Identify, Retain and Preserve
Identifying, retaining, and preserving structural
systems--and individual features of systems--that are
important in defining the overall historic character
of the building, such as post and beam systems, trusses,
summer beams, vigas, cast iron columns, above-grade
stone foundation walls, or loadbearing brick or stone
walls.
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This 20th century reinforced concrete tire
manufacturing building
features a large central interior
volume with side passages on three levels. Notable
elements include its generous space, splayed
tops to the columns that disperse the load from
the adjacent floors, and an attractive curved
hanging stair from an adjacent floor to the side
passage. The load-bearing structural elements
should remain exposed in any re-configuration for a new use
and the large volume should not be substantially
subdivided. Photo: William Manly, 1989. HAER Collection,
NPS.
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Removing, covering, or radically changing visible features
of structural systems which are important in defining
the overall historic character of the building so that,
as a result, the character is diminished.
Putting a new use into the building which could overload
the existing structural system; or installing equipment
or mechanical systems which could damage the structure.
Demolishing a loadbearing masonry wall that could be
augmented and retained, and replacing it with a new
wall (i.e., brick or stone), using the historic masonry
only as an exterior veneer.
Leaving known structural problems untreated such as
deflection of beams, cracking and bowing of walls, or
racking of structural members.
Utilizing treatments or products that accelerate the
deterioration of structural material such as introducing
urea-formaldehyde foam insulation into frame walls
Protect and Maintain
Protecting and maintaining the structural system
by cleaning the roof gutters and downspouts; replacing
roof flashing; keeping masonry, wood, and architectural
metals in a sound condition; and ensuring that structural
members are free from insect infestation.
Examining and evaluating the physical condition
of the structural system and its individual features
using non-destructive techniques such as X-ray photography.
Failing to provide proper building maintenance so that
deterioration of the structural system results. Causes
of deterioration include subsurface ground movement,
vegetation growing too close to foundation walls, improper
grading, fungal rot, and poor interior ventilation that
results in condensation.
Utilizing destructive probing techniques that will
damage or destroy structural material.
Repair
Repairing the structural system by augmenting or
upgrading individual parts or features. For example,
weakened structural members such as floor framing can
be paired with a new member, braced, or otherwise supplemented
and reinforced.
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Before interior rehabilitation began, structural stabilization of the historic masonry walls was undertaken through a series of exterior braces. Photo: NPS files.
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Upgrading the building structurally in a manner that
diminishes the historic character of the exterior, such
as installing strapping channels or removing a decorative
cornice; or damages interior features or spaces.
Replacing a structural member or other feature of the
structural system when it could be augmented and retained.
Replace
Replacing in kind--or with substitute material--those
portions or features of the structural system that are
either extensively deteriorated or are missing when
there are surviving prototypes such as cast iron columns,
roof rafters or trusses, or sections of loadbearing
walls. Substitute material should convey the same form,
design, and overall visual appearance as the historic
feature; and, at a minimum, be equal to its loadbearing
capabilities.
Installing a visible replacement feature that does not
convey the same visual appearance, e.g., replacing an
exposed wood summer beam with a steel beam.
Using substitute material that does not equal the loadbearing
capabilities of the historic material and design or
is otherwise physically or chemically incompatible.
The following work is
highlighted to indicate that it represents the
particularly complex technical or design aspects
of Rehabilitation projects and should only be
considered after the preservation concerns listed
above have been addressed.
Alterations/Additions for the New Use
Limiting any new excavations adjacent to historic
foundations to avoid undermining the structural
stability of the building or adjacent historic
buildings. Studies should be done to ascertain
potential damage to archeological resources.
Correcting structural deficiencies in preparation
for the new use in a manner that preserves the
structural system and individual character-defining
features.
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In the example shown here, a rehabilitation
project took into account--and respected--the
unique industrial structural character of
a mill building in its conversion to retail
shops. In fact, the exposed structure is
an attractive component of the new interior
design. If these visible posts had been
altered or hidden, the existing industrial
character would have been lost. Photos: NPS files.
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Designing and installing new mechanical or
electrical systems when required for the new use
which minimize the number of cutouts or holes
in structural members.
Adding a new floor when required for the new
use if such an alteration does not damage or destroy
the structural system or obscure, damage, or destroy
character-defining spaces, features, or finishes.
Creating an atrium or a light well to provide
natural light when required for the new use in
a manner that assures the preservation of the
structural system as well as character-defining
interior spaces, features, and finishes.
Carrying out excavations or regrading adjacent
to or within a historic building which could cause
the historic foundation to settle, shift, or fail;
could have a similar effect on adjacent historic
buildings; or could destroy significant archeological
resources.
Radically changing interior spaces or damaging
or destroying features or finishes that are character-defining
while trying to correct structural deficiencies
in preparation for the new use.
Installing new mechanical and electrical systems
or equipment in a manner which results in numerous
cuts, splices, or alterations to the structural
members.
Inserting a new floor when such a radical change
damages a structural system or obscures or destroys
interior spaces, features, or finishes.
Inserting new floors or furred-down ceilings
which cut across the glazed areas of windows so
that the exterior form and appearance of the windows
are radically changed.
Damaging the structural system or individual
features; or radically changing, damaging, or
destroying character-defining interior spaces,
features, or finishes in order to create an atrium
or a light well.
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