Identify, Retain and Preserve
Identifying, retaining, and preserving structural
systems from the restoration period--and individual
features of systems--such as post and beam systems,
trusses, summer beams, vigas, cast iron columns, above-grade
stone foundation walls, or loadbearing brick or stone
Exterior stone walls comprise the structural system of this small building that is part of an 1875 farmstead located in Dickinson County,
Kansas. Photos: David Johnson, HABS Collection,
Altering visible features of structural systems from
the restoration period.
Failing to properly document structural systems from
the restoration period which may result in their loss.
Overloading the existing structural system; or installing
equipment or mechanical systems which could damage the
Replacing a loadbearing masonry wall that could be
augmented and retained.
Leaving known structural problems untreated such as
deflection of beams, cracking and bowing of walls, or
racking of structural members.
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.
(left) At the New York State Capitol, non-destructive
testing techniques were used to determine existing
structural conditions and locate hidden structural
elements. (top right) The impact echo equipment
includes a hammer, receiver, and water soluble
gel and was used to locate a steel column concealed
behind the granite facing. (bottom right) Data
is shown on the computer field
screen. Photos: Marie Ennis, P.E.
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.
Repairing the structural system by augmenting or
upgrading individual parts or features in a manner that
is consistent with the restoration period. For example,
weakened structural members such as floor framing can
be paired with a new member, braced, or otherwise supplemented
and reinforced. The new work should be unobtrusively
dated to guide future research and treatment.
(bottom right) An oversized, classically detailed
sheet metal cornice is supported by steel trusses,
which are in turn attached to the structural steel
frame of the
building. (top left) The molding
applied to the modillions was
extremely deteriorated, requiring repair. (top
right) The cornice is shown after the repair work
and painting have been completed.
Photos: Richard Pieper.
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 that damages interior features or spaces.
Replacing a structural member or other feature of the
structural system when it could be augmented and retained.
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. The new work should be unobtrusively dated
to guide future research and treatment.
As part of the roof structure of early Southwest
adobe buildings, roughly dressed logs called "vigas"
rested either on the horizontal wooden member
which topped the adobe wall or on "corbels,"
which were set into the adobe wall. Traditionally,
these vigas often projected through the wall facades,
creating the typical adobe construction detail
copied in the 20th century revival styles. In
restoration, an extensively deteriorated viga
should be replaced in kind. (left) Viga logs on
inside of a historic adobe building (right); vigas
projecting through the wall facades of another
historic adobe building. Photos:
left: Russell Lee, Farm Security
Administration Collection, Library of Congress; right: NPS files.
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; or failing
to document the new work.
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 Restoration
work is highlighted to indicate that it involves
the removal or alteration of existing historic
structural systems and features that would be
retained in Preservation and Rehabilitation treatments;
and the replacement of missing structural system
features from the restoration period using all
Removing Existing Features from Other Historic
Removing or altering visually intrusive structural
features from other historic periods such as a
non-matching column or exposed ceiling beams.
Documenting materials and features dating
from other periods prior to their alteration or
removal. If possible, selected examples of these
features or materials should be stored to facilitate
Failing to remove or alter a visually intrusive
structural feature from another period, thus confusing
the depiction of the building's significance.
Failing to document structural features from
other historic periods that are removed from the
building so that a valuable portion of the historic
record is lost.
Re-creating Missing Features
from the Restoration Period
Re-creating a missing structural feature that
existed during the restoration period based on
physical or documentary evidence; for example,
duplicating a viga or cast iron column.
Constructing a structural feature that was part
of the original design for the building but was
never actually built; or constructing a feature
which was thought to have existed during the restoration
period, but for which there is insufficient documentation.