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Buildings and Structures: Exteriors
Exteriors
A property's exterior envelope provides protection from the elements,
and to a large extent conveys its historic character. The age, style, and significance
of a building or structure can often be understood by analyzing exterior
designs, features, and materials. Exterior changes in taste, fashion, architectural
style, and use may also be evident. In any preservation project, it is critical
that the exterior be treated carefully. The following information describes
preservation treatments and approaches for the repair and maintenance
of the exteriors of historic buildings and structures.
Roofs
Roofs are more than simply the structure protecting the interior of a building
from the elements: they can be significant design features, notable for their
shape, height, color or pattern, configuration and materials.
Historic roofing materials are distinguishing elements of a building,
defining overall style, and reflecting the age and design of the property. As
with all historic materials, emphasis should be on retention and repair. Many
materials, such as slate or tile, if carefully maintained can last for many
years, and may need only careful attention and repair. However, since the roof
is constantly exposed to the elements, it may reach a point where partial or
major replacement is necessary. If this is the case, the historic materials
should be replaced to match the existing in color, texture, size, and other visual
qualities. Replacement in like material is always the preferred choice, but
if a substitute material is necessary or warranted, choosing the new to match
the historic appearance is critically important. The best course of action in maintaining a
roof is periodic inspection and repair. Gutter and flashing failure, plus lack of proper
maintenance, is often the culprit in a leaky roof. Owners should carefully examine gutters, leaders, valleys
and flashing before determining that wholesale roof replacement is necessary. Any repairs
at these areas should be made using materials and techniques meant to last long-term, not
simply a short-term "fix". Other materials, such as roofing compounds, do not
solve the real problem, are subject to early failure, and can be unsightly.
Masonry: Cleaning, Repointing and Repair
As with all historic materials, frequent evaluation, and careful maintenance of historic masonry
can solve minor problems before they become large expensive repairs.
Cleaning
In general, cleaning of historic masonry is not recommended, as it has the potential to cause
damage. Cleaning should be undertaken only when dirt or other material obscures significant
architectural features or is causing or has the potential to cause damage to masonry materials.
Cleaning should not remove the patina which is evidence of a building or structure's history and
age, and should never be performed for the sole purpose of achieving a "new" appearance.
When planning to clean an historic building or structure, the initial assessment should evaluate
the historic material, the reason for cleaning and the cleaning method. Cleaning methods should be
carefully selected to do the job without harming the historic material.
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Sugar Hill Historic District
Manhattan, New York County |
Acidic cleaners or highly alkaline cleaners can cause damage to historic materials and are
generally inappropriate. Only non-acidic neutral pH detergents should be used in conjunction with
non-metallic brushes or scrapers. Water pressure for cleaning should not exceed 150-200 psi., since
higher pressures can damage historic masonry units and mortar.
Abrasive methods such as grit blasting or "sandblasting" should never be used.
They are extremely damaging to historic materials in that they accelerate the deterioration of historic masonry
materials and can greatly change a building or structure's appearance.
If masonry surfaces were painted historically, they should remain painted. This
coating could have a specific protective function or play a part in the historic design and appearance.
If the covering is non-historic and deemed appropriate for removal, it should be removed as gently as
possible. Test patches should be performed prior to selecting a removal product or method, beginning with
the lowest recommended concentration of product and working upward to find the appropriate level; water
pressures should not exceed 150-200 psi.
Repointing
Repointing, the term used for repair of deteriorated mortar joints, is done by removing any old,
deteriorated mortar and replacing it with new. Repointing can be important to the continued sound
physical condition of a building and has the potential to affect the appearance of historic masonry.
The removal of deteriorated mortar should be undertaken only when absolutely necessary, usually where
mortar is eroded or crumbling. Most structures built until the early 20th century used lime mortar
with little or no cement binder. Removal of these low-strength mortars should be performed using
hand-held, non-power tools, since power tools such as masonry saws have the potential to damage
masonry units. Mortar made of hard Portland cement is much more difficult to remove from joints, and
use of hand-held chisels is likely to damage the masonry units. Here, carefully controlled pneumatic
chisels or small grinders may be appropriate, but these require extensive experience and quality
control to assure that the masonry units are not damaged. Complete repointing is seldom necessary,
nor is it a sound preservation treatment. New mortar should match the historic in strength,
composition, color, texture, aggregate distribution and all other qualities as determined by a
laboratory analysis. Prepackaged "masonry cements" generally contain large amounts of
Portland cement, and therefore produce a very strong mortar that can be damaging to softer historic
bricks and terra cotta. If mortar analysis is not undertaken to determine the composition of the
original mortar, the following soft, lime-rich mortar mix is appropriate for use on most historic
masonry: 1 part white Portland cement; 3 parts Type S hydrated lime; 6 parts sand with no
admixtures Because color additives can weaken masonry if used in large quantities, a color
match is best achieved using only appropriate colored aggregates (sand, brick dust, etc.)
Equally important to mortar content is the appearance of new mortar joints. New joints should
match the historic in width, tooling, texture and profile. Special character-defining joints such
as "ruled" or "grapevine" should be repaired or reproduced carefully.
Repair
Masonry materials may require repair as well as repointing and appropriate techniques will vary
according to the specific material. Because damaged brick units are difficult to repair, replacement
may be most appropriate and may involve using new or salvaged brick. If repair is not possible and
replacement is necessary, new units should match the existing in size, color, texture and all other
qualities. Historic stone materials that are damaged should be treated carefully. In keeping
with the preservation Standards, the best approach is repair. Replacement should only be considered
if the material is deteriorated beyond repair. Where cracked, spalled or exfoliated, limestone,
sandstone, marble, terra cotta, cast stone or concrete materials should be repaired to prevent
further damage. The type of stone, and type and extent of damage should be determined before the
repair method is chosen. The repair should be carefully executed to match the damaged material.
Information on appropriate specific treatments for historic masonry materials can be obtained from
the SHPO.
Cladding and Siding
Historic cladding materials are highly visible and significant features of a building's exterior.
Different materials such as clapboard, shingles, pressed metal, stucco and tile were used in various
historic periods, and in many cases relate specifically to a particular style. Therefore, preservation
and repair of historic cladding materials is important to maintain the character of historic
buildings. Periodic inspections should be made to assess the condition of the cladding, and any
necessary repairs undertaken immediately. This approach can preventy damage or deterioration from
becoming widespread, saving money in the long run.
Any work should be carefully planned to have the least physical impact on cladding
materials. Any cleaning should be undertaken using careful, non-abrasive techniques. High
pressure blasting, using either water or abrasives, can be very damaging to historic materials
and should not be used. If the cladding material requires painting or caulking, these treatments
will serve as a primary weathershield. As with all historic material, damaged sections should be
replaced in-kind to match the historic in all visual and physical qualities.
The installation of vinyl or metal siding materials over historic cladding, or the
replacement of historic materials with vinyl or metal, is not an appropriate preservation
treatment. Substitute materials may dramatically alter the historic appearance and character of
a building in many ways: the width of substitute siding often does not match historic clapboard
width, shadow reveals are reduced, and trim is frequently changed or removed at cornices,
corners, windows, and doors. Historic decorative shingles or vergeboards, as well as other
materials and patterns, may be completely obscured or destroyed. Moreover,
substitute siding has the potential to cause serious long-term damage to a building by trapping
moisture or by covering the early signs of deterioration that, left unchecked, can lead to major
repairs and structural problems.
Foremost among potential damage concerns is the accelerated deterioration of structural
elements from moisture trapped unnoticed behind substitute materials. The moisture can drastically decrease
the efficiency of insulation. Related interior consequences include peeling paint or wallpaper and
cracked wall surfaces. Substitute materials are also problematic because repair will almost always
be noticeable--the colors fade over time and products may be changed or discontinued.
When properly maintained, historic cladding materials such as clapboard and shingles
are durable and serviceable; their existence on thousands of historic buildings and structures after decades of
service is proof that they are economic and long-term alternatives. Their repair is strongly
recommended.
Windows
Historic windows are among the most important features in defining a building or structure's
character, and proper treatment is extremely important. Historic windows should be periodically
inspected and properly maintained; frequent maintenance now can prevent headaches later. A painted
wood window relies on its paint for weather protection. Without paint, the extremes of heat, cold,
sunlight and moisture can quickly act on the exterior frame and sash, damaging the wood. Therefore
the routine inspection of the windows, followed by appropriate scraping, priming and painting should
be foremost in any maintenance plan.
If inspection of a window reveals repairable damage or deterioration, existing window sash
and frames should be retained and repaired, rather than replaced, whenever possible. Unlike
modern metal replacement windows, historic wood units were constructed so that damaged portions
could be repaired or replaced one part at a time. A damaged window component should be replaced
with material and construction matching the original; this approach results in cost savings for
the building owner.
Replacement of an entire window unit is appropriate only when it is deteriorated beyond repair.
The new window should match the original in material, finish, configuration, setback, profiles and
all other visual, physical and reflective qualities.
Historic metal sash windows, both casement and double-hung, are also important features that
should be retained and repaired. In buildings such as historic industrial or institutional complexes,
rows of large historic metal windows contribute to the property's exterior character and should be
repaired and retained. Steel and other metal windows have their own sets of problems and treatments,
but specific guidance is available through the SHPO.
Storefronts
Storefronts are highly visible features of historic commercial buildings and every effort should
be made to preserve and rehabilitate intact historical examples. Since facades were often changed to
suit stylistic changes, the current storefront may not be original to the building. However, many of
these "later" storefronts are significant in their own right--for example, Art Deco
features on a 19th century building. These important features are a record of changes made over time
within a community or neighborhood and may reflect broad trends in economic development, architecture
and settlement patterns.
General periodic inspection and maintenance is key to the long life of any storefront system.
Appropriate painting, caulking and repair should be undertaken as soon as any problems are
identified. A prompt response to minor problems can prevent major repairs later.
Historic storefront installations should be retained, even where no commercial use is proposed
in the re-use. Where a storefront is missing, restoration of the original condition is appropriate
provided it is based on conclusive physical or documentary evidence (not conjecture). If both the
storefront and the basis for restoration are missing, then the use of simple, generic and compatible
storefront features is appropriate. These features typically include simple framing and panels,
large glass areas and transom units, cornices, signboards and simple doors. Appropriate materials,
configurations and proportions will vary depending upon the style and significant features of the
building and any associated district.
New Construction and Related Demolition
New construction and related demolition at historic properties can be a serious preservation issue. Just
as historic resources vary, new construction should be tailored to the historic property. The SHPO can
provide assistance in new construction projects and has developed general guidelines that can be useful
during project planning. The primary objective is to determine if the property can accept the addition
of a new feature without impact to the historical design, features and materials of the
property.
A side or rear secondary elevation is usually the best location for additions to historic buildings. Any new
addition should not impact or change the general perception of the building's historic design. As part
of this approach, the addition should be designed to be compatible with the architectural character of the
historic building, incorporating materials that complement the historic. The real challenge, however,
comes in insuring that the new addition is compatible without being a carbon copy of the historic building.
While it should be clear to the casual observer that the addition is new and not historic, the design and
materials of the new construction must respect and reflect the historic building.
New additions to other property types should be given the same consideration. New
construction within an historic landscape should be placed in the least prominent and least significant
spaces. New additions - such as new vegetation, circulation, or furnishings and objects - should be
compatible with the physical and visual characteristics of the specific landscape; cookie-cutter solutions
from one location may not be appropriate in others.
Rooftop Additions
New rooftop construction is an extremely sensitive issue in a preservation project. Rooftop additions
are inappropriate at most historic properties because they can seriously change the height, profile, and
overall exterior character of a building, as well as affect the overall character of an historic landscape
or historic district. Any proposed construction will be reviewed for its overall visibility from all
viewpoints. In general, a successful rooftop addition is small in scale and footprint, held away from the
building's perimeter, and visible from a limited number of vantage points. The exceptions are elevator
overruns and areas of fire refuge; such elements involve minor changes and are therefore usually
acceptable.
Parking Additions
Work associated with providing parking at an historic property can be of great concern. Contemporary
parking facilities--whether surface lots or garages--can greatly alter a property's historic character
and, in most cases, involves the loss of historic features and/or materials. Any proposed parking facility,
including its entries/exits, approaches and support features (lighting, security elements), will be
reviewed carefully. Emphasis will be on assessing the effect on important spaces, views, topography,
vegetation and buildings/structures.
Demolition
Demolition should be kept to an absolute minimum in any preservation project, and limited to secondary
areas or areas of extreme deterioration. Any demolition should be carefully planned to minimize impacts on
historic features and materials, as well as building floorplans or site plans.
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