TE 51 - Guidelines for Rehabilitating Historic Buildings.pdf

The Secretary of the Interior's Standards for Rehabilitation &

11ustrated Guidelines for Rehabilitating Historic Buildings

~~ u.s. Department of the Interior National Park Service Cultural Resources

Heritage Preservation Services

The Secretary of the Interior's Standards for Historic Preservation Projects with Guidelines for Applying the Standards were written in 1976 by W. Brown Morton III and Gary L. Hume (the ten Standards for Rehabili tation and their guidelines have been the most-used component of this larger document which also contains standards and guidelines for acquisition, protection, stabilization, preservation, restoration, and reconstruc tion). The guidelines to the rehabilitation standards were revised and expanded in 1983 by Gary L. Hume and Kay D. Weeks and issued together with the 1976 standards as a separate book entitled The Secretary of the Interior's Standards for Rehabilitation with Guidelines for Applying the Standards. The 1976 Standards for Rehabilitation were revised in 1990 by Gary L. Hume, H. Ward Jandl,and Kay D. Weeks following a public commenting period.

The Secretary of the Interior's Standard's for Rehabilitation and Illustrated Guidelines for Rehabilitating Historic Buildings / W.

Brown Morton III ... ret al.l ; Anne E. Grimmer and Kay D. Weeks, project directors.

p. cm.

Includes bibliographical references.

1. Architecture-United States-Conservation and restoration

Standards. 2. Historic buildings-United States-Conservation and restoration-Standards. I. Morton, W. Brown. n. Grimmer, Anne E.. III. Weeks, Kay D. N. United States. National Park Service.

Preservation Assistance Division. V. Title: Illustrated guidelines for rehabilitating historic buildings.

NA106.S41991

720' .28'8021873-dc20 91-27060

For sale by the U.S. Government Printing Office

Superintendent of Documents. Mail Stop: SSOP. WHshinglOn. DC 20402-932R

ISBN 0-16-035979-1

CIP

The Secretary of the Interior's Standards for Rehabilitation &

Illustrated Guidelines for Rehabilitating Historic Buildings

W. BROWN MORTON III • GARY L.HUME · KAY D. WEEKS · H . WARD JANDL

ANNE E. GRIMMER AND KAY D. WEEKS

Project Directors u.s. Department of the Interior National Park Service Heritage Preservation Services

Washington, D.C.

Reprinted 1997

Contents Acknowledgements 111 Building Interior

Structural Systems 47 Foreword IV

Building Interior The Secretary of the Interior's Spaces, Features, and Finishes 53 Standards for Rehabilitation V

Building Interior Guidelines for Rehabilitating Mechanical Systems 61 Historic Buildings Vlll

Building Site 67 Building Exterior Masonry 1 Setting District or Neighborhood 75

Building Exterior Energy Conservation 83 Wood 9

New Additions Building Exterior to Historic Buildings 89 Architectural Metals 17

Accessibility Considerations 95 Building Exterior Roofs 23 Health and Safety

Considerations 99 Building Exterior Windows 29

Appendix Building Exterior Entrances and Porches 35 Technical Guidance Publications 105

Building Exterior Storefronts 41

Contents i

11 Photography Credits

Photo Credit for Book Cover

FrontlBack Covers: Residential rehabilitation, Seattle, Washington. © 1991. Mary Randlett.

Photo Credits for Chapter Heads

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 or 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.

Acknowledgements T he illustrated version of the Standards and Guidelines for Rehabilitation was developed by the Technical Preservation Services Branch, Preservation Assistance Division of the National Park Service.

Project Directors Anne E. Grimmer and Ka yD. Weeks wish to thank those profes sional staff members who assisted in the book's preparation by providing technical review of the text, conducting photo research, and taking photographs. They include Michael J. Auer, Charles E. Fisher, Thomas C. Jester, Lauren G. Meier, ASLA, and Sharon C. Park, AlA. Tim Buehner prepared several technical draw ings. Special thanks go to Jack E. Boucher and Catherine LaVoie of the Historic American Buildings Survey (HABS) who were especially helpful in conducting photographic research. Boucher's work appears throughout the book. Mary Randlett's photograph of ongoing rehabili tation work is featured on the cover.

All photographs and drawings included in this publication not individually credited have been selected from National Park Service Files.

c o ;3 :;3

Acknowledgements iii

HA BS Collection iv Foreword

Foreword A banner year, 1991 marks the 75th anniversary of the National Park Service as well as 25 years of preservation achievements resulting from passage of the National Historic Preservation Act of 1966. Publication of the illustrated Guide lines for Rehabilitating Historic Buildings fittingly coincides with the celebration of this important Act that created our Na tional Register programs and established a solid Federal/State partnership nation wide. Since 1966, over 800,000 properties have been placed in the National Register of Historic Places through the joint efforts of State Historic Preservation Offices, Federal agencies, Certified Local Govern ments, and the private sector. Over the past quarter century, historic preservation grants to the States for survey, planning and rehabilitation have amounted to nearly $600 million, an investment total ing close to $1.2 billion with the inclusion of matching non-Federal funds . Addition ally, the Preservation Tax Incentives, now in their 14th year, have contributed to the rehabilitation of nearly 22,000 historic properties, representing an investment of almost $15 billion in private funds .

The Secretary of the Interior's Standards are of particular relevance here because they have been used to determine the appropriateness of work treatments for every grant-in-aid and Tax Act project over a 25-year period. By emphasizing repair over replacement, and limited rather than wholesale change to accom modate new uses, the Standards and their accompanying Guidelines seek to ensure the preservation of those qualities for which each property was listed in the National Register.

Finally, this illustrated version of the Guidelines for Rehabilitating Historic Buildings has been designed to enhance overall understanding of basic preserva tion principles. Showing specific examples of appropriate treatments as well as the consequences of inappropriate treatments is just another aspect of a sustained effort to encourage the most respectful ap proaches possible in rehabilitating our nation's irreplaceable historic properties.

The Secretary of the Interior's Standards for Rehabilitation

Introduction to the Standards

The Secretary of the Interior is responsible for establishing standards for all programs under Departmental authority and for advising Federal agencies on the preserva tion of historic properties listed in or eligible for listing in the National Register of His toric Places. In partial fulfillment of this responsibility, the Secretary of the Interior's Standards for Historic Preservation Projects have been developed to guide work under taken on historic buildings; there are sepa rate standards for acquisition, protection, stabilization, preservation, rehabilitation, restoration, and reconstruction. The Stan dards for Rehabilitation (codified in 36 CFR

67) comprise that section of the overall preservation project standards and addresses the most prevalent treatment. "Rehabilita tion" is defined as "the process of returning a property to a state of utility, through repair or alteration, which makes possible an efficient contemporary use while preserv ing those portions and features of the prop erty which are significant to its historic, architectural, and cultural values."

Initially developed by the Secretary of the Interior to determine the appropriateness of proposed project work on registered properties within the Historic Preservation Fund grant-in-aid program, the Standards for Rehabilitation have been widely used over the years - particularly to determine if a rehabilitation qualifies as a Certified Rehabilitation for Federal purposes. In addition, the Standards have guided

Federal agencies in carrying out their his toric preservation responsibilities for properties in Federal ownership or control;

and State and local officials in reviewing

Introduction to the Standards v r ... I vi Standards for Rehabilitation both Federal and nonfederal rehabilitation proposals. They have also been adopted by historic district and planning commissions across the country.

The intent of the Standards is to assist the long-term preservation of a property's significance through the preservation of historic materials and features. The Stan dards pertain to historic buildings of all materials, construction types, sizes, and occupancy and encompass the exterior and interior of the buildings. They also encom pass related landscape features and the building'S site and environment, as well as attached, adjacent, or related new con struction. To be certified for Federal tax purposes, a rehabilitation project must be determined by the Secretary to be consis tent with the historic character of the structure(s), and where applicable, the district in which it is located.

As stated in the definition, the treatment "rehabilitation" assumes that at least some repair or alteration of the historic building will be needed in order to provide for an efficient contemporary use; however, these repairs and alterations must not damage or destroy materials, features or finishes that are importa'nt in defining the building's historic character. For example, certain treatments -if improperly applied-may cause or accelerate physical deterioration of the historic building. This can include using improper rep ointing or exterior masonry cleaning techniques, or introduc ing insulation that damages historic fabric.

In almost all of these situations, use of these materials and treatments will result in a project that does not meet the Stan dards. Similarly, exterior additions that duplicate the form, material, and detailing of the structure to the extent that they compromise the historic character of the structure will fail to meet the Standards.

The Secretary of the Interior's Standards for Rehabilitation

The Standards (Department of Interior regulations, 36 CFR 67) pertain to historic buildings of all materials, construction types, sizes, and occupancy and encompass the exterior and the interior, related land scape features and the building's site and environment as well as attached, adjacent, or related new construction. The Stan dards are to be applied to specific rehabili tation projects in a reasonable manner, taking into consideration economic and technical feasibility.

1. A property shall be used for its historic purpose or be placed in a new use that requires minimal change to the defining characteristics of the building and its site and environment.

2. The historic character of a property shall be retained and preserved. The removal of historic materials or alteration of features and spaces that characterize a property shall be avoided.

3. Each property shall be recognized as a physical record of its time, place, and use.

Changes that create a false sense of histori cal development, such as adding conjec tural features or architectural elements from other buildings, shall not be under taken.

4. Most properties change over time; those changes that have acquired historic signifi cance in their own right shall be retained and preserved.

5. Distinctive features, finishes, and con struction techniques or examples of crafts manship that characterize a property shall be preserved.

6. Deteriorated historic features shall be repaired rather than replaced. Where the severity of deterioration requires re placement of a distinctive feature, the new feature shall match the old in design, color, texture, and other visual qualities and, where possible, materials. Replace ment of missing features shall be sub stantiated by documentary, physical, or pictorial evidence.

7. Chemical or physical treatments, such as sandblasting, that cause damage to historic materials shall not be used. The surface cleaning of structures, if appropri ate, shall be undertaken using the gentlest means possible.

8. Significant archeological resources af fected by a project shall be protected and preserved. If such resources must be disturbed, mitigation measures shall be undertaken.

9. New additions, exterior alterations, or related new construction shall not destroy historic materials that characterize the property. The new work shall be differenti ated from the old and shall be compatible with the massing, size, scale, and architec tural features to protect the historic integ rity of the property and its environment.

10. New additions and adjacent or related new construction shall be undertaken in such a manner that if removed in the future, the essential form and integrity of the historic property and its environment would be unimpaired.

Standards for Rehabilitation vii

Drawing: Nicholas Satterlee

Guidelines for Rehabilitating Historic Buildings

Introduction to the Guidelines

The Guidelines for Rehabilitating His toric Buildings were initially developed in 1977 to help property owners, developers, and Federal managers apply the SecretaOry of the Interior's "Standards for Rehabilita tion" during the project planning stage by providing general design and technical recommendations. Unlike the Standards, the Guidelines are not codified as program requirements. Together with the "Stan dards for Rehabilitation," they provide a model process for owners, developers, and Federal agency managers to follow.

The Guidelines are intended to assist in applying the Standards to projects gener ally; consequently, they are not meant to give case-specific advice or address excep tions or rare instances. For example, they viii Introduction to the Guidelines cannot tell owners or developers which features of their own historic building are important in defining the historic charac ter and must be preserved-although examples are provided in each section or which features could be altered, if necessary, for the new use. This kind of careful case-by-case decision-making is best accomplished by seeking assistance from qualified historic preservation pro fessionals in the planning stage of the project. Such professionals include archi tects, architectural historians, historians, archeologists, and others who are skilled in the preservation, rehabilitation, and restoration of the historic properties.

The Guidelines pertain to historic build ings of all sizes, materials, occupancy, and construction types; and apply to interior and exterior work as well as new exterior additions. Those approaches, treatments, and techniques that are consistent with the Secretary of the Interior's "Standards for Rehabilitation" are listed in the "Recom mended" column on the left; those ap proaches, treatments, and techniques which could adversely affect a building's historic character are listed in the "Not Recommended" column on the right.

To provide clear and consistent guidance for owners, developers, and Federal agency managers to follow, the "Recom mended" courses of action in each section are listed in order of historic preservation concerns so that a rehabilitation project may be successfully planned and com pleted-one that, first, assures the preser vation of a building's important or "character-defining" architectural materi als and features and, second, makes pos sible an efficient contemporary use. Reha bilitation guidance in each section begins with protection and maintenance, that work which should be maximized in every project to enhance overall preservation goals. Next, where some deterioration is present, repair of the building's historic materials and features is recommended.

Finally, when deterioration is so extensive that repair is not possible, the most prob lematic area of work is considered:

replacement of historic materials and features with new materials.

To further guide the owner and developer in planning a successful rehabilitation pro ject, those complex design issues dealing with new use requirements such as alter ations and additions are highlighted at the end of each section to underscore the need for particular sensitivity in these areas.

Identify, Retain, and Preserve

The guidance that is basic to the treatment of all historic buildings-identifying, retaining, and preserving the form and detailing of those architectural materials and features that are important in defining the historic character-is always listed first in the "Recommended" column. The parallel "Not Recommended" column lists the types of actions that are most apt to cause the diminution or even loss of the building's historic character. It should be remembered, however, that such loss of character is just as often caused by the cumulative effect of a series of actions that would seem to be minor interventions.

Thus, the guidance in all of the "Not Recommended" columns must be viewed in that larger context, e.g., for the total impact on a historic building.

Protect and Maintain

After identifying those materials and features that are important and must be retained in the process of rehabilitation 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 mainte nance of historic material through treat-

Introduction to the Guidelines ix x Introduction to the Guidelines ments such as rust removal, caulking, limi ted paint removal, and re-application of protective coating; the cyclical cleaning of roof gutter systems; or installation of fenc ing, protective plywood, 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

Next, when the physical condition of character-defining materials and features warrants additional work repairing is recommended. Guidance for the repair of historic materials such as masomy, wood, and architectural metals again begins with the least degree of intervention possible such as patching, piecing-in, splicing, consolidating, or otherwise reinforcing or upgrading them according to recognized preservation methods. Repairing also includes the limited replacement in kind or with compatible substitute material of extensively deteriorated or missing parts of features when there are surviving proto types (for example, brackets, dentils, steps, plaster, or portions of slate or tile roofing).

Although using the same kind of material is always the preferred option, substitute material is acceptable if the form and design as well as the substitute material itself convey the visual appearance of the remaining parts of the feature and finish.

Replace

Following repair in the hierarchy, guid ance is provided for replacing an entire character-defining feature with new mate rial because the level of deterioration or damage of materials precludes repair (for example, an exterior cornice; an interior staircase; or a complete porch or store front). If the essential form and detailing are still evident so that the physical evi dence can be used to re-establish the feature as an integral part of the rehabilita tion project, then its replacement is appro priate. Like the guidance for repair, the preferred option is always replacement of the entire feature in kind, that is, with the

. I , same material. Because this approach may not always be technically or economically feasible, provisions are made to consider the use of a compatible substitute material.

It should be noted that, while the National Park Service guidelines recommend the replacement of an entire character-defining feature under certain well-defined circum stances, they never recommend removal and replacement with new material of a feature that-although damaged or deteriorated-could reasonably be re paired and thus preserved.

Design for Missing Historic Features

When an entire interior or exterior feature is missing (for example, an entrance, or cast iron facade; or a principal staircase), it no longer plays a role in physically defin ing the historic character of the building unless it can be accurately recovered in form and detailing through the process of carefully documenting the historical appearance. Where an important architec tural feature is missing, its recovery is always recommended in the guidelines as the first or preferred, course of action.

Thus, if adequate historical, pictorial, and physical documentation exists so that the feature may be accurately reproduced, and if it is desirable to re-establish the feature as part of the building's historical appear ance, then designing and constructing a new feature based on such information is appropriate. However, a second accept able option for the replacement feature is a new design that is compatible with the remaining character-defining features of the historic building. The new design should always take into account the size, scale, and material of the historic building itself and, most importantly, should be clearly differentiated so that a false histori cal appearance is not created.

Introduction to the Guidelines xi

Alterations/Additions to Historic Buildings

Some exterior and interior alterations to historic building are generally needed to assure its continued use, but it is most important that such alterations do not radically change, obscure, or destroy character-defining spaces, materials, features, or finishes. Alterations may include providing additional parking space on an existing historic building site; cutting new entrances or windows on secondary elevations; inserting an additional floor;

installing an entirely new mechanical system; or creating an atrium or light well.

Alteration may also include the selective removal of buildings or other features of the environment or building site that are intrusive and therefore detract from the overall historic character.

The construction of an exterior addition to a historic building may seem to be essential for the new use, but it is emphasized in the guidelines that such new additions should be avoided, if possible, and considered only after it is determined that those needs cannot be met by altering secondary, i.e., non character-defining interior spaces. If, after a thorough evaluation of interior solutions, an exterior addition is still judged to be the only viable alterative, it should be designed and constructed to be clearly differentiated from the historic xii Introduction to the Guidelines building and so that the character-defining features are not radically changed, obscured, damaged, or destroyed.

Additions to historic buildings are refer enced within specific sections of the guidelines such as Site, Roof, Structural Systems, etc., but are also considered in more detail in a separate section, New Additions to Historic Buildings.

Energy Conservation/Accessibility ConsiderationslHealth and Safety Code Considerations

These sections of the rehabilitation gui dance address work done to meet access ibility requirements and health and safety code requirements; or retrofitting mea sures to conserve energy. Although this work is quite often an important aspect of rehabilitation projects, it is usually not a part of the overall process of protecting or repairing character-defining features;

rather, such work is assessed for it poten tial negative impact on the building's historic character. For this reason, particu lar care must be taken not to radically change, obscure, damage, or destroy character-defining materials or features in the process of undertaking work to meet various code requirements.

Building Exterior

Masonry

BRICK

STONE

TERRA COTTA

CONCRETE

ADOBE

STUCCO

M ORTAR

Masonry

2 Building Exterior Masonry

The longevity and appearance of a ma sonry wall is dependent upon the size of the individual units and the mortar.

Stone is one of the more lasting of masonry building materials and has been used throughout the history of American build ing construction. The kinds of stone most commonly encountered on historic build ings in the U.S. include various types of sandstone, limestone, marble, granite, slate and fieldstone. Brick varied considerably in size and quality. Before 1870, brick clays were pressed into molds and were often unevenly fired. The quality of brick de pended on the type of clay available and the brick-making techniques; 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 widespread use of architectural terra cotta. Adobe, which consists of sun-dried earthen bricks, was one of the earliest permanent 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. After 1880, 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 damage by improper mainte nance or repair techniques and harsh or abrasive cleaning methods.

Graffiti applied with a felt tipped marker to polished granite is being removed with a misture of solvents. The slight ghost outline was successfully eliminated using the same solvent mixture in a clay poultice, followed by a thorough detergent and water rinse.

Recommended

Identify, retain, and preseroe 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.

Protect and maintain Protecting and maintaining masonry by provid ing proper drainage so that water does not stand on flat, horizontal surfaces 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 immedi ate and the long range effects are known to enable selection of the gentlest method possible.

Not Recommended

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

Replacing or rebuilding a major portion of exterior masonry walls that could be repaired so that, as a result, the building is no longer historic and is essentially new construction.

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

Removing paint from historically painted masonry.

Radically changing the type of paint or coating or its color.

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

Cleaning masonry surfaces when they are not heavily soiled to create a new appearance, thus needlessly introducing chemicals or moisture into historic materials.

Cleaning masonry surfaces without testing or without sufficient time for the testing results to be of value.

Building Exterior Masonry 3

Too hard and inflexible a mortar has caused this soft, 18th century brick to spall.

4 Building Exterior Masonry

Recommended

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

Inspecting painted masonry surfaces to deter mine whether repainting is necessary.

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

Applying compatible paint coating systems following proper surface preparation.

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

Not Recommended

When this brick wall was sand bLasted, a down spout (since removed) protected the originaL smooth surface of the center strip from damage.

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 chemical solutions when there is any possibility of freezing temperatures.

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

Using methods of removing paint which are destructive to ma sonry, such as sandblasting, application of caustic solutions, or high pressure waterblasting.

Failing to follow manufacturers' product and application instruc tions when repainting masonry.

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

Recommended

Evaluating the overall condition of the masonry to determine whether more than protection and maintenance are required, that is, if repairs to the masonry features will be necessary.

Repair Repairing masonry walls and other masonry features by rep ointing the mortar joints where there is evidence of deterioration such as disinte grating mortar, cracks in mortar joints, loose bricks, damp walls, or damaged plasterwork.

Not Recommended

Failing to undertake adequate measures to assure the protection of masonry features.

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

Composite patching with a cementitious mixture is being used to repair eroded areas of this sandstone facade.

Excessive moisture has damaged not only the stuc coed wall surface, but also the brick substrate.

6 Building Exterior Masonry

Recommended

Moisture from a faulty roof and drainage system has been trapped inside this limestone cornice by a waterproof coating, causing severe damage to the stone.

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.

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, unstabilized adobe because the mud plaster will bond to the adobe.

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--iiiiiiiiiiiiiil1 ui

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Not Recommended

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 expansion 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 rep ointing.

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 accelerated deteriora tion of the adobe.

A. Fkxible Mortar (lime)

8 . Inneldble Mortu (Cement)

Recommended

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

Repairing masonry features by patching, piec ing-in, or consolidating the masonry using recognized preservation methods. Repair may also include the limited replacement in kind -or with compatible substitute material-of those extensively deteriorated or missing parts of masonry features when there are surviving prototypes such as terra-cotta brackets or stone balusters.

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.

Hoi Cold Nomu.1 (Bricks exp~nd ) (Bricks contnlctl

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Mo rtar comprH.SeS Mortart'lvtH

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Not Recommended

Patching concrete without removing the source of deterioration.

Replacing an entire masonry feature such as a cornice or balus trade when repair of the masonry and limited replacement of deteriorated or missing parts are appropriate.

Using a substitute material for the replacement part that does not convey the visual appearance of the surviving parts of the ma sonry feature or that is physically or chemically incompatible.

Applying waterproof, water repellent, or non-historic coating such as stucco to masonry as a substitute for repointing and masonry repairs. Coatings are frequently unnecessary, expensive, and may change the appearance of historic masonry as well as accelerate its deterioration.

Flexible mortar expands and contracts with temperature changes. Bricks bonded by inflexible mortar tend to spall at the edges in hot weather and separate from the mortar when it is cold. Temperature fluctuations result in cracks which permit water to enter, causing additional deterioration.

Building Exterior Masonry 7

Replace Replacing in kind an entire masonry feature that is too deteriorated to repair-if the overall form and detailing are still evident-using the physi cal evidence as a model to reproduce the feature.

Examples can include large sections of a wall, a cornice, balustrade, column, or stairway. If using the same kind of material is not techni cally or economically feasible, then a compatible substitute material may be considered.

Not Recommended

Removing a masonry feature that is unrepairable and not replac ing it; or replacing it with a new feature that does not convey the same visual appearance.

Design for Missing Historic Features The following work is highlighted to indicate that it repre sents the particularly complex technical or design aspects of rehabilitation projects and should only be considered after the preservation concerns listed above have been addressed.

Recommended

Designing and installing a new masonry feature such as steps or a door pediment when the historic feature is completely missing. It may be an accurate restoration using historical, pictorial, and physical documentation; or be a new design that is compatible with the size, scale, material, and color of the historic building.

Not Recommended

Creating a false historical appearance because the replaced masonry feature is based on insufficient historical, pictorial, and physical documentation.

Introducing a new masonry feature that is incompatible in size, scale, material and color.

Coving-the hollowing out of an adobe wall just above grade-may be caused by standing rainwater, rainwater splash-up from the ground, or by salts deposited in the adobe by moisture evaporation. This adobe wall is being patched in the traditional manner with adobe mud.

Wood

CLAPBOARD

WEATHERBOARD

S HINGLES AND

OTHER WOODEN SIDING

AND D ECORATIVE ELEMENTS

Wood

10 Building Exterior Wood

B ecause it can be easily shaped by sawing, planing, carving, and gouging, wood is used for architec tural features such as clapboard, cornices, brackets, entablatures, shutters, columns and balustrades.

These wooden features, both functional and decorative, may be important in defining the historic character of the building and thus their retention, protection, and repair are important in rehabilita tion projects.

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

Due to lack of maintenance, the paint has peeled to bare wood.

In order to survive, this cornice will need to be scraped, sanded, and re painted together with other essen tial repairs.

Recommended

Identify, retain, and preserve Identifying, retaining, and preserving wood features that are important in defining the overall historic character of the building such as siding, cornices, brackets, window architraves, and doorway pediments; and their paints, finishes, and colors.

Protect and maintain Protecting and maintaining wood features by providing proper drainage so that water is not allowed to stand on flat, horizontal surfaces or accumulate in decorative features.

Applying chemical preservatives to wood features such as beam ends or outriggers that are exposed to decay hazards and are traditionally unpainted.

Not Recommended

Removing or radically changing wood features which are impor tant in defining the overall historic character of the building so that, as a result, the character is diminished.

Removing a major portion of the historic wood from a facade instead of repairing or replacing only the deteriorated wood, then reconstructing the facade with new material in order to achieve a uniform or "improved" appearance.

Radically changing the type of finish or its color or accent scheme so that the historic character of the exterior is diminished.

Stripping historically painted surfaces to bare wood, then applying clear finishes or stains in order to create a "natural look. "

Stripping paint or varnish to bare wood rather than repairing or reapplying a special finish, i.e., a grained finish to an exterior wood feature such as a front door.

Failing to identify, evaluate, and treat the causes of wood deteriora tion, including faulty flashing, leaking gutters, cracks and holes in siding, deteriorated caulking in joints and seams, plant material growing too close to wood surfaces, or insect or fungus infestation.

Using chemical preservatives such as creosote which can change the appearance of wood features unless they were used historically.

Building Exterior Wood 11

If a character defining feature is missing, it should be replaced with a matching feature.

This shop artisan used traditiollal tools to replicate a missing porch bracket; after the new bracket is painted, both original and duplicate will be installed on-site.

12 Building Exterior Wood

Recommended

Retaining coatings such as paint that help protect the wood from moisture and ultraviolet light.

Paint removal should be considered only where there is paint surface deterioration and as part of an overall maintenance program which involves repainting or applying other appropriate protec tive coatings.

Inspecting painted wood surfaces to determine whether repainting is necessary or if cleaning is all that is required.

Removing damaged or deteriorated paint to the next sound layer using the gentlest method possible (handscraping and handsanding), then repainting.

Not Recommended

Stripping paint or other coatings to reveal bare wood, thus exposing historically coated surfaces to the effects of accelerated weathering.

Removing paint that is firmly adhering to, and thus, protecting wood surfaces.

Replacing an entire wood feature such as a cornice or wall when repair of the wood and limited replacement of deteriorated or missing parts are appropriate.

Using substitute material for the replacement part that does not convey the visual appearance of the surviving parts of the wood feature or that is physically or chemically incompatible.

Using destructive paint removal methods such as a propane or butane torches, sandblasting or water blasting. These methods can irreversibly damage historic woodwork.

Deteriorated clapboards are being selectively replaced, thereby maximizing retention of the historic siding.

Recommended

Using with care electric hot-air guns on decora tive wood features and electric heat plates on flat wood surfaces when paint is so deteriorated that total removal is necessary prior to repainting.

Using chemical strippers primarily to supplement other methods such as handscraping, handsanding and the above-recommended thermal devices. Detachable wooden elements such as shutters, doors, and columns may with the proper safeguards- be chemically dip-stripped.

Applying compatible paint coating systems following proper surface preparation.

Not Recommended

Using thermal devices improperly so that the historic woodwork is scorched.

Failing to neutralize the wood thoroughly after using chemicals so that new paint does not adhere.

Allowing detachable wood features to soak too long in a caustic solution so that the wood grain is raised and the surface roughened.

Failing to follow manufacturers' product and application instruc tions when repainting exterior woodwork.

Building Exterior Wood 13

To replace deteriorated portions of the column, strips of new wood were milled to conform to the shape and appearance of the old column framework, glued in place, then back-primed and painted.

14 Building Exterior Wood

Recommended

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

Evaluating the overall condition of the wood to determine whether more than protection and maintenance are required, that is, if repairs to wood features will be necessary.

Repair Repairing wood features by patching, piecing-in, consolidating, or otherwise reinforcing the wood using recognized preservation methods. Repair may also include the limited replacement in kind-or with compatible substitute material of those extensively deteriorated or missing parts of features where there are surviving prototypes such as brackets, molding, or sections of siding.

Replace Replacing in kind an entire wood feature that is too deteriorated to repair-if the overall form and detailing are still evident-using the physical evidence as a model to reproduce th~ feature.

Examples of wood features include a cornice, entablature or balustrade. If using the same kind of material is not technically or economically feasible, then a compatible substitute material may be considered.

Not Recommended

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

Failing to undertake adequate measures to assure the protection of wood features.

Replacing an entire wood feature such as a cornice or wall when repair of the wood and limited replacement of deteriorated or missing parts are appropriate.

Using substitute material for the replacement part that does not convey the visual appearance of the surviving parts of the wood feature or that is physically or chemically incompatible.

Removing an entire wood feature that is unrepairable and not replacing it; or replacing it with a new feature that does not convey the same visual appearance.

Design for Missing Historic Features The following work is highlighted to indicate that it represents the particularly complex technical or design aspects of rehabili tation projects and should only be considered after the preser vation concerns listed above have been addressed.

Recommended

Designing and installing a new wood feature such as a cornice or doorway when the historic feature is completely missing. It may be an accurate restoration using historical, pictorial, and physical documentation; or be a new design that is compatible with the size, scale, material, and color of the historic building.

Not Recommended

Creating a false historical appearance because the replaced wood feature is based on insufficient historical, pictorial, and physical documentation.

Introducing a new wood feature that is incompatible in size, scale, material and color.

As protection from the extremes of weather, paint should be re-applied to exterior wood on a regular basis.

Building Exterior Wood 15

Architectural Metals

CAST IRON

STEEL

PRESSED TIN

COPPER

ALUMINUM

ZINC

Architectural Metals

Architectural metal features-such as cast iron facades, porches, and steps; sheet metal cornices, siding, 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 historic character of the building.

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 aluminum.

Historic metal building components were often created by highly skilled, local arti sans, and by the late 19th century, many of these components were prefabricated and readily available from catalogs in standard ized sizes and designs.

18 Building Exterior Architectural Metals li' g .g oj t: ..... == The decorative cast-iron storefront column was sandblasted in order to remove flaking paint and rust prior to repainting. Unlike soft metals such as copper and tin, which are damaged by abrasive cleaning, sandblasting is an appropriate method for cleaning cast iron, a very hard metal.

Recommended

Identify~ retain~ and preseroe Identifying, retaining, and preserving architec tural metal features such as columns, capitals, window hoods, or stairways that are important in defining the overall historic character of the building; and their finishes and colors. Identifica tion is also critical to differentiate between metals prior to work. Each metal has unique properties and thus requires different treatments .

Protect and maintain Protecting and maintaining architectural metals from corrosion by providing proper drainage so that water does not stand on flat, hori-zontal surfaces or accumulate in curved, decora tive features.

Cleaning architectural metals, when appropriate, to remove corrosion prior to repainting or apply ing other appropriate protective coatings.

Identifying the particular type of metal prior to any cleaning procedure and then testing to assure that the gentlest cleaning method possible is selected or determining that cleaning is inappro priate for the particular metal.

Not Recommended

Removing or radically changing architectural metal features which are important in defining the overall historic character of the building so that, as a result, the character is diminished.

Removing a major portion of the historic architectural metal from a facade instead of repairing or replacing only the deteriorated metal, then reconstructing the facade with new material in order to create a uniform, or "improved" appearance.

Radically changing the type of finish or its historic color or accent scheme.

Failing to identify, evaluate, and treat the causes of corrosion, such as moisture from leaking roofs or gutters.

Placing incompatible metals together without providing a reliable separation material. Such incompatibility can result in galvanic corrosion of the less noble metal, e.g., copper will corrode cast iron, steel, tin, and aluminum.

Exposing metals which were intended to be protected from the environment.

Applying paint or other coatings to metals such as copper, bronze, or stainless steel that were meant to be exposed.

Using cleaning methods which alter or damage the historic color, texture, and finish of the metal; or cleaning when it is inappropri ate for the metal.

Removing the patina of historic metal. The patina may be a protec tive coating on some metals, such as bronze or copper, as well as a significant historic finish.

Building Exterior Architectural Metals 19

Although these pressed metal storefronts have been well maintained over the years, gaps ill the seams between the metal sheets above the door and slight stains along the cornice line indicate a possible roof leak. The roof should be in vestigated and repaired before the moisture results ill rust and more severe metal deterioration.

Recommended

Cleaning soft metals such as lead, tin, copper, terneplate, and zinc with appropriate chemical methods because their finishes can be easily abraded by blasting methods.

Using the gentlest cleaning methods for cast iron, wrought iron, and steel-hard metals - in order to remove paint buildup and corrosion. If handscraping and wire brushing have proven ineffective, low pressure grit blasting may be used as long as it does not abrade or damage the…