and, later, of natural hydraulic cements, before the introduction of portland cement in the 1870s. Since then, concrete has also been used in its precast form.

While masonry is among the most durable of historic building materials, it is also very susceptible to dam-age by improper maintenance or repair techniques and harsh or abrasive cleaning methods.

Wood

Wood has played a central role in American building during every period and in every style. Whether as structural members, exterior cladding, roofing, interi-or finishes, or decorative features, wood is frequently an essential component of historic buildings.

Because it can be easily shaped by sawing, sanding, planing, carving, and gouging, wood is used for architectural features such as clapboard, cornices, brackets, entablatures, shutters, columns and balustrades. These wooden features, both functional and decorative, are often important in defining the historic character of the building.

Architectural Metals

Architectural metal features—such as cast iron facades, porches, and steps; sheet metal cornices, sid-ing, roofs, roof cresting and storefronts; and cast or rolled metal doors, window sash, entablatures, and hardware—are often highly decorative and may be important in defining the overall character of historic American buildings.

Metals commonly used in historic buildings include lead, tin, zinc, copper, bronze, brass, iron, steel, and to a lesser extent, nickel alloys, stainless steel and alu-minum. Historic metal building components were often created by highly skilled, local artisans, and by the late 19th century, many of these components were prefabricated and readily available from catalogs in standardized sizes and designs.

Building Exterior Features

Roofs

The roof—with its shape; features such as cresting, dormers, cupolas, and chimneys; and the size, color, and patterning of the roofing material—is an impor-tant design element of many historic buildings. In addition, a weathertight roof is essential to the longterm preservation of the entire structure.

Historic roofing reflects availability of materials, levels of construction technology, weather, and cost.

Throughout the country in all periods of history, wood shingles have been used—their size, shape, and detailing differing according to regional craft prac-tices.

European settlers used clay tile for roofing at least as early as the mid-17th century. In some cities, such as New York and Boston, clay tiles were popularly used as a precaution against fire. The Spanish influence in the use of clay tiles is found in the southern, south-western and western states. In the mid-19th century, tile roofs were often replaced by sheet-metal, which is lighter and easier to maintain.

Evidence of the use of slate for roofing dates from the mid-17th century. Slate has remained popular for its durability, fireproof qualities, and its decorative appli-cations. The use of metals for roofing and roof fea-tures dates from the 18th century, and includes the use of sheet metal, corrugated metal, galvanized metal, tin-plate, copper, lead and zinc.

New roofing materials developed in the early 20th century include built-up roll roofing, and concrete, asbestos, and asphalt shingles.

Windows

Technology and prevailing architectural styles have shaped the history of windows in the United States starting in the 17th century with wooden casement windows with tiny glass panes seated in lead cames.

From the transitional single-hung sash in the early 1700s to the true double-hung sash later in the cen-tury, these early wooden windows were characterized by small panes, wide muntins, and decorative trim.

As the sash thickness increased, muntins took on a thinner appearance as they narrowed in width but increased in thickness.

Changes in technology led to larger panes of glass so that by the mid-19th century, two-over-two lights were common; the manufacture of plate glass in the United States allowed for use of large sheets of glass in commercial and office buildings by the late 19th cen-tury. With mass-produced windows, mail order dis-tribution, and changing architectural styles, it was possible to obtain a wide range of window designs and light patterns in sash. Early 20th century designs frequently utilized smaller lights in the upper sash and also casement windows. The desire for fireproof building construction in dense urban areas con-tributed to the growth of a thriving steel window industry along with a market for hollow metal and metal clad wooden windows.

As one of the few parts of a building serving as both an interior and exterior feature, windows are nearly always an important part of a historic building.

Entrances and Porches

Entrances and porches are quite often the focus of historic buildings, particularly on primary elevations.

Together with their functional and decorative features such as doors, steps, balustrades, pilasters, and entab-latures, they can be extremely important in defining the overall character of a building. In many cases, porches were energy-saving devices, shading southern and western elevations. Usually entrances and porch-es were integral components of a historic building’s design; for example, porches on Greek Revival hous-es, with Doric or Ionic columns and pediments, echoed the architectural elements and features of the larger building. Central one-bay porches or arcaded porches are evident in Italianate style buildings of the 1860s. Doors of Renaissance Revival style buildings frequently supported entablatures or pediments.

Porches were particularly prominent features of Eastlake and Stick Style houses in which porch posts, railings, and balusters were characterized by a massive and robust quality, with members turned on a lathe.

Porches of bungalows of the early 20th century were characterized by tapered porch posts, exposed post and beams, and low pitched roofs with wide over-hangs. Art Deco commercial buildings were entered through stylized glass and stainless steel doors.

Storefronts

The earliest extant storefronts in the U.S., dating from the late 18th and early 19th centuries, had bay or oriel windows and provided limited display space.

The 19th century witnessed the progressive enlarge-ment of display windows as plate glass became avail-able in increasingly larger units. The use of cast iron columns and lintels at ground floor level permitted structural members to be reduced in size. Recessed entrances provided shelter for sidewalk patrons and further enlarged display areas. In the 1920s and 1930s, aluminum, colored structural glass, stainless steel, glass block, neon, and other new materials were introduced to create Art Deco storefronts.

The storefront is usually the most prominent feature of a historic commercial building, playing a crucial role in a store’s advertising and merchandising strate-

gy. Although a storefront normally does not extend beyond the first story, the rest of the building is often related to it visually through a unity of form and detail. Window patterns on the upper floors, cornice elements, and other decorative features should be carefully retained, in addition to the storefront itself.

Building Interior

Structural Systems

The types of structural systems found in the United States include, but are not limited to the following:

wooden frame construction (17th c.), balloon frame construction (19th c.), load-bearing masonry con-struction (18th c.), brick cavity wall construction (19th c.), heavy timber post and beam industrial con-struction (19th c.), fireproof iron construction (19th c.), heavy masonry and steel construction (19th c.), skeletal steel construction (19th c.), and concrete slab and post construction (20th c.).

If features of the structural system are exposed such as loadbearing brick walls, cast iron columns, roof truss-es, posts and beams, vigas, or stone foundation walls, they may be important in defining the building’s overall historic character. Unexposed structural fea-tures that are not character-defining or an entire structural system may nonetheless be significant in the history of building technology. The structural system should always be examined and evaluated early in the project planning stage to determine its physical condition, its ability to support any proposed changes in use, and its importance to the building’s historic character or historical significance.

Spaces, Features, and Finishes

An interior floor plan, the arrangement and sequence of spaces, and built-in features and applied finishes are individu-ally and collectively important in defining the historic charac-ter of the building. Interiors are comprised of a series of pri-mary and secondary spaces. This is applicable to all build-ings, from courthouses to cathedrals, to cottages and office buildings. Primary spaces, including entrance halls, parlors, or living rooms, assembly rooms and lobbies, are defined not only by their function, but also by their features, finishes, size and proportion.

Secondary spaces are often more functional than decorative, and may include kitchens, bathrooms, mail rooms, utility spaces, secondary hallways, firestairs and office cubicles in a commercial or office space. Extensive changes can often be made in these less important areas without having a detri-mental effect on the overall historic character.

Mechanical Systems

Mechanical, lighting and plumbing systems improved significantly with the coming of the Industrial Revolution. The 19th century interest in hygiene, personal comfort, and the reduction of the spread of disease were met with the development of central heating, piped water, piped gas, and network of underground cast iron sewers. Vitreous tiles in kitchens, baths and hospitals could be cleaned easily and regularly. The mass production of cast iron radi-ators made central heating affordable to many; some radiators were elaborate and included special warm-ing chambers for plates or linens. Ornamental grilles and registers provided decorative covers for functional heaters in public spaces. By the turn of the 20th cen-tury, it was common to have all these modern ameni-ties as an integral part of the building.

The greatest impacts of the 20th century on mechan-ical systems were the use of electricity for interior lighting, forced air ventilation, elevators for tall build-ings, exterior lighting and electric heat. The new age of technology brought an increasingly high level of design and decorative art to many of the functional elements of mechanical, electrical and plumbing sys-tems.

The visible decorative features of historic mechanical systems such as grilles, lighting fixtures, and orna-mental switchplates may contribute to the overall his-toric character of the building. Their identification needs to take place, together with an evaluation of their physical condition, early in project planning.

On the other hand, mechanical systems need to work efficiently so many older systems, such as compressors and their ductwork, and wiring and pipes often need to be upgraded or entirely replaced in order to meet modern requirements.

Building Site

The building site consists of a historic building or buildings, structures, and associated landscape fea-tures within a designed or legally defined parcel of land. A site may be significant in its own right, or because of its association with the historic building or buildings. The relationship between buildings and landscape features on a site should be an integral part of planning for every work project.

Setting (District/Neighborhood)

The setting is the larger area or environment in which a historic property is located. It may be an urban, suburban, or rural neighborhood or a natural landscape in which buildings have been constructed.

The relationship of buildings to each other, setbacks, fence patterns, views, driveways and walkways, and street trees together create the character of a district or neighborhood.

Special Requirements

Work that must be done to meet accessibility require-ments, health and safety requirements or retrofitting to improve energy efficiency is usually not part of the over-all process of protecting historic buildings; rather, this work is assessed for its potential impact on the historic building.

Energy Efficiency

Some features of a historic building or site such as cupolas, shutters, transoms, skylights, sun rooms, porches, and plantings can play an energy-conserving role. Therefore, prior to retrofitting historic build-ings to make them more energy efficient, the first step should always be to identify and evaluate existing historic features to assess their inherent energy-con-serving potential. If it is determined that retrofitting measures are appropriate, then such work needs to be carried out with particular care to ensure that the building’s historic character is retained.

Accessibility Considerations

It is often necessary to make modifications to a his-toric building so that it will be in compliance with current accessibility code requirements. Accessibility to certain historic structures is required by three spe-cific federal laws: the Architectural Barriers Act of 1968, Section 504 of the Rehabilitation Act of 1973, and the Americans with Disabilities Act of 1990.

Federal rules, regulations, and standards have been developed which provide guidance on how to accom-plish access to historic areas for people with disabili-ties. Work must be carefully planned and undertak-en so that it does not result in the loss of character-defining spaces, features, and finishes. The goal is to provide the highest level of access with the lowest level of impact.

Health and Safety Considerations

In undertaking work on historic buildings, it is neces-sary to consider the impact that meeting current health and safety codes (public health, occupational health, life safety, fire safety, electrical, seismic, struc-tural, and building codes) will have on character-defining spaces, features, and finishes. Special coor-dination with the responsible code officials at the state, county, or municipal level may be required.

Securing required building permits and occupancy licenses is best accomplished early in work project planning. It is often necessary to look beyond the “letter” of code requirements to their underlying pur-pose; most modern codes allow for alterative approaches and reasonable variance to achieve com-pliance.

Some historic building materials (insulation, lead paint, etc.) contain toxic substances that are poten-tially hazardous to building occupants. Following careful investigation and analysis, some form of abatement may be required. All workers involved in the encapsulation, repair, or removal of known toxic materials should be adequately trained and should wear proper personal protective gear. Finally, preven-tive and routine maintenance for historic structures known to contain such materials should also be developed to include proper warnings and precau-tions.

Standards for

Guidelines for Preserving Historic Buildings

Preservation is defined as the act or process of applying mea-sures necessary to sustain the existing form, integrity, and materials of an historic property. Work, including prelimi-nary 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. New exterior additions are not within the scope of this treatment; however, the limited and sensitive upgrading of mechanical, electrical, and plumbing systems and other code-required work to make properties functional is appropriate within a preservation project.

Standards for Preservation

1. A property will be used as it was historically, or be given a new use that maximizes the retention of dis-tinctive materials, features, spaces, and spatial relationships. Where a treatment and use have not been identified, a property will be protected and, if necessary, stabilized until additional work may be under-taken.

2. The historic character of a property will be retained and preserved. The replacement of intact or repairable historic materials or alteration of features, spaces, and spatial relationships that characterize a property will be avoided.

3. Each property will be recognized as a physical record of its time, place, and use. Work needed to stabi-lize, consolidate, and conserve existing historic materials and features will be physically and visually com-patible, identifiable upon close inspection, and properly documented for future research.

4. Changes to a property that have acquired historic significance in their own right will be retained and preserved.

5. Distinctive materials, features, finishes, and construction techniques or examples of craftsmanship that characterize a property will be preserved.

6. The existing condition of historic features will be evaluated to determine the appropriate level of inter-vention needed. Where the severity of deterioration requires repair or limited replacement of a distinctive feature, the new material will match the old in composition, design, color, and texture.

7. Chemical or physical treatments, if appropriate, will be undertaken using the gentlest means possible.

Treatments that cause damage to historic materials will not be used.

8. Archeological resources will be protected and preserved in place. If such resources must be disturbed, mitigation measures will be undertaken.

Guidelines for Preserving Historic Buildings

Introduction

In Preservation, the options for replacement are less extensive than in the treatment, Rehabilitation. This is because it is assumed at the outset that building materials and character-defining features are essential-ly intact, i.e, that more historic fabric has survived, unchanged over time. The expressed goal of the Standards for Preservation and Guidelines for Preserving Historic Buildings is retention of the building’s existing form, features and detailing. This may be as simple as basic maintenance of existing materials and features or may involve preparing a his-toric structure report, undertaking laboratory testing such as paint and mortar analysis, and hiring conser-vators to perform sensitive work such as reconstitut-ing interior finishes. Protection, maintenance, and repair are emphasized while replacement is mini-mized.

Identify, Retain, and Preserve Historic Materials and Features

The guidance for the treatment Preservation begins with recommendations to identify the form and detailing of those architectural materials and features that are important in defining the building’s historic character and which must be retained in order to pre-serve that character. Therefore, guidance on identify-ing, retaining, and preserving character-defining fea-tures is always given first. The character of a historic building may be defined by the form and detailing of exterior materials, such as masonry, wood, and metal;

exterior features, such as roofs, porches, and windows;

interior materials, such as plaster and paint; and inte-rior features, such as moldings and stairways, room configuration and spatial relationships, as well as structural and mechanical systems; and the building’s site and setting.

Stabilize Deteriorated Historic Materials and Features as a Preliminary Measure

Deteriorated portions of a historic building may need to be protected thorough preliminary stabilization measures until additional work can be undertaken.

Stabilizing may include structural reinforcement, weatherization, or correcting unsafe conditions.

Temporary stabilization should always be carried out in such a manner that it detracts as little as possible from the historic building’s appearance. Although it may not be necessary in every preservation project, stabilization is nonetheless an integral part of the treatment Preservation; it is equally applicable, if cir-cumstances warrant, for the other treatments.

Protect and Maintain Historic Materials and Features

After identifying those materials and features that are important and must be retained in the process of Preservation work, then protecting and maintaining them are addressed. Protection generally involves the least degree of intervention and is preparatory to other work. For example, protection includes the maintenance of historic materials through treatments such as rust removal, caulking, limited paint removal, and re-application of protective coatings; the cyclical cleaning of roof gutter systems; or installation of fenc-ing, alarm systems and other temporary protective measures. Although a historic building will usually require more extensive work, an overall evaluation of its physical condition should always begin at this level.

Repair (Stabilize, Consolidate, and Conserve) Historic Materials and Features

Next, when the physical condition of character-defining materials and features requires additional work, repairing by stabilizing, consolidating, and conserving is recommended. Preservation strives to retain existing materials and features while employing as little new material as possible. Consequently, guid-ance for repairing a historic material, such as masonry, again begins with the least degree of intervention pos-sible such as strengthening fragile materials through consolidation, when appropriate, and repointing with mortar of an appropriate strength. Repairing masonry as well as wood and architectural metal features may also include patching, splicing, or otherwise reinforc-ing them using recognized preservation methods.

Similarly, within the treatment Preservation, portions of a historic structural system could be reinforced using contemporary materials such as steel rods. All work should be physically and visually compatible, identifiable upon close inspection and documented for future research.

Limited Replacement In Kind of Extensively Deteriorated Portions of Historic Features

If repair by stabilization, consolidation, and conserva-tion proves inadequate, the next level of intervention involves the limited replacement in kind of extensively deteriorated or missing parts of features when there are surviving prototypes (for example, brackets, dentils, steps, plaster, or portions of slate or tile roofing). The replacement material needs to match the old both physically and visually, i.e., wood with wood, etc.

Thus, with the exception of hidden structural rein-forcement and new mechanical system components, substitute materials are not appropriate in the treat-ment Preservation. Again, it is important that all new material be identified and properly documented for future research.

If prominent features are missing, such as an interior staircase, exterior cornice, or a roof dormer, then a Rehabilitation or Restoration treatment may be more appropriate.

This three-part drawing shows the evolution of a farm house over time. Such change is part of the history of the place and is respected within the treatment, Preservation. Drawing: Center for Historic Architecture and Engineering, University of Delaware (adapted from Preservation Brief 35: Understanding Old Buildings).

circa 1760 circa 1800 circa 1850

Energy Efficiency/Accessibility Considerations/Health and Safety Code Considerations

These sections of the Preservation guidance address work done to meet accessibility requirements and health and safety code requirements; or limited retro-fitting measures to improve energy efficiency.

Although this work is quite often an important aspect of preservation projects, it is usually not part of the overall process of protecting, stabilizing, conserving, or repairing character-defining features; rather, such work is assessed for its potential negative impact on the building’s character. For this reason, particular care must be taken not to obscure, damage, or destroy character-defining materials or features in the process of undertaking work to meet code and energy requirements.

Preservation as a Treatment. When the property’s dis-tinctive materials, features, and spaces are essentially intact and thus convey the historic significance without extensive repair or replacement; when depiction at a particular period of time is not appropriate; and when a continuing or new use does not require additions or extensive alterations, Preservation may be considered as a treatment. Prior to undertaking work, a documen-tation plan for Preservation should be developed.

22 Building Exterior Masonry

Recommended

Identifying, retaining, and preserving masonry features that are important in defining the overall historic character of the building such as walls, brackets, railings, cornices, window architraves, door pediments, steps, and columns; and details such as tooling and bonding patterns, coatings, and color.

Stabilizing deteriorated or damaged masonry as a preliminary measure, when necessary, prior to undertaking appropriate preservation work.

Protecting and maintaining masonry by providing proper drainage so that water does not stand on flat, horizontal sur-faces or accumulate in curved decorative features.

Cleaning masonry only when necessary to halt deterioration or remove heavy soiling.

Carrying out masonry surface cleaning tests after it has been determined that such cleaning is appropriate. Tests should be observed over a sufficient period of time so that both the immediate and the long range effects are known to enable selection of the gentlest method possible.

Not Recommended

Altering masonry features which are important in defining the overall historic character of the building so that, as a result, the character is diminished.

Replacing historic masonry features instead of repairing or replacing only the deteriorated masonry.

Applying paint or other coatings such as stucco to masonry that has been historically unpainted or uncoated.

Removing paint from historically painted masonry.

Changing the type of paint or coating or its color.

Failing to stabilize deteriorated or damaged masonry until additional work is undertaken, thus allowing further damage to occur to the historic building.

Failing to evaluate and treat the various causes of mortar joint deterioration such as leaking roofs or gutters, differential set-tlement of the building, capillary action, or extreme weather exposure.

Cleaning masonry surfaces when they are not heavily soiled, thus needlessly introducing chemicals or moisture into his-toric materials.

Cleaning masonry surfaces without testing or without suffi-cient time for the testing results to be of value.

Building Exterior

Masonry: Brick, stone, terra cotta, concrete, adobe, stucco, and mortar

Building Exterior Masonry 23

Recommended

Cleaning masonry surfaces with the gentlest method possible, such as low pressure water and detergents, using natural bris-tle brushes.

Inspecting painted masonry surfaces to determine whether repainting is necessary.

Removing damaged or deteriorated paint only to the next sound layer using the gentlest method possible (e.g., hand-scraping) prior to repainting.

Applying compatible paint coating systems following proper surface preparation.

Repainting with colors that are historically appropriate to the building and district.

Evaluating the existing condition of the masonry to deter-mine whether more than protection and maintenance are required, that is, if repairs to masonry features will be neces-sary.

Repairing, stabilizing, and conserving fragile masonry by using well-tested consolidants, when appropriate. Repairs should be physically and visually compatible and identifiable upon close inspection for future research.

Not Recommended

Sandblasting brick or stone surfaces using dry or wet grit or other abrasives. These methods of cleaning permanently erode the surface of the material and accelerate deterioration.

Using a cleaning method that involves water or liquid chemi-cal solutions when there is any possibility of freezing temper-atures.

Cleaning with chemical products that will damage masonry, such as using acid on limestone or marble, or leaving chemi-cals on masonry surfaces.

Applying high pressure water cleaning methods that will damage historic masonry and the mortar joints.

Removing paint that is firmly adhering to, and thus protect-ing, masonry surfaces.

Using methods of removing paint which are destructive to masonry, such as sandblasting, application of caustic solu-tions, or high pressure waterblasting.

Failing to follow manufacturers’ product and application instructions when repainting masonry.

Using new paint colors that are inappropriate to the historic building and district.

Failing to undertake adequate measures to assure the protec-tion of masonry features.

Removing masonry that could be stabilized, repaired and conserved; or using untested consolidants and untrained per-sonnel, thus causing further damage to fragile materials.

24 Building Exterior Masonry

Recommended

Repairing masonry walls and other masonry features by repointing the mortar joints where there is evidence of deteri-oration such as disintegrating mortar, cracks in mortar joints, loose bricks, damp walls, or damaged plasterwork.

Removing deteriorated mortar by carefully hand-raking the joints to avoid damaging the masonry.

Duplicating old mortar in strength, composition, color, and texture.

Duplicating old mortar joints in width and in joint profile.

Adequate protection and maintenance of a historic building is an ongoing commitment. Here, two workers are priming and repainting exterior stone and wood trim. If surface treatments are neglected, more extensive repair and replacement will be required. Each loss further undermines a building’s historic integrity.

Not Recommended

Removing nondeteriorated mortar from sound joints, then repointing the entire building to achieve a uniform appearance.

Using electric saws and hammers rather than hand tools to remove deteriorated mortar from joints prior to repointing.

Repointing with mortar of high portland cement content (unless it is the content of the historic mortar). This can often create a bond that is stronger than the historic material and can cause damage as a result of the differing coefficient of expan-sion and the differing porosity of the material and the mortar.

Repointing with a synthetic caulking compound.

Using a “scrub” coating technique to repoint instead of tradi-tional repointing methods.

Changing the width or joint profile when repointing.

Building Exterior Masonry 25

Recommended

Repairing stucco by removing the damaged material and patching with new stucco that duplicates the old in strength, composition, color, and texture.

Using mud plaster as a surface coating over unfired, unstabi-lized adobe because the mud plaster will bond to the adobe.

Cutting damaged concrete back to remove the source of dete-rioration (often corrosion on metal reinforcement bars). The new patch must be applied carefully so it will bond satisfacto-rily with, and match, the historic concrete.

Repairing masonry features by patching, piecing-in, or other-wise reinforcing the masonry using recognized preservation methods. The new work should be unobtrusively dated to guide future research and treatment.

Applying new or non-historic surface treatments such as water-repellent coatings to masonry only after repointing and only if masonry repairs have failed to arrest water penetration problems.

Recommended

Limited Replacement in Kind

Replacing in kind extensively deteriorated or missing parts of masonry features when there are surviving prototypes such as terra-cotta brackets or stone balusters. The new work should match the old in material, design, color, and texture; and be unobtrusively dated to guide future research and treatment.

Not Recommended

Removing sound stucco; or repairing with new stucco that is stronger than the historic material or does not convey the same visual appearance.

Applying cement stucco to unfired, unstabilized adobe.

Because the cement stucco will not bond properly, moisture can become entrapped between materials, resulting in acceler-ated deterioration of the adobe.

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