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Historic Preservation - Technical Procedures

Spectitle:

Preservation Briefs: 14 New Exterior Additions To Historic Buildings: Preservation Concerns

Procedure code:

0110005S

Source:

Preservation Briefs 14, National Park Service, Pad

Division:

General Requirements

Section:

Special Project Procedures

Last Modified:

09/10/2012

Details:

Preservation Briefs: 14 New Exterior Additions To Historic Buildings: Preservation Concerns



PRESERVATION BRIEFS:  14

NEW EXTERIOR ADDITIONS TO HISTORIC BUILDINGS:  PRESERVATION
CONCERNS

 

The link immediately below connects to the latest version of National Park Service Preservation Brief 14:

 

http://www.nps.gov/history/hps/tps/briefs/brief14.pdf


Kay D. Weeks

This standard includes the bulk of information contained in the
original Preservation Brief developed by the National Park Service.
To obtain a complete copy of this brief, including figures and
illustrations, please contact:  

              Superintendent of Documents
              P.O. Box 371954
              Pittsburgh, PA  15250-7954

              GPO #024-005-01026-2
              Availabel ONLY in package sets
              Briefs 1-14 - $13.00

Please call the Publication Order Information Desk at 202/783-3238
or FAX 202/512-2250 to verify price and availability.  


BECAUSE A NEW EXTERIOR ADDITION TO AN 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.


***INTRODUCTION***

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 an 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, 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 an
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 an 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 an 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.


***PRESERVING SIGNIFICANT HISTORIC MATERIALS AND FEATURES***

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

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
an 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 an 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.


***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.  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 an 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 mock-up 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 building.


***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 . . . "

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 an historic
resource:

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

    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 additional
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 building's 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.

                         END OF SECTION
 


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