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Historic Preservation - Technical Procedures

Spectitle:

Guidelines For Rehabilitating Historic Buildings: Wood

Procedure code:

0109107S

Source:

National Park Service, Preservation Assistance Division

Division:

General Requirements

Section:

Reference Standards

Last Modified:

02/24/2012

Details:

Guidelines For Rehabilitating Historic Buildings: Wood



GUIDELINES FOR REHABILITATING HISTORIC BUILDINGS:  WOOD


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
Wood.  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

WOOD:  Clapboard, weatherboard, shingles, and other wooden siding
and decorative elements

Because it can be easily shaped by sawing, planing, carving, and
gouging, wood is the most commonly used material for architectural
features such as clapboards, cornices, brackets, entablatures,
shutters, columns and balustrades.  These wooden features - both
functional and decorative - may be important in defining the
historic character of the building and thus their retention,
protection, and repair are of particular importance in
rehabilitation projects.


IDENTIFYING, RETAINING AND PRESERVING

1.   Recommended:

    -    Identifying, retaining, and preserving wood features that
         are important in defining the overall historic character
         of the building such as siding, cornices, brackets,
         window architraves, and doorway pediments; and their
         paints, finishes, and colors.

    Not Recommended:

    -    Removing or radically changing wood 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 wood from a
         facade instead of repairing or replacing only the
         deteriorated wood, then reconstructing the facade with
         new material in order to achieve a uniform or "improved"
         appearance.

    -    Radically changing the type of finish or its color or
         accent scheme so that the historic character of the
         exterior is diminished.

    -    Stripping historically painted surfaces to bare wood,
         then applying clear finishes or stains in order to create
         a "natural look."

    -    Stripping paint or varnish to bare wood rather than
         repairing or reapplying a special finish, i.e., a grained
         finish to an exterior wood feature such as a front door.


PROTECTING AND MAINTAINING

1.   Recommended:  

    -    Protecting and maintaining wood features by providing
         proper drainage so that water is not allowed to stand on
         flat, horizontal surfaces or accumulate in decorative
         finishes.

    Not Recommended:

    -    Failing to identify, evaluate, and treat the causes of
         wood deterioration, including faulty flashing, leaking
         gutters, cracks and holes in siding, deteriorated
         caulking in joints and seams, plant material growing too
         close to wood surfaces, or insect or fungus infestation.

2.   Recommended:

    -    Applying chemical preservatives to wood features such as
         beam ends or outriggers that are exposed to decay hazards
         and are traditionally unpainted.

    Not Recommended:

    -    Using chemical preservatives such as creosote which can
         change the appearance of wood features unless they were
         used historically.  

3.   Recommended:

    -    Retaining coatings such as paint that help protect the
         wood from moisture and ultraviolet light.  Paint removal
         should be considered only where there is paint surface
         deterioration and as part of an overall maintenance
         program which involves repainting or applying other
         appropriate protective coatings.

    Not Recommended:

    -    Stripping paint or other coatings to reveal bare wood,
         thus exposing historically coated surfaces to the effects
         of accelerated weathering.

4.   Recommended:

    -    Inspecting painted wood surfaces to determine whether
         repainting is necessary or if cleaning is all that is
         required.

    Not Recommended:

    -    Removing paint that is firmly adhering to, and thus,
         protecting wood surfaces.

5.   Recommended:

    -    Removing damaged or deteriorated paint to the next sound
         layer using the gentlest method possible (handscraping
         and handsanding), then repainting.

    Not Recommended:

    -    Using destructive paint removal methods such as  propane
         or butane torches, sandblasting or waterblasting.  These
         methods can irreversibly damage historic woodwork.

6.   Recommended:

    -    Using with care electric hot-air guns on decorative wood
         features and electric heat plates on flat wood surfaces
         when paint is so deteriorated that total removal is
         necessary prior to repainting.

    Not Recommended:

    -    Using thermal devices improperly so that the historic
         woodwork is scorched.

7.   Recommended:

    -    Using chemical strippers primarily to supplement other
         methods such as handscraping, handsanding and the above-
         recommended thermal devices.  Detachable wooden elements
         such as shutters, doors, and columns may -- with the
         proper safeguards -- be chemically dip-stripped.

    Not Recommended:

    -    Failing to neutralize the wood thoroughly after using
         chemicals so that new paint does not adhere.

    -    Allowing detachable wood features to soak too long in a
         caustic solution so that the wood grain is raised and the
         surface roughened.

8.   Recommended:

    -    Applying compatible paint coating systems following
         proper surface preparation.

    Not Recommended:

    -    Failing to follow manufacturers' product and application
         instructions when repainting exterior woodwork.

9.   Recommended:

    -    Repainting with colors that are appropriate to the
         historic building and district.

    Not Recommended:

    -    Using new colors that are inappropriate to the historic
         building or district.

10.  Recommended:

    -    Evaluating the overall condition of the wood to
         determine whether more than protection and maintenance
         are required, that is, if repairs to wood features will
         be necessary.

    Not Recommended:

    -    Failing to undertake adequate measures to assure the
         preservation of wood features.


REPAIRING

1.   Recommended:

    -    Repairing wood features by patching, piecing-in,
         consolidating, or otherwise reinforcing the wood using
         recognized preservation methods.  Repair may also include
         the limited replacement in kind -- or with compatible
         substitute material -- of those extensively deteriorated
         or missing parts of features where there are surviving
         prototypes such as brackets, moldings, or sections of
         siding.

    Not Recommended:

    -    Replacing an entire wood feature such as a cornice or
         wall when repair of the wood and limited replacement of
         deteriorated or missing parts are appropriate.

    -    Using substitute materials for the replacement part that
         does not convey the visual appearance of the surviving
         parts of the wood feature or that is physically or
         chemically incomparable.


REPLACING

1.   Recommended:  

    -    Replacing in kind an entire wood 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 of wood
         features include a cornice, entablature or balustrade.
         If using the same kind of material is not technically or
         economically feasible, then a compatible substitute
         material may be considered.

    Not Recommended:

    -    Removing an entire wood feature that is unrepairable 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 installing a new wood feature such as a
         cornice or doorway when the historic features 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.

    Not Recommended:

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

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

                         END OF SECTION