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Historic Preservation - Technical Procedures

Spectitle:
Guidelines For Rehabilitating Historic Buildings: Roofs

Procedure code:
0109109S

Source:
National Park Service, Preservation Assistance Division

Division:
General Requirements

Section:
Reference Standards

Last Modified:
02/24/2012

Details:
Guidelines For Rehabilitating Historic Buildings: Roofs



GUIDELINES FOR REHABILITATING HISTORIC BUILDINGS:  ROOFS


U.S. Department of the Interior
National Park Service
Preservation Assistance Division
Washington, D.C.


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
Roofs.  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.


BUILDING EXTERIOR

ROOFS:

The roof -- with its shape; features such as cresting, dormers,
cupolas, and chimneys; and the size, color, and patterning of the
roofing material -- can be extremely important in defining the
building's overall historic character.  In addition to the design
role it plays, a weathertight roof is essential to the preservation
of the entire structure; thus, protecting and repairing the roof as
a "cover" is a critical aspect of every rehabilitation project.


IDENTIFYING, RETAINING AND PRESERVING

1.   Recommended:

    -    Identifying, retaining, and preserving roofs -- and their
         functional and decorative features -- that are important
         in defining the overall historic character of the
         building.  This includes the roof's shape, such as
         hipped, gambrel, and mansard; decorative features such as
         cupolas, cresting, chimneys, and weathervanes; and
         roofing material such as slate, wood, clay tile, and
         metal, as well as its size, color, and patterning.

    Not Recommended:

    -    Radically changing, damaging, or destroying roofs 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 roof or roofing material
         that is repairable, then reconstructing it with new
         material in order to create a uniform, or "improved"
         appearance.

    -    Changing the configuration of a roof by adding new
         features such as dormer windows, vents, or skylights so
         that the historic character is diminished.

    -    Stripping the roof of sound historic material such as
         slate, clay tile, wood, and architectural metal.

    -    Applying paint or other coatings to roofing material
         which has been historically uncoated.


PROTECTING AND MAINTAINING

1.   Recommended:

    -    Protecting and maintaining a roof by cleaning the gutters
         and downspouts and replacing deteriorated flashing.  Roof
         sheathing should also be checked for proper venting to
         prevent moisture condensation and water penetration; and
         to insure that materials are free from insect
         infestation.

    Not Recommended:

    -    Failing to clean and maintain gutters and downspouts
         properly so that water and debris collect and cause
         damage to roof fasteners, sheathing, and the underlying
         structure.

2.   Recommended:

    -    Providing adequate anchorage for roofing material to
         guard against wind damage and moisture penetration.

    Not Recommended:

    -    Allowing roof fasteners, such as mails and clips to
         corrode so that roofing material is subject to
         accelerated deterioration.

3.   Recommended:

    -    Protecting a leaking roof with plywood and building paper
         until it can be properly repaired.

    Not Recommended:

    -    Permitting a leaking roof to remain unprotected so that
         accelerated deterioration of historic building materials
         -- masonry, wood, plaster, paint and structural members
         -- occurs.


REPAIRING

1.   Recommended:

    -    Repairing a roof by reinforcing the historic materials
         which comprise roof features.  Repairs will also
         generally include the limited replacement in kind -- or
         with compatible substitute material -- of those
         extensively deteriorated or missing parts of features
         when there are surviving prototypes such as cupola
         louvers, dentils, dormer roofing; or slates, tiles, or
         wood shingles on a main roof.

    Not Recommended:

    -    Replacing an entire roof feature such as a cupola or
         dormer when repair of the historic materials and limited
         replacement of deteriorated or missing parts are
         appropriate.

    -    Using a substitute material for the replacement part that
         does not convey the visual appearance of the surviving
         parts of the roof or that is physically or chemically
         incompatible.


REPLACING

1.   Recommended:

    -    Replacing in kind an entire feature of the roof that is
         too deteriorated to repair -- if the overall form and
         detailing are still evidence -- using the physical
         evidence to guide the new work.  Examples can include a
         large section of roofing, or a dormer or chimney.  If
         using the same kind of material is not technically or
         economically feasible, then a compatible substitute
         material may be considered.

    Not Recommended:

    -    Removing a feature of the roof that is unrepairable, such
         as a chimney or dormer, and not replacing it; or
         replacing it with a new 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
ADDRESSED.

DESIGN FOR MISSING HISTORIC FEATURES

1.   Recommended:

    -    Designing and constructing a new feature when the
         historic feature is completely missing, such as a chimney
         or cupola.  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.

    Not Recommended:

    -    Creating a false historical appearance because the
         replace feature is based on insufficient historical,
         pictorial, and physical documentation.

    -    Introducing a new roof feature that is incompatible in
         size, scale, material, and color.


ALTERATIONS/ADDITIONS FOR THE NEW USE

1.   Recommended:

    -    Installing mechanical and service equipment on the roof
         such as air conditioning, transformers, or solar
         collectors when required for the new use so that they are
         inconspicuous from the public right-of-way and do not
         damage or obscure character-defining features.

    Not Recommended:

    -    Installing mechanical or service equipment so that it
         damages or obscures character-defining features; or is
         conspicuous from the public right-of-way.

2.   Recommended:

    -    Designing additions to roofs such as residential, office,
         or storage spaces; elevator housing; decks and terraces;
         or dormers or skylights when required by the new use so
         that they are inconspicuous from the public right-of-way
         and do not damage or obscure character-defining features.

    Not Recommended:

    -    Radically changing a character-defining roof shape or
         damaging or destroying character-defining roofing
         material as a result of incompatible design or improper
         installation techniques.

                         END OF SECTION