14

New Exterior Additions 

to Historic Buildings 

Preservation Concerns 

Kay D. Weeks

»Preserving Significant Historic Materials and Features

»Preserving the Historic Character 

»Protecting the Historical Significance 

»Conclusion

»Additional Reading

Because a new exterior addition to a historic building can damage or destroy significant materials and can 

change the building's character, an addition should be considered only after it has been determined that the 

new use cannot be met by altering nonsignificant, or secondary, interior spaces. If the new use cannot be met 

in this way, then an attached addition may be an acceptable alternative if carefully planned. A new addition 

should be constructed in a manner that preserves significant materials and features and preserves the historic 

character. Finally, an addition should be differentiated from the historic building so that the new work is not 

confused with what is genuinely part of the past.

Change is as inevitable in buildings and neighborhoods as it is in individuals and families. Never 

static, buildings and neighborhoods grow, diminish, and continue to evolve as each era's technological 

advances bring conveniences such as heating, street paving, electricity, and air conditioning; as the effects of 

violent weather, uncontrolled fire, or slow unchecked deterioration destroy vulnerable material, as businesses 

expand, change hands, become obsolete, as building codes are established to enhance life safety and health; 

or as additional family living space is alternately needed and abandoned. 

Preservationists generally agree that the history of a building, together with its site 

and setting, includes not only the period of original construction but frequently later 

alterations and additions. While each change to a building or neighborhood is 

undeniably part of its history--much like events in human life--not every change is 

equally important. For example, when a later, clearly nonsignificant addition is 

removed to reveal the original form, materials, and craftsmanship, there is little 

complaint about a loss to history. 

When the subject of new exterior additions is introduced, however, areas of 

agreement usually tend to diminish. This is understandable because the subject 

raises some serious questions. Can a historic building be enlarged for a new use 

without destroying what is historically significant? And just what is significant about 

each particular historic building that should be preserved? Finally, what new 

construction is appropriate to the old building? 

The vast amount of literature on the subject of change to America's built 

environment reflects widespread interest as well as divergence of opinion. New 

additions have been discussed by historians within a social and political, 

framework; by architectural historians in terms of construction technology and 

style; and by urban planners as successful or unsuccessful contextual design. 

Within the historic preservation programs of the National Park Service, however, 

A NOTE TO OUR USERS: The web versions of the Preservation Briefs differ somewhat from the printed versions. Many illustrations are new, 

captions are simplified, illustrations are typically in color rather than black and white, and some complex charts have been omitted. 

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the focus has been and will continue to be the protection of those resources 

identified as worthy of listing in the National Register of Historic Places. 

National Register Listing-- 

Acknowledging Change While Protecting Historical Significance 

Entire districts or neighborhoods may be listed in the National Register of Historic Places for their significance 

to a certain period of American history (e.g., activities in a commercial district between 1870 and 1910). This 

"framing" of historic districts has led to a concern that listing in the National Register may discourage any 

physical change beyond a certain historical period--particularly in the form of attached exterior additions. This 

is not the case. National Register listing does not mean that an entire building or district is frozen in time and 

that no change can be made without compromising the historical significance. It also does not mean that each 

portion of a historic building is equally significant and must be retained intact and without change. Admittedly, 

whether an attached new addition is small or large, there will always be some loss of material and some 

change in the form of the historic building. There will also generally be some change in the relationship 

between the buildings and its site, neighborhood or district. Some change is thus anticipated within each 

rehabilitation of a building for a contemporary use. 

Scope of National Park Service Interest in New Exterior Additions 

The National Park Service interest in new additions is simply this--a new addition to a historic building has the 

potential to damage and destroy significant historic material and features and to change its historic character. 

A new addition also has the potential to change how one perceives what is genuinely historic and thus to 

diminish those qualities that make the building eligible for listing in the National Register of Historic Places. 

Once these basic preservation issues have been addressed, all other aspects of designing and constructing a 

new addition to extend the useful life of the historic building rest with the creative skills of the architect. 

The intent of this Brief, then, is to provide guidance to owners and developers planning additions to their 

historic buildings. A project involving a new addition to a historic building is considered acceptable within the 

framework of the National Park Service's standards if it: 

1. Preserves significant historic materials and features; and 

2. Preserves the historic character; and 

3. Protects the historical significance by making a visual distinction between old and new. 

Paralleling these key points, the Brief is organized into three sections. Case study examples are provided to 

point out acceptable and unacceptable preservation approaches where new use requirements were met 

through construction of an exterior addition. These examples are included to suggest ways that change to 

historic buildings can be sensitively accomplished, not to provide in-depth project analyses, endorse or critique

particular architectural design, or offer cost and construction data. 

1. Preserving Significant Historic Materials and Features 

Connecting a new exterior addition always involves some degree of material loss to an external wall of a 

historic building and, although this is to be expected, it can be minimized. On the other hand, damage or 

destruction of significant materials and craftsmanship such as pressed brick, decorative marble, cast stone, 

terra-cotta, or architectural metal should be avoided, when possible. 

Generally speaking, preservation of historic buildings is enhanced by avoiding all but minor changes to primary

or "public" elevations. Historically, features that distinguish one building or a row of buildings and can be seen 

from the streets or sidewalks are most likely to be the significant ones. This can include window patterns, 

window hoods, or shutters; porticoes, entrances, and doorways; roof shapes, cornices, and decorative 

moldings; or commercial storefronts with their special detailing, signs, and glazing. Beyond a single building, 

entire blocks of urban or residential structures are often closely related architecturally by their materials, 

detailing, form, and alignment. Because significant materials and features should be preserved, not damaged 

or hidden, the first place to consider constructing a new addition is where such material loss will be minimized. 

This will frequently be on a secondary side or rear elevation. For both economic and social reasons, secondary 

elevations were often constructed of "common" material and were less architecturally ornate or detailed. 

The historic character of this 

commercial building has 

been radically changed by a 

replicative four-story 

addition. This approach does 

not meet the Standards for 

Rehabilitation. Photo: NPS 

files.

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In constructing the new addition, one way to minimize 

overall material loss is simply to reduce the size of the new 

addition in relationship to the historic building. If a new 

addition will abut the historic building along one elevation or 

wrap around a side and rear elevation, the integration of 

historic and new interiors may result in a high degree of 

loss--exterior walls as well as significant interior spaces and 

features. Another way to minimize loss is to limit the size 

and number of openings between old and new. 

A particularly 

successful method 

to reduce damage is 

to link the new 

addition to the 

historic block by 

means of a hyphen 

or connector. In this way, only the connecting passageway penetrates 

a historic side wall; the new addition can be visually and functionally 

related while historic materials remain essentially intact and historic 

exteriors remain uncovered. 

Although a general recommendation is to construct a new addition on 

a secondary elevation, there are several exceptions. First, there may 

simply be no secondary elevation--some important freestanding 

buildings have significant materials and features on all sides, making 

any above-ground addition too destructive to be considered. Second, a 

structure or group of structures together with their setting (for 

example, in a National Historic Park) may be of such significance in 

American history that any new addition would not only damage 

materials and alter the buildings' relationship to each other and the 

setting, but seriously diminish the public's ability to appreciate a 

historic event or place. Finally, there are other cases where an existing 

side or rear elevation was historically intended to be highly visible, is 

of special cultural importance to the neighborhood, or possesses 

associative historical value. Then, too, a secondary elevation should be treated as if it were a primary elevation

and a new addition should be avoided. 

2. Preserving the Historic Character 

The second, equally important, consideration is whether or not 

the new addition will preserve the resource's historic character.

The historic character of each building may differ, but a 

methodology of establishing it remains the same. Knowing the 

uses and functions a building has served over time will assist 

in making what is essentially a physical evaluation. But while 

written and pictorial documentation can provide a framework 

for establishing the building's history, the historic character, to 

a large extent, is embodied in the physical aspects of the 

historic building itself--its shape, its materials, its features, its 

craftsmanship, its window arrangements, its colors, its setting, 

and its interiors. It is only after the historic character has been 

correctly identified that reasonable decisions about the extent-

-or limitations--of change can be made. 

To meet National Park Service preservation standards, a new 

addition must be "compatible with the size, scale, color, 

material, and character" of the building to which it is attached 

or its particular neighborhood or district. A new addition will 

always change the size or actual bulk of the historic building. 

But an addition that bears no relationship to the proportions 

and massing of the historic building--in other words, one that 

overpowers the historic form and changes the scale will usually compromise the historic character as well. 

Two historic commercial buildings were successfully 

joined as part of a larger rehabilitation project. The 

glass connector detail is shown below. Photo: Martha L. 

Werenfels, AIA.

This small glass connector between two 

historic buildings is appropriately set back. 

This approach meets the Standards for 

Rehabilitation. Photo: Martha L. Werenfels, 

AIA.

This new stair tower addition on the rear elevation 

of a historic townhouse is compatible in size, scale, 

and materials. This approach meets the Standards 

for Rehabilitation. Photo: NPS files.

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The appropriate size for a new addition varies from building to 

building; it could never be stated in a tidy square or cubic 

footage ratio, but the historic building's existing proportions, site,

and setting can help set some general parameters for 

enlargement. To some extent, there is a predictable relationship 

between the size of the historic resource and the degree of 

change a new addition will impose. 

For example, in the case of relatively low buildings (small-scale 

residential or commercial structures) it is difficult, if not 

impossible, to minimize the impact of adding an entire new floor 

even if the new addition is set back from the plane of the facade. 

Alteration of the historic proportions and profile will likely change 

the building's character. On the other hand, a rooftop addition to 

an eight story building in a historic district of other tall buildings 

might not affect the historic character simply because the new 

work would not be visible from major streets. A number of 

methods have been used to help predict the effect of a proposed 

rooftop addition on the historic building and district, including 

pedestrian sight lines, three-dimensional schematics and 

computer-assisted design (CAD). Sometimes a rough full-size 

mock up of a section or bay of the proposed addition can be 

constructed using temporary material; the mockup can then be 

photographed and evaluated from critical vantage points. 

In the case of freestanding residential structures, the 

preservation considerations are generally twofold. 

First, a large addition built out on a highly visible 

elevation can radically alter the historic form or 

obscure features such as a decorative cornice or 

window ornamentation. Second, an addition that fills 

in a planned void on a highly visible elevation (such as 

a "U" shaped plan or feature such as a porch) may 

also alter the historic form and, as a result, change 

the historic character. 

Some historic structures such as government 

buildings, metropolitan museums, or libraries may be 

so massive in size that a large-scale addition may not 

compromise the historic character. Yet similar 

expansion of smaller buildings would be dramatically 

out of scale. In summary, where any new addition is 

proposed, correctly assessing the relationship 

between actual size and relative scale will be a key to 

preserving the character of the historic building. 

Constructing the new addition on a secondary side or 

rear elevation--in addition to material preservation--will

also address preservation of the historic character. 

Primarily, such placement will help to preserve the 

building's historic form and relationship to its site and 

setting. Historic landscape features, including 

distinctive grade variations, need to be respected; and 

any new landscape features such as plants and trees 

kept at a scale and density that would not interfere 

with appreciation of the historic resource itself. 

In highly developed urban areas, locating a new 

addition on a less visible side or rear elevation may be 

impossible simply because there is no available space. 

In this instance, there may be alternative ways to help 

preserve the historic character. If a new addition is 

being connected to the adjacent historic building on a 

primary elevation, the addition may be set back from 

the front wall plane so the outer edges defining the 

historic form are still apparent. In still other cases, some variation in material, detailing, and color may provide

the degree of differentiation necessary to avoid changing the essential proportions and character of the historic

This new stairtower addition on a historic 

university building has been constructed on a 

highly visible side elevation. Together with its 

contrasting color and size, it obscures the historic 

form and roofline. This approach does not meet 

the Standards for Rehabilitation. Photo: Martha L. 

Werenfels, AIA.

A sizeable addition was placed on a non-significant rear 

elevation of a late-19th century Greek Revival house that was 

rehabilitated for use as a bank with a drive-up component. The 

old building and new addition were sensitively joined by a small 

connecting hyphen. This approach meets the Standards for 

Rehabilitation. Photo: NPS files.

A contemporary new addition (above left) was designed to fit 

into a nonsignificant U-shaped area on a rear elevation of a 

historic library building. Note the new addition is lower than 

the historic building and clearly differentiated in appearance. 

This approach meets the Standards for Rehabilitation. Photo: 

NPS files.

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building. 

3. Protecting the Historical Significance 

Making a Visual Distinction Between Old and New 

The following statement of approach could be applied equally to the preservation of districts, sites, buildings, 

structures, and objects of National Register significance: "A conservator works within a conservation ethic so 

that the integrity of the object as an historic entity is maintained. The concern is not just with the original state

of the object, but the way in which it has been changed and used over the centuries. Where a new intervention

must be made to save the object, either to stabilize it or to consolidate it, it is generally accepted that those 

interventions must be clear, obvious, and reversible. It is this same attitude to change that is relevant to 

conservation policies and attitudes to historic towns..." (1) 

Rather than establishing a clear and obvious difference 

between old and new, it might seem more in keeping with

the historic character simply to repeat the historic form, 

material, features, and detailing in a new addition. But 

when the new work is indistinguishable from the old in 

appearance, then the "real" National Register property 

may no longer be perceived and appreciated by the 

public. 

Thus, the third consideration in planning a new addition is 

to be sure that it will protect those visual qualities that 

made the building eligible for listing in the National 

Register of Historic Places. 

A question often asked is what if the historic character is 

not compromised by an addition that appears to have been built in the same period? A small porch or a wing 

that copied the historic materials and detailing placed on a rear elevation might not alter the public perception 

of the historic form and massing. Therefore, it is conceivable that a modest addition could be replicative 

without changing the resource's historic character; generally, however, this approach is not recommended 

because using the same wall plane, roof line, cornice height, materials, siding lap, and window type in an 

addition can easily make the new work appear to be part of the historic building. If this happens on a visible 

elevation, it becomes unclear as to which features are historic and which are new, thus confusing the 

authenticity of the historic resource itself. 

The National Park Service policy on new additions, adopted in 1967, is an outgrowth and continuation of a 

general philosophical approach to change first expressed by John Ruskin in England in the 1850s, formalized 

by William Morris in the founding of the Society for the Protection of Ancient Buildings in 1877, expanded by 

the Society in 1924 and, finally, reiterated in the 1964 Venice Charter--a document that continues to be 

followed by 64 national committees of the International Council on Monuments and Sites (ICOMOS). The 1967 

Administrative Policies for Historical Areas of the National Park System thus states, "...a modern addition 

should be readily distinguishable from the older work; however, the new work should be harmonious with the 

old in scale, proportion, materials, and color. Such additions should be as inconspicuous as possible from the 

public view." Similarly, the Secretary of the Interior's 1977 "Standards for Rehabilitation" call for the new work

to be "compatible with the size, scale, color, material, and character of the property, neighborhood, or 

environment." 

Conclusion 

A major goal of our technical assistance program is a heightened awareness of significant materials and the 

historic character prior to construction of a new exterior addition so that essential change may be effected 

within a responsible preservation context. In summary, then, these are the three important preservation 

questions to ask when planning a new exterior addition to a historic resource: 

1. Does the proposed addition preserve significant historic materials and features? 

This highly visible new rooftop addition appears to be part 

of the historic building because of its replicative design 

and historicized detailing, such as the arched windows. 

This approach does not meet the Standards for 

Rehabilitation. Photo: NPS files.

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2. Does the proposed addition preserve the historic character? 

3. Does the proposed addition protect the historical significance by making a visual distinction 

between old and new? 

If the answer is YES to all three questions, then the new addition will protect significant historic materials and 

the historic character and, in doing so, will have satisfactorily addressed those concerns generally held to be 

fundamental to historic preservation. 

New Exterior Additions to Historic Buildings 

Preserve Significant Historic Materials and Features. 

Avoid constructing an addition on a primary or other character- defining elevation to ensure preservation of 

significant materials and features. 

Minimize loss of historic material comprising external walls and internal partitions and floor plans. 

Preserve the Historic Character 

Make the size, scale, massing, and proportions of the new addition compatible with the historic building to 

ensure that the historic form is not expanded or changed to an unacceptable degree. 

Place the new addition on an inconspicuous side or rear elevation so that the new work does not result in a 

radical change to the form and character of the historic building. 

Consider setting an infill addition or connector back from the historic buildings wall plane so that the form of 

the historic building--or buildings--can be distinguished from the new work. 

Set an additional story well back from the roof edge to ensure that the historic building's proportions and 

profile are not radically changed. 

Protect the Historical Significance--Make a Visual Distinction Between Old and New 

Plan the new addition in a manner that provides some differentiation in material, color, and detailing so that 

the new work does not appear to be part of the historic building. The character of the historic resource should 

be identifiable after the addition is constructed. 

Additional Reading 

Architecture: The AIA Journal, "Old and New," November, 1983. 

Brolin, Brent C. Architecture in Context: Fitting New Buildings with Old. New York: Van Nostrand Reinhold, 

1980. 

Good Neighbors: Building Next to History. State Historical Society of Colorado, 1980. 

International Council on Monuments and Sites (ICOMOS). International Charter for the Conservation and 

Restoration of Monuments and Sites (Venice Charter), 1966. 

National Trust for Historic Preservation. Old and New Architecture: Design Relationship. Washington, D.C.: 

Preservation Press. 1980. 

Rehab Right: How to Rehabilitate Your Oakland House Without Sacrificing Architectural Assets. City of Oakland 

Planning Department. Oakland, California, 1978. 

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Ruskin, John. The Seven Lamps of Architecture. London: George Allen and Unwin, Ltd., 1925. 

Schmertz, Mildred F., and Architectural Record Editors. New Life for Old Buildings. New York: Architectural 

Record Books, McGraw-Hill, 1980. 

The Secretary of the Interior's Standards for Rehabilitation and Guidelines for Rehabilitating Historic Buildings. 

Washington, D.C.: Preservation Assistance Division. National Park Service, U.S. Department of the Interior, 

rev. 1983. 

(1) Note: Roy Worskett, RIBA, MRTIP, "Improvement of Urban Design in Europe and the United States: New 

Buildings in Old Settings." Background Report (prepared July, 1984) for Seminar at Strasbourg, France, 

October, 1984. 

Acknowledgements 

First special thanks go to Ernest A. Connally, Gary L. Hume, and W. Brown Morton, III for their efforts in establishing and refining our preservation 

and rehabilitation standards over the past 20 years. ("The Secretary of the Interior's for Historic Preservation Projects (now"The Secretary of the 

Interior's Standards for the Treatment of Historic Properties (Rev. 1995)" constitute the policy framework of this, and every technical publication 

developed in the Preservation Assistance Division.) H. Ward Jandl, Chief, Technical Preservation Services Branch, is credited with overall supervision

of the project. Next appreciation is extended to the Branch professional staff, the NPS cultural programs regional offices, the Park Historic 

Architecture Division, and the National Conference of State Historic Preservation Officers for their thoughtful comments. Finally, the following 

specialists in the field are thanked for their time in reviewing and commenting on the manuscript: Bruce Judd, AIA, Nore V. Winter, John Cullinane, 

AIA, Ellen Beasley, Vicki Jo Sandstead, Judith Kitchen, Andrea Nadel, Martha L. Werenfels, Diane Pierce, Colden Florance, FAIA, and H. Grant 

Dehart, AIA. The photograph of Chicago's Newberry Library with the Harry Weese and Associates' 1981 addition was graciously lent to us by David 

F. Dibner, FAIA, and Amy Dibner-Dunlap, co-authors of Buildings Additions Design, McGraw-Hill, 1985. 

Washington, D.C. September, 1986.

Home page logo: Approriate new stair tower addition. Photo: NPS files. 

This publication has been prepared pursuant to the National Historic Preservation Act of 1966, as amended, 

which directs the Secretary of the Interior to develop and make available information concerning historic 

properties. Technical Preservation Services (TPS), Heritage Preservation Services Division, National Park

Service prepares standards, guidelines, and other educational materials on responsible historic preservation 

treatments for a broad public.

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