Detail of restored roof; Link to Parknet
STANDARDS FOR RESTORATION AND GUIDELINES FOR RESTORING HISTORIC BUILDINGS
<photo>wood structural members of an early industrial building

Identify    Protect    Repair    Replace    Remove   Re-Create

Identify, Retain and Preserve

Recommend
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 walls.

photo of exterior stone walls that comprise the structural system of a small farm building

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, NPS.

Not Recommended
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 structure.

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

Recommend
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.

photo series showing the process of non-destructive testing of structural conditions at the New York State Capitol

(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.

Not Recommended
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

Recommend
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.

photos before and after the restoration of a sheet metal cornice

(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.

Not Recommended
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.

Replace

Recommend
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.

photos showing how vigas are part of the roof structure of early Southwest adobe buildings

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.

Not Recommended
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 new materials..

Removing Existing Features from Other Historic Periods

Recommend
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 future research.

Not Recommended
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

Recommend
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.

Not Recommended
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.

 

-GUIDELINES-

The Approach

Exterior Materials
Masonry
Wood
Architectural Metals

Exterior Features
Roofs
Windows
Entrances + Porches
Storefronts

Interior Features
Structural System Spaces/Features/Finishes
Mechanical Systems

Site

Setting

Special Requirements
Energy Efficiency
Accessibility
Health + Safety

The Standards

 

  HISTORICAL OVERVIEW - PRESERVING - REHABILITATING - restoring- RECONSTRUCTING

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Historical Overview