Preservation Briefs: 35 Understanding Old Buildings: The Process Of Architectural Investigation

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National Park Service, Preservation Assistance Division
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The link immediately connects to the latest version of National Park Service Brief 35:

Travis C. McDonald, Jr.

This standard includes the bulk of information contained in the
original Preservation Brief developed by the National Park Service.
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If you have ever felt a sense of excitement and mystery going
inside an old building--whether occupied or vacant--it is probably
because its materials and features resonate with the spirit of past
people and events.  Yet excitement about the unknown is heightened
when a historic structure is examined architecturally, and its
evolution over time emerges with increasing clarity to reveal the
lives of its occupants.  Architectural investigation is the
critical first step in planning an appropriate treatment--understanding
how a building has changed over time and assessing levels of deterioration.

Whether as a home owner making sympathetic repairs, a craftsman or
contractor replacing damaged or missing features, or a conservator
reconstituting wood or restoring decorative finishes, some type of
investigative skill was used to recognize and solve an
architectural question or explain a difficult aspect of the work

To date, very little has been written for the layman on the subject
of architectural investigation.  This Preservation Brief thus
addresses the often complex investigative process in broad,
easy-to-understand terminology.  The logical sequence of planning,
investigation and analysis presented in this Brief is applicable to
all buildings, geographic locations, periods, and construction
types.  It is neither a "how to" nor an exhaustive study on
techniques or methodologies; rather, it serves to underscore the
need for meticulous planning prior to work on our irreplaceable
cultural resources.


Both the purpose and scope of investigation need to be determined
before formulating a particular approach.  For example,
investigation strictly for research purposes could produce
information for an architectural survey or for an historic
designation application at the local, state or national level.

Within the framework of The secretary of the Interior's Standards
for the Treatment of Historic Properties, investigation is crucial
for "identifying, retaining, and preserving the form and detailing
of those architectural materials and features that are important in
defining the historic character" of a property, whether for repair
or replacement.  A rehabilitation project, for instance, might
require an investigation to determine the historic configuration of
interior spaces prior to partitioning a room to meet a compatible
new use.  Investigation for preservation work can entail more
detailed information about an entire building, such as determining
the physical sequence of construction to aid in interpretation.
Investigation for a restoration project must be even more
comprehensive in order to re-capture the exact form, features,
finishes, and detailing of every component of the building.

Whether investigation will be undertaken by professionals--architects,
conservators, historians--or by interested homeowners,
the process is essentially comprised of a preliminary four-step
procedure:  historical research, documentation, inventory, and


Primary historical research of an old building generally
encompasses written, visual and oral resources that can provide
valuable site-specific information.  Written resources usually
include letters, legal transactions, account books, insurance
policies, institutional papers, and diaries.  Visual resources
consist of drawings, maps, plats, paintings and photographs.  Oral
resources are people's remembrances of the past.  Secondary
resources, comprised of research or history already compiled and
written about a subject, are also important for providing a broad
contextual setting for a project.

Historical research should be conducted well in advance of physical
investigation.  This allows time for important written, visual, and
oral information to be located, transcribed, organized, studied and
used for planning the actual work.

A thorough scholarly study of a building's history provides a
responsible framework for the physical investigation; in fact, the
importance of the link between written historical research and
structural investigation cannot be overestimated.  For example, the
historical research of a building through deed records may merely
determine the sequence of owners.  This, in turn, aids the
investigation of the building by establishing a chronology and
identifying the changes each occupant made to the building.  A
letter may indicate that an occupant painted the building in a
certain year; the courthouse files contain the occupant's name and
paint analysis of the building will yield the actual color.  Two-
dimensional documentary research and three-dimensional physical
investigation go hand-in-hand in analyzing historic structures.
The quality and success of any restoration project is founded upon
the initial research.


A building should be documented prior to any inventory,
stabilization or investigative work in order to record crucial
material evidence.  A simple, comprehensive method is to take 35 mm
photographs of every wall elevation (interior and exterior), as
well as general views, and typical and unusual details.  The
systematic numbering of rooms, windows and doors on the floor plan
will help organize this task and also be useful for labelling the
photographs.  Video coverage with annotated sound may supplement
still photographs.  Additional methods of documentation include
written descriptions, sketches, and measured drawings.

Significant structures, such as individually listed National
Register properties or National Historic Landmarks, benefit from
professional photographic documentation and accurate measured
drawings.  Professional frequently use The Secretary of the
Interior's Standards and Guidelines for Architectural and
Engineering Documentation:  HABS/HAER Standards.  It should be
remembered that the documents created during investigation might
play an unforeseen role in future treatment and interpretation.
Documentation is particularly valuable when a feature will be
removed or altered.


The historic building and its components should be carefully
inventoried prior to taking any action; premature clean-up of a
structure or site can be a mistake.  A careful look at all spaces
in and around a building may reveal loose architectural artifacts,
fragile evidence or clues to historic landscape features.  This
thorough observation includes materials and features which have
fallen off due to deterioration, fragments removed and stored in
basements, attics or outbuildings, and even materials which have
seemingly been discarded.

In the beginning, anything that seems even remotely meaningful
should be saved.  A common mistake is to presume to know the value
of artifacts or features at the beginning of a project.  Even if
the period of significance or interpretation is known from the
beginning, evidence from all periods should be protected.
Documentation for future study or use includes labelling and, if
possible, photographing prior to storage in a secure place.


In many cases, emergency stabilization is necessary to ensure that
a structure does not continue to deteriorate prior to a final
treatment or to ensure the safety of current occupants,
investigators, or visitors.  Although severe cases might call for
structural remedies, in more common situations, preliminary
stabilization would be undertaken on a maintenance level.  Such
work could involve installing a temporary roof covering to keep
water out; diverting water away from foundation walls; removing
plants that hold water too close to the walls; or securing a
structure against intruding insects, animals and vandals.

An old building may require temporary remedial work on exterior
surfaces such as reversible caulking or an impermanent,
distinguishable mortar.  Or if paint analysis is contemplated in
the future, deteriorated paint can be protected without heavy
scraping by applying a recognizable "memory" layer over all the
historic layers.  Stabilization adds to the cost of any project,
but human safety and the protection of historical evidence are well
worth the extra money.



The essential skill needed for any level of investigation is the
ability to observe closely and to analyze.  These qualities are
ideally combined with a hands-on familiarity of historic buildings
-- and an open mind!  Next, whether acquired in a university or in
a practical setting, an investigator should have a good general
knowledge of history, building design history and, most important,
understand both construction and finish technologies.

But it is not enough to know architectural style and building
technology from a national viewpoint; the investigator needs to
understand regional and local differences as well.  While
investigative skills are transferable between regions and
chronological periods, investigators must be familiar with the
peculiarities of any given building type and geographical area.

Architectural survey and comparative fieldwork provides a crucial
database for studying regional variations in historic buildings.
For example, construction practices can reflect shared experiences
of widely diverse backgrounds and traditions within a small
geographical area.  Contemporary construction practice in an urban
area might vary dramatically from that of rural areas in the same
region.  Neighbors or builders within the same geographical area
often practice different techniques of constructing similar types
of structures contemporaneously.  Reliable dating clues for a
certain brick bond used in one state might be unreliable for the
same period in a different state.  Regional variation holds true
for building materials as well as construction.

Finally, even beyond regional and local variation, an investigator
needs to understand that each building has its own unique history
of construction and change over time.  Form, features, materials
and detailing often varied according to the tastes and finances of
both builder and supplier; construction quality and design were
also inconsistent, as they are today.


Because architectural investigation requires a wide range of
knowledge and many different skills various people are likely to
interact on the same project.  While homeowners frequently execute
small-scale projects, more complex projects might be directed by a
craftsperson, an architect or a conservator.  For large-scale
projects, a team approach may need to be adopted, consisting of
professionals, architectural conservators, craftspersons, historic
finish analysts, historians, archeologists, architects, curators,
and many others.  The scope and needs of a specific project dictate
the skills of key players.

Architectural investigation often includes the related fields of
landscape and archeological investigation.  Landscape survey or
analysis by horticulturists and landscape architects identify pre-existing
features or plantings or those designed as separate or
complementary parts of the site.  Both above and below-ground
archeology contribute information about missing or altered
buildings, construction techniques, evidence of lifestyle and
material culture, and about the evolution of the historic landscape


Although brick or wood frame buildings are the most common in this
country, similar sets of characteristics and questions can be
established for examining log, adobe, steel, or any other material.


Studying historic brickwork can provide important information about
methods of production and construction.  For example, the color,
size, shape and texture of brick reveals whether it was hand molded
and traditionally fired in a clamp with hardwoods, or whether it
was machine molded and fired in a kiln using modern fuels.
Similarly, the principal component part of masonry mortar, the lime
or cement, reveals whether it was produced in a traditional or
modern manner.  Certain questions need to be asked during
investigation.  Is the mortar made with a natural or a Portland
cement?  If a natural cement, did it come from an oyster shell or
a limestone source?  Is it hydrated or hydraulic?  As a
construction unit, brick and mortar further reveal something about
the time, place and human variables of construction, such as the
type of bond, special brick shapes, decorative uses of glazed or
rubbed brick, coatings and finishes, and different joints, striking
and tooling.  Does the bond conform with neighboring or regional
buildings of the same period?  Does the pattern of "make up" bricks
in a Flemish Bond indicate the number of different bricklayers?
What is the method of attaching wood trim to the masonry?  The same
types of Questions related to production and construction
characteristics can be applied to all types of masonry work,
including stone, concrete, terra cotta, adobe and coquina
construction.  A complete survey undertaken during "surface
mapping" can outline the materials and construction practices for
the various periods of a structure, distinguishing the original
work as well as the additions, alterations, and replacements.


Buildings constructed with wood have a very different set of
characteristics, requiring a different line of questioning.  Is the
wooden structural system log, timber frame, or balloon frame
construction?  Evidence seen on the wood surface indicates whether
production was by ax, adze, pit saw, mill saw (sash or circular),
or band saw.  What are the varying dimensions of the lumber used?
Finished parts can be sawn, gouged, carved, or planed (by hand or
by machine).  Were they fastened by notching, mortise and tenon,
pegs, or nailing?  If nails were used, were they wrought by hand,
machine cut with wrought heads, entirely machine cut, or machine
wire nails?  For much of the nineteenth century the manufacture of
nails underwent a series of changes and improvements that are
dateable, allowing nails to be used as a tool in establishing
periods of construction and alteration.  Regardless of region or
era, the method of framing, joining and finishing a wooden
structure will divulge something about the original construction,
its alterations, and the practices of its builders.  Finally, does
some of the wood appear to be reused or recycled?  Reused and
reproduction materials used in early restoration projects have
confused many investigators.  When no identification record was
kept, it can be a problem distinguishing between materials original
to the house and later replacement materials.


Exterior features are especially prone to alteration due to
weathering and lack of maintenance.  Even in the best preserved
structures, the exterior often consists of replaced or repaired
roofing parts.  Roof coverings typically last no more than fifty
years.  Are several generation of roof coverings still in place?
Can the layers be identified?  If earlier coverings were removed,
the sheathing boards frequently provide clues to the type of
covering as well as missing roof features.  Dormers, cupolas,
finials, cresting, weathervanes, gutters, lightning rods,
skylights, balustrades, parapets and platforms come and go as
taste, function and maintenance dictate.  The roof pitch itself can
be a clue to stylistic dating and is unlikely to change unless the
entire roof has been rebuilt.  Chimneys might hold clues to
original roof pitch, flashings, and roof feature attachments.  Is
it possible to look down a chimney and count the number of flues?
This practice has occasionally turned up a missing fireplace.  In
many parts of the country, nineteenth-century roof coverings
evolved from wooden shingles or slate shingles, to metal shingles,
to sheet metal, and still later in the twentieth century, to
asphaltic or asbestos shingles.  Clay tiles can be found covering
roofs in seventeenth and eighteenth-century settlements of the east
coast as well as western and southwestern Spanish settlements from
the same period.  Beyond the mid-nineteenth century, and into the
twentieth, the range and choice of roof coverings greatly expanded.


In addition to production and construction clues, floors reveal
other information about the interior, such as circulation patterns,
furniture placement, the use of carpets, floor cloths, and applied
floor finishes.  Is there a pattern of tack holes?  Tacks or tack
holes often indicate the position and even the type of a floor
covering.  A thorough understanding of the seasonal uses of floor
coverings and the technological history of their manufacture
provide the background for identifying this type of evidence.


Walls and their associated trim, both outside and inside, hold many
clues to the building's construction and changes made over time.
The overall style of moldings, trim and finishes, and their
hierarchical relationship, can help explain original construction
as well as room usage and social interaction between rooms.  Holes,
scars, patches, nails, nail holes, screws and other hardware
indicate former attachments.  Are there "ghosts," or shadow
outlines of missing features, or trim attachments such as bases,
chair rails, door and window casings, entablatures, cornices,
mantels and shelves?  Ghosts can be formed by paint, plaster,
stucco, wear, weathering or dirt.  Interior walls from the
eighteenth and early nineteenth-century were traditionally
plastered after grounds or finished trim was in place, leaving an
absence of plaster on the wall behind them.  Evidence of
attachments on window casings can also be helpful in understanding
certain interior changes.  Other clues to look for include the
installation of reused material brought into a house or moved about
within a house; worker's or occupant's graffiti, especially on the
back of trim; and hidden finishes or wallpaper stuck in crevices or
underneath pieces of trim.  Stylistic upgrading often resulted in
the reuse of outdated trim for blocking or shims.  Unexpected
discoveries are particularly rewarding.  Investigators frequently
tell stories about clues that were uncovered from architectural
fragments carried off by rats and later found, or left by workers
in attics, between walls and under floors.


Attics and basements have been known as collection points for
out-of-date, out-of-style and cast-off pieces such as mechanical
systems, furnishings, family records and architectural fragments.
These and other out-of-the-way places of a structure provide an
excellent opportunity for non-destructive investigation.  Not only
are these areas where structural and framing members might be
exposed to view, they are also areas which may have escaped the
frequent alteration campaigns that occur in the more lived-in parts
of a building.  If a building has been raised or lowered in height,
evidence of change would be found in the attic as well as on the
exterior.  Evidence of additions might also be detected in both the
attic and basement.  Attics frequently provide a "top-side" view at
the ceiling below, revealing its material, manner of production and
method of attachment.  A "bottom-side" view of the roof sheathing
or roof covering can be seen from the attic as well.

Basements generally relate more to human service functions in
earlier buildings and to mechanical services in more recent areas.
For example, A cellar of an urban 1812 house disclosed the
following information during an investigation:  first period bell
system, identification of a servant's hall, hidden fireplace,
displacement of the service stairs, identification of a servants'
quarters, an 1850s furnace system, 1850s gas and plumbing systems,
relocation of the kitchen in 1870, early use of 1890s concrete
floor slabs and finally, twentieth century utility systems.  While
the earliest era had been established as the interpretation period,
evidence from all periods was documented in order to understand and
interpret how the house evolved or changed over time.


Systems of utility and convenience bear close scrutiny during
investigation.  All historic buildings inhabited and used by people
reveal some association, at the very minimum, with the necessities
of lighting, climate control, water, food preparation, and waste
removal.  Later installations in a building may include
communication, hygiene, food storage, security, and lightning
protection systems.  Other systems, such as transportation, are
related to more specific functions of commercial or public
structures.  Although research into the social uses of rooms and
their furnishings has borne many new studies, parallel research
into how people actually carried out the most mundane tasks of
everyday life has been fairly neglected.  Utility and convenience
systems are most prone to alteration and upgrading and, at the same
time, less apt to be preserved, documented or re-used.
Understanding the history or use of a building, and the history of
systems technology can help predict the physical evidence that
might be found, and what it will look like after it is found.



Research prior to investigation may have indicated the architect,
builder or a building's date of construction.  In the absence of
such information, architectural histories and field guides to
architectural style can help identify a structure's age through its
form and style.

Any preliminary date, however, has to be corroborated with other
physical or documentary facts.  Dates given for stylistic periods
are general and tend to be somewhat arbitrary, with numerous local
variations.  Overall form and style can also be misleading due to
subsequent additions and alterations.  When the basic form seems in
conflict with the details, it may indicate a transition between
styles or that a style was simply upgraded through new work.

The architectural investigation usually determines original
construction details, the chronology of later alterations, and the
physical condition of a structure.  Most structures over fifty
years old have been altered, even if only by natural forces.
People living in a house or using a building for any length of time
leave some physical record of their time there, however subtle.  A
longer period of occupancy generally counts for greater physical
change.  Buildings acquire a "historic character" as changes are
made over time.

Changes to architectural form over time are generally attributable
to material durability, improvement in convenience systems, and
aesthetics.  First the durability of building materials is affected
by weathering, temperature and humidity, by disasters such as
storms, floods or fire, or by air pollution from automobiles and
industry.  Second, changes in architectural form have always been
made for convenience sake -- fueled by technological innovations --
as people embrace better lighting, plumbing, heating, sanitation,
and communication.  People alter living spaces to meet changing
family needs.  Finally, people make changes to architectural form,
features, and detailing to conform to current taste and style.


Architectural investigation can range from a simple one hour
walk-through to a month long or even multi-year project -- and varies
from looking at surfaces to professional sub-surface examination
and laboratory work.

All projects should begin with the simplest, non-destructive
processes and proceed as necessary.  The sequence of investigation
starts with reconnaissance and progresses to surface examination
and mapping, sub-surface non-destructive testing, and various
degrees of sub-surface destructive testing.


An initial reconnaissance trip through a structure -- or visual
overview -- provides the most limited type of investigation.  But
experienced investigators accustomed to observation and analysis
can resolve many questions in a two-to-four hour preliminary site
visit.  They may be able to determine the consistency of the
building's original form and details as well as major changes made
over time.


The first step in a thorough, systematic investigation is the
examination of all surfaces.  Surface investigation is sometimes
called "surface mapping" since it entails a minute look at all the
exterior and interior surfaces.  The fourfold purpose of surface
mapping is to observe every visible detail of design and
construction; develop questions related to evidence and possible
alterations; note structural or environmental problems; and help
develop plans for any further investigation.  Following
investigation, a set of documentary drawings and photographs is
prepared which record or "map" the evidence.

While relying upon senses of sight and touch, the most useful tool
for examining surfaces is a high-powered, portable light used for
illuminating dark spaces as well as for enhancing surface
subtleties.  Raking light at an angle on a flat surface is one of
the most effective means of seeing evidence of attachments, repairs
or alterations.


The next level of investigation consists of probing beneath
surfaces using non-destructive methods.  Questions derived from the
surface mapping examination and analysis will help determine which
areas to probe.  Investigators have perfected a number of tools and
techniques which provide minimal damage to historic fabric.  These
include x-rays to penetrate surfaces in order to see nail types and
joining details; boroscopes, fiber optics and small auto mechanic
or dentists' mirrors to look inside of tight spaces; and ultra-violet or
infra-red lights to observe differences in materials and
finishes.  The most advanced technology combines the boroscope with
video cameras using fiber optic illumination.  In addition to the
more common use of infra-red photography, similar non-destructive
techniques used in archeological investigations include remote
sensing and ground-penetrating radar.

Small material samples of wood, plaster, mortar, or paint can also
be taken for laboratory analysis at this stage of investigation.
For instance, a surface examination of a plaster wall using a
raking light may show clear evidence of patching which corresponds
to a shelf design.  Were the shelves original or a later addition?
A small sample of plaster from the patched area is analyzed in the
laboratory and matches plaster already dated to a third period of
construction.  A probe further reveals an absence of first period
plaster on the wall underneath.  The investigator might conclude
from this evidence that the shelves were an original feature and
that the plaster fill dates their removal and patching to a third
period of construction.


Most investigations require nothing more than historical research,
surface examination and non-destructive testing.  In very rare
instances the investigation may require a sub-surface examination
and the removal of fabric.  Destructive testing should be carried
out by a professional only after historical research and surface
mapping have been fully accomplished and only after non-destructive
testing has failed to produce the necessary information.  Owners
should be aware that the work is a form of demolition in which the
physical record may be destroyed.  Sub-surface examination begins
with the most accessible spaces, such as retrofitted service and
mechanical chases; loose or previously altered trim, ceilings or
floor boards; and pieces of trim or hardware which can be easily
removed and replaced.

Non-destructive testing techniques do not damage historic fabric.
If non-destructive techniques are not sufficient to resolve
important questions, small "windows" can be opened in surface
fabric at predetermined locations to see beneath the surface.  This
type of subsurface testing and removal is sometimes called
"architectural archeology" because of its similarity to the more
well-known process of trenching in archeology.  The analogy is apt
because both forms of archeology use a method of destructive

Photographs, video and drawings should record the before, during
and after evidence when the removal of historic fabric is
necessary.  The selection and sequence of material to be removed
requires careful study so that original extant fabric remains in
situ if possible.  If removed, original fabric should be carefully
put back or labelled and stored.  At least one documentary patch of
each historic finish should be retained in situ for future
research.  Treatment and interpretation, no matter how accurate,
are usually not final; treatment tends to by cyclical, like
history, and documentation must be left for future generations,
both on the wall and in the files.


Laboratory analysis plays a scientific role in the more intuitive
process of architectural investigation.  One of the most commonly
known laboratory procedures used in architectural investigation is
that of historic paint analysis.  The chronology and stratigraphy
of applied layers can establish appropriate colors, finishes,
designs or wall coverings.  When conducted simultaneously with
architectural investigation, the stratigraphy of finishes, like
that of stratigraphic soils in archeology, helps determine the
sequence of construction or alterations in a building.  Preliminary
findings from in situ examinations of painted finishes on walls or
trim are common, but more accurate results come from extensive
sampling and microscopic laboratory work using chemical analysis
and standardized color notations.  Consultants without the proper
knowledge have been known to cause far more harm than good.

Mortar and plaster analysis often provide a basis for dating
construction with minimal intervention.  Relatively small samples
of the lime-based materials can be chemically separated into their
component parts of sands and fines, which are then visually
compared to equivalent parts of known or dated samples.  A more
thorough scientific approach may be used to accurately profile and
compare samples of other materials through elemental analysis.  Two
similar methods in common use are Neutrol Activation and Energy
Dispersive Spectroscopy (EDS).  Neutron Activation identifies the
sample's trace elements by monitoring their response to neutron
bombardment.  EDS measures the response to electron bombardment

Last Reviewed 2012-09-05