35 PRESERVATION 

BRIEFS 

Understanding Old Buildings: 

The Process of Architectural Investigation 

Travis C. McDonald, Jr. 

U.S. Department of the Interior 

National Park Service 

Cultural Resources 

Heritage Preservation Services 

If you have ever felt a sense of excitement and mystery 

going inside an old building-whether occupied or vacantit 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 itself. 

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. 

Determining the Purpose of Investigation 

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 surveyor 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 professionalsarchitects, conservators, historians-or by interested 

homeowners, the process is essentially comprised of a 

preliminary four-step procedure: historical research, 

documentation, inventory, and stabilization. 

Historical Research. 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 

1 
2 

Figure 2. Early photographs discovered during historical research can be 

enhanced through photo-micrography to accurately recreate missing 

elements and details during restoration. The enlargements helped clariftj 

questions about the porch column detail and the type of shutter hardware. 

photo: E. C. Stanton House, courtesy Seneca Falls Historical Society, New York; insets: NPS North Atlantic Cultural Resource Center, Building Conservation Branch. 

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 threedimensional physical investigation go hand-in-hand in 

analyzing historic structures. The quality and success of 

any restoration project is founded upon the initial research. 

Documentation. 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. Professionals 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. 

."1',J ~..J~ 

"., ~ ift~ ~ 

o$io..d ~¥l"4 M.l1-~ .... ~ 

• I\.t.otu., 

, , 

c." 

+-

r 

Figure 3. Dating, labeling, and providing annotated photographs is a simple, yet effective, way to document today's preservation efforts for 

future work and research. A useful document can be created by mounting a photograph upon archival paper and writing the annotations by hand. photo: NPS Preservation Assistance Division Files. 

Documentation is particularly valuable when a feature will 

be removed or altered. 

Inventory. 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. 

Stabilization. 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 
Figure 4. An inventory of animal nests found within hidden spaces of a structure may yield unexpected evidence, such as informatioll about food, 

decorative arts, and cultural or social traditions of every day life. Typical 

items of paper, fabric and wood are important artifacts which are generally not found during archeology digs in the ground. photo: Tom 

Graves, Jr., courtesy Jefferson's Poplar Forest. 

Figure 5. In vestigation frequently identifies urgent needs of stabilization. 

Priority must be given to issues of safety and structural integrity. 

Supplemental support, such as temporary shoring, may be required to 

prevent collapse and should be reviewed by a structural engineer. 

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. 

Investigators and Investigative Skills 

General and Specialized Skills. 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 

Figure 6. An investigator must have the skill and ability to closely observe and analyze the materials with a broad understanding of historic construction practices and technologies. Through the collection of 

samples and analysis of materials, investigative questions are either answered, refined, or formulated. 

3 
4 

Showing the Evolution of an 

18th Century Farmhouse 

Most structures evolve over time. Houses, perhaps 

more than other building types, are often subjected 

to a full range of change that reflects a wide variety 

of solutions for creating new living space or 

eliminating outmoded spaces. Architectural changes 

to historic houses can be studied through the close 

physical examination of construction and decorative 

details. Tracing the history of alterations over time 

is tantamount to "excavating" the structure, 

somewhat like an archeological investigation. By 

peeling back its layers of occupation and assembling 

plan changes, a sequence of consecutive solutions or 

transformations can be developed that reveals 

people's ongoing desires for new and improved 

living conditions. 

The example of a Sussex County, Delaware, house--

from ca. 1790 to the early 1900s--illustrates how 

complicated the pattern of change over time can 

become in outlining an individual house history. 

The Hunter Farm House was built in the 18th 

century as a double-cell, double-pile, half-passage 

plan (a). Two bays across the front and two stories 

tall, the house possessed back-to-back corner 

fireplaces with fully paneled fireplace walls in the 

front and back rooms. A stair in the rear passage 

provided access to the second floor. A one-story, 

two-room shed that was attached to the gable wall 

farthest from the fireplace was accessed by a low 

door leading from the front room. 

During the course of its history, the house was 

altered at least three times. The five-part illustration 

shows the house's transformation from an open plan 

to a Georgian plan and the subsequent addition and 

re-arrangement of service rooms for cooking and 

storage. The first remodelling occurred in the early 

nineteenth century when the lean-to shed was 

removed, and a two-story, single-pile, two-bay 

house was moved up and attached to the northwest 

gable of the existing building (b). (The newly 

attached building had originally been furnished 

with opposing doors and windows on the front and 

back facades, a fireplace on the southeast gable, and 

double windows on the opposite end.) When the 

second building was joined to the first, the fireplace 

in the newer building was relocated to the opposite 

gable; the front door in the older house moved to a 

more central position; and a center-hall plan created 

with a roughly symmetrical front elevation (c). A 

subsequent alteration later in the nineteenth century 

included the addition of a one-story rear service ell 

(d). Finally, in the early 1900s, the one-story service 

wing was increased. During this last remodeling, the 

large kitchen hearth was demolished and replaced 

with a stove and new brick flue (e). 

Sidebar: Bernard L. Herman and Gabrielle M. Lanier, 

University of Delaware. Drawings by: Center for Historic 

Architecture and Engineering, University of Delaware. 

(A) CIRCA 1760 

(8) 

(C) CIRCA 1800 

(D) CIRCA 1850 

PERIOD I 

PERIOD II 

PERIOD III 

PERIOD IV 

r-

-f1.., 

") 
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. 

Specialists on a Team. 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 

craftsman, an architect or a conservator. For large-scale 

projects, a team approach may need to be adopted, 

consisting of professionals interacting with additional 

consultants. Consulting specialists may include 

architectural historians, architectural conservators, 

craftsmen, 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 

surveyor 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 

itself. 

Architectural Evidence: Studying the Fabric 

of the Historic Building: 

Original Construction and Later Changes. 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 innovationsas 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. 

Conducting the Architectural Investigation 

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 nondestructive testing, and various degrees of sub-surface 

destructive testing. 

.... 

+l===t=;;;:;;;;;;;;-t:==:::;:r 1.- .., ~ I 

~I WI 

I 

I 

I 

I 

_-1 I _________ _ 

Figure 8. During the initial visit, the architectural investigator may be able to resolve many questions about the building's condition and chronology while recording their observations through field notes and annotated sketches. Drawing by Marianne Graham, courtesy Jefferson's Poplar Forest Restoration Field School. 

5 
6 

Looking More Closely at Historic Building 

Materials and Features 

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. 

Figure A. Careful examination of the masonry reveals different periods of 

construction and repair through the composition and detailing of bricks 

and mortar. Depending upon location, open vertical joints may indicate 

the location of nailing blocks for decorative trim or weeps for drainage. 

These open joints at the building's cornice show evidence of an earlier 

wooden entablature extending down two courses below the present trim. 

The paint ghosts below the lowest blocks confirms the entablature's 

existence and provides clues to its size and finish. 

Masonry. 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. 

Figure B. Without damaging or altering historic fabric, X-ray images of 

wood connections provide internal views of construction materials and 

techniques. These x-ray images show nails being used to form the 

connections of a door opening in a wood stud wall covered with plaster 

and cut wooden lath. A single technician can operate the portable 

equipment and develop the film on site for immediate analysis. photos: 

NPS North Atlantic Cultural Resource Center, Building Conservation 

Branch. 

Wood. 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 re-used or re-cycled? Re-used 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. 

Figure C. In many cases, new materials or coverings are placed directly over existing exterior features, preserving the original materials 

underneath. Here, the removal of a modern shingle roof and its 

underlayment revealed an historic standing seam metal roof. photo: courtesy, Phillips and Opperman, P.A. 

Roofs. 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, nineteenthcentury 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 midnineteenth century, and into the twentieth, the range and 

choice of roof coverings greatly expanded. 

Floors. 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. 

Figure D. Building styles change over time as moldings and trims are added and removed. The ghosts of the previous woodwork are often left 

behind and preserved under the new trim. This photograph shows 

distinct profiles of architectural trim from three successive periods. 

photo: courtesy, Valentine Museum, Richmond, Virginia . 

Walls. 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, 

en tablatures, cornices, mantels and shelves? Ghosts can be 

formed by paint, plaster, stucco, wear, weathering or dirt. 

Interior walls from the eighteenth and early nineteenthcentury 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 

7 
8 

the installation of re-used 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 re-use 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. 

Figure E. Discarded items are routinely stored within attics, then 

forgotten, only to be discovered during a later investigation. Seemingly 

worthless clutter and debris may help answer many questions. A 

thorough inventory should be performed before evaluating any object's 

usefulness. 

Attics and Basements. 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 the 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 eras. 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. 

Figure F. Outdated fixtures and systems are frequently abandoned in 

place when more modern units are installed. Examining and 

documenting their existence can provide a technological reference to 

the history and use of many rooms or structures. photo: NPS 

Preservation Assistance Division Files. 

Mechanical, Electrical, Plumbing and Other Systems. 

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. 
~._.- -.---.---.-.-----~- t @-----------1, ;,&-----0 @i~ ::-------~ ~ -:..~\ ~.::.-----_--::::.::.::_: I I 

" II: @ A 

: ~ __ -I---'L.>~ 

I , -----------,- -- \1 I ... --------.. -----

, I 

:: 0 

~~-~-:..~!~=~ -~, ------t--liHlf ~f ~£Jl ~ J t1.r<~EI.o tJE.I4~r G-f ! 0 t>f ~~W'Pf. 

;, ~:-,~--------,---- I ------------

Figure 9. Raking light is used to show irregularities on flat surfaces. Patches, repairs, and alterations can then be mapped by the shadows or ghosts they cast. In this case, the pattern of patched plaster suggested the removal shelves and a balustrade handrail from the wall. Historical research and plaster analysis 

confirmed the findings and the sequence of change. 

Reconnaissance. 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. 

Surface Mapping. 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. 

Non-Destructive Testing. 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 

SUPPORT 

Figure 10. Top: A boroscope is a fiber-optic tube which can provide views 

into the framing connections of a wall through an existing crack or hole. 

Bottom: Once the image is oriented, the investigator can see an open joint 

between the wood stud and its nailed lateral support. photos: NPS North 

Atlantic Cultural Resource Center, Building Conservation Branch. 

9 
10 

technology combines the boroscope with video cameras 

using fiber optic illumination. In addition to the more 

common use of infra-red photography, similar nondestructive 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. 

Destructive Testing. Most investigations require nothing 

more than historical research, surface examination and nondestructive 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 nondestructive 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 

investigation. 

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 be cyclical, like history, and 

documentation must be left for future generations, both on 

the wall and in the files. 

Laboratory Analysis. 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 

Figure 11. The physical evidence of cracks and patches seen during surface mapping suggested an abandoned fireplace. Right: Exploratory testing was used 

to verijij its location. Left: Museum restoration required more detailed probing to discover the original detailing. Plaster and brick were carefully 

documented and removed to determine the fireplace's type, size, and decoration. The rectangular slots held wooden nailing blocks supporting the mantel and surround. A indicates the inside edge of the surround; B points to the ghost from an iron firebacl< and C shows the original floor level of the hearth. 
Figure 12. During a thorough investigation, the mortar sample is viewed 

under ~ microscope using various lighting to find the presence of coatings or additIVes. It IS then ;sround and washed in an acid bath to separate 

and free the sand and fIbers. After further cleaning, these fines are stored 

and used for comparison in matching or dating repairs and alterations. photos: NPS North Atlantic Cultural Resource Center, Building 

Conservation Branch. 

sampling and microscopic laboratory work using chemical 

analysis and standardized color notations. Consultants 

without the proper kno~ledge 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 Neutron 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 through 

the use of an electron microscope. In both tests, the 

gathered information is plotted and matched with the 

reactions of·known elements. The results provide a 

quantitative and qualitative profile of the sample's 

elemental components for use in further comparisons. 

Dendrochronology presents a minimally destructive 

process for dating wooden members. Also called tree ring 

dating, this process relies on the comparative wet and dry 

growth seasons of trees as seen in their rings via a core 

sample. This technique has two limitations: a very 

extensive data base must be compiled for climatic 

conditions over a long span of years and matched with 

corresponding tree ring samples; and the core samples can 

only be taken from timber which still has a bark edge. 

Simple identification of wood species during an 

investigation can be determined from small samples sent to 

a forest products laboratory. 

After Architectural Investigation: 

Weighing the Evidence 

Evidence, questions, and hypotheses must be continually 

evaluated during investigation. Like a detective 

constructing a case, an investigator must sort out 

information to get at "the facts." Yet, are the "facts" 

conclusive at any time? 

Observations made during the surface mapping may 

identify random features. These features begin to form 

patterns; then, sets of patterns, perhaps representing 

alterations from multiple eras, begin to appear. If the right 

questions are not asked, the evidence can remain hidden. 

Hypotheses are formed, questioned, tested, re-formed and 

either rejected or substantiated. This process is repeated as 

more "facts" are uncovered and questions asked. 

Eventually the evidence seems conclusive. These 

conclusions, in turn, may lead to re-examination, more 

historical research, and the advice of specialized 

consultants. At some point, treatment generally follows 

based on the collective, educated conclusions of an entire 

professional team. 

Keeping a Responsible Record 

for Future Investigators 

The evidence collected during investigation, and any 

conclusions which can be drawn from it, should be 

documented in a written report. The complexity of a 

project dictates the complexity of the resulting record. It 

may be wise to maintain a report in an expandable format if 

long or extensive work is expected-additional evidence 

will undoubtedly need to be incorporated that alters 

previous conclusions. Reports tend to range from 

annotated photographs in loose-leaf binders to full-length 

bound "books." 

Putting findings and conclusions in an accessible form 

helps those who are planning treatment. For example, a 

rehabilitation project may require documentation to satisfy 

grant funding or tax credit program requirements; 

preservation and restoration projects always need careful 

documentation to guide the work. After work, the 

investigation report and notes on the treatment itself are 

made into a permanent file record. Whether or not work is 

11 
12 

being planned, the architectural investigation report will 

always be of value to future researchers or owners of the 

building. 

The most common professional document is called an 

Historic Structure Report. This invaluable tool for 

preservation typically contains historical as well as physical 

information. Sections include a history of the building, an 

architectural description of the original structure and 

changes made over time, the results of all investigations, a 

record of current conditions or problems, of past repairs 

and treatments, and recommendations for current and 

future action. They are seldom definitive; thus, research is a 

continuing process. 

Conclusion 

Architectural investigation plays a critical role in making 

responsible decisions about treating and interpreting 

historic buildings. A successful project to research, 

inventory, document, and ultimately treat and interpret a 

building is directly linked to the knowledge and skills of 

architectural investigators and other historic preservation 

specialists. The expressed goal of historic preservation is to 

protect and preserve materials and features that convey the 

significant history of a place. Careful architectural 

investigation-together with historical research-provides 

a firm foundation for this goal. 

Acknowledgements 

Travis C. McDonald, Jr. is an architectural historian who serves as the 

Restoration Coordinator at Thomas jefferson's Poplar Forest near Lynchburg, 

Virginia. He respectively dedicates this work to three masters of architectural 

investigation: Henry A. Judd, former Chief Historical Architect of the National 

Park Service; Lee H. Nelson, former Chief, Preservation Assistance Division NPS; 

and Paul E. Buchanan, former Director of Architectural Research at the Colonial 

Williamsburg Foundation. The author gratefully acknowledges the following 

professionals for their help in reviewing this manuscript: Edward A. Chappell, 

Colonial Williamsburg; E. Blaine Cliver, Preservation Assistance Division NPS; 

Stanley O. Graves, National Conference of State Historic Preservation Officers; 

Bernard L. Herman, University of Delaware; H. Ward Jand!, Preservation 

Assistance Division NPS; Hugh C. Miller, Virginia State Historic Preservation 

Office; Orlando Ridout V, Maryland Historical Trust; William Seale; and 

Bibliography 

Bullock, Orin M. Jr., The Restoration Manual. Norwalk, CT.: 

Silvermine Publishers, 1966. 

Burns, John A, editor. Recording Historic Structures. 

Washington, D.C.: The AlA Press, 1989. 

Howard, Hugh. How Old Is This House? New York: 

Noonday Press, 1989. 

Howe, Barbara J., Dolores A Fleming, Emory L. Kemp, and 

Ruth Ann Overbeck. Houses and Homes: Exploring Their 

History. Nashville, TN.: American Association for State and 

Local History, 1987. 

Judd, Henry A, Before Restoration Begins. Nashville, TN.: 

American Association for State and Local History, 1973. 

Kitchen, Judith L., Caring For Your Old House. Washington, 

D.C.: The Preservation Press, 1991. 

Seale, William, Recreating the Historic House Interior. 

Nashville, TN.: American Association for State and Local 

History, 1979. 

Secretary of the Interior's Standards for the Treatment of Historic 

Properties. Washington, D.C.: Preservation Assistance 

Division, National Park Service, U.S. Department of the 

Interior, 1992. 

Secretary of the Interior's Standards and Guidelines for 

Architectural and Engineering Documentation: HABS/HAER 

Standards. Washington, D.C.: HABS/HAER, National Park 

Service, U.S. Department of the Interior, 1990. 

Cover Photo: 

An historical architect analyzes and records his investigative findings 

while on site. photo: courtesy Valentine Museum. 

professional staff members of the National Park Service. Timothy A. Buehner 

served as project coordinator and Kay D. Weeks as project editor. 

All photographs are by the Author unless otherwise noted. 

This publication has been prepared pursuant to the National Historic 

Preservation Act of 1966, as amended, which directs the Secretary of the Interior 

to develop and make available information concerning historic properties. 

Comments on the usefulness of this publication may be directed to: Preservation 

Assistance Division, National Park Service, P.O. Box 37127, Washington, D.C. 

20013-7127. This publication is not copyrighted and can be reproduced without 

penalty. Normal procedures for credit to the authors and the National Park 

Service are appreciated. 

ISSN: 0885-7017.