Guidelines For Rehabilitating Historic Buildings: Architectural Metals
- Procedure code:
- National Park Service, Preservation Assistance Division
- General Requirements
- Reference Standards
- Last Modified:
GUIDELINES FOR REHABILITATING HISTORIC BUILDINGS: ARCHITECTURAL
U.S. Department of the Interior
National Park Service
Preservation Assistance Division
An illustrated booklet addressing the Secretary's Standards and the
guidelines is available from the U.S. Government Printing Office.
The title is "The Secretary of the Interior's Standards for
Rehabilitation & Illustrated Guidelines for Rehabilitating Historic
Buildings", ISBN 0-16-035979-1.
Each of the guidelines included in the booklet mentioned above have
been separated into individual entries for specific use in HBPP.
This entry represents one of many guidelines included in the
booklet and describes RECOMMENDED and NOT RECOMMENDED applications
of the Secretary of the Interior's Standards as they relate to
Architectural Metals. For a list of the Secretary of the
Interior's Standards for Rehabilitation, see 01091-04-S; For
general information relating to the purpose, organization and
content of the individual guidelines, see 01091-05-S. Both of
these entries should be referenced along with the information
contained in this document.
ARCHITECTURAL METALS: Cast iron, steel, pressed tin, copper,
aluminum, and zinc
Architectural metal features -- such as cast-iron facades, porches,
and steps; sheet metal cornices, roofs, roof cresting and
storefronts; and cast or rolled metal doors, window sash,
entablatures, and hardware -- are often highly decorative and may
be important in defining the overall historic character of the
building. Their retention, protection, and repair should be a
prime consideration in rehabilitation projects.
IDENTIFYING, RETAINING AND PRESERVING
- Identifying, retaining, and preserving architectural
metal features such as columns, capitals, window hoods,
or stairways that are important in defining the overall
historic character of the building; and their finishes
- Removing or radically changing architectural metal
features which are important in defining the overall
historic character of the building so that, as a result,
the character is diminished.
- Removing a major portion of the historic architectural
metal from a facade instead of repairing or replacing
only the deteriorated metal, then reconstructing the
facade with new material in order to create a uniform, or
- Radically changing the type of finish or its historical
color or accent scheme.
PROTECTING AND MAINTAINING
- Protecting and maintaining architectural metals from
corrosion by providing proper drainage so that water does
not stand on flat, horizontal surfaces or accumulate in
curved, decorative features.
- Failing to identify, evaluate, and treat the causes of
corrosion, such as moisture from leaking roofs or
- Placing incompatible metals together without providing a
reliable separation material. Such incompatibility can
result in galvanic corrosion of the less noble metal,
e.g., copper will corrode cast iron, steel, tin, and
- Cleaning architectural metals, when necessary, to remove
corrosion prior to repainting or applying other
appropriate protective coatings.
- Exposing metals which were intended to be protected from
- Applying paint or other coatings to metals such as
copper, bronze, or stainless steel that were meant to be
- Identifying the particular type of metal prior to any
cleaning procedure and then testing to assure that the
gentlest cleaning method possible is selected or
determining that cleaning is inappropriate for the
- Using cleaning methods which alter or damage the historic
color, texture, and finish of the metal; or cleaning when
it is inappropriate for the metal.
- Removing the patina of historic metal. The patina may be
a protective coating on some metals, such as bronze or
copper, as well as a significant historic finish.
- Cleaning soft metals such as lead, tin, copper,
terneplate, and zinc with appropriate chemical methods
because their finishes can be easily abraded by blasting
- Cleaning soft metals such as lead, tin, copper,
terneplate, and zinc with grit blasting which will abrade
the surface of the metal.
- Using the gentlest cleaning methods for cast iron,
wrought iron, and steel -- hard metals -- in order to
remove paint buildup and corrosion. If handscraping and
wire brushing have proven ineffective, low pressure dry
grit blasting may be used as long as it does not abrade
or damage the surface.
- Failing to employ gentler methods prior to abrasively
cleaning cast iron, wrought iron or steel or using high
pressure grit blasting.
- Applying appropriate paint or other coating systems after
cleaning in order to decrease the corrosion rate of
metals or alloys.
- Failing to re-apply protective coating systems to metals
or alloys that require them after cleaning so that
accelerated corrosion occurs.
- Repainting with colors that are appropriate to the
historic building or district.
- Using new colors that are inappropriate to the historic
building or district.
- Applying an appropriate protective coating such as
lacquer to an architectural metal feature such as a
bronze door which is subject to heavy pedestrian use.
- Failing to assess pedestrian use or new access patterns
so that architectural metal features are subject to
damage by use or inappropriate maintenance such as
salting adjacent sidewalks.
- Evaluating the overall condition of the architectural
metals to determine whether more than protection and
maintenance are required, that is, if repairs to features
will be necessary.
- Failing to undertake adequate measures to assure the
preservation of architectural metal features.
- Repairing architectural metal features by patching,
splicing, or otherwise reinforcing the metal following
recognized preservation methods. Repairs may also
include the limited replacement in kind -- or with a
compatible substitute material -- of those extensively
deteriorated or missing parts of features when there are
surviving prototypes such as porch balusters, column
capitals or bases; or porch cresting.
- Replacing an entire architectural metal features such as
a column or a balustrade when repair of the metal and
limited replacement of deteriorated or missing parts are
- Using a substitute material for the replacement part that
does not convey the visual appearance of the surviving
parts of the architectural metal feature or that is
physically or chemically incompatible.
- Replacing in kind an entire architectural metal feature
that is too deteriorated to repair -- if the overall form
and detailing are still evident -- using the physical
evidence to guide the new work. Examples could include
cast iron porch steps or steel sash windows. If using
the same kind of material is not technically or
economically feasible, then a compatible substitute
material may be considered.
- Removing an architectural metal feature that is
unrepairable and not replacing it; or replacing it with
a new architectural metal feature that does not convey
the same visual appearance.
NOTE: THE FOLLOWING REPRESENTS PARTICULARLY COMPLEX TECHNICAL OR
DESIGN ASPECTS OF REHABILITATION PROJECTS AND SHOULD ONLY BE
CONSIDERED AFTER THE PRESERVATION CONCERNS LISTED ABOVE HAVE BEEN
DESIGN FOR MISSING HISTORIC FEATURES
- Designing and installing a new architectural metal
feature such as a sheet metal cornice or cast iron
capital when the historic feature is completely missing.
It may be an accurate restoration using historical,
pictorial and physical documentation; or be a new design
that is compatible with the size, scale, material, and
color of the historic building.
- Creating a false historic appearance because the replace
architectural metal feature is based on insufficient
historical, pictorial, and physical documentation.
- Introducing a new architectural metal feature that is
incompatible in size, scale, material, and color.
END OF SECTION