41 PRESERVATION 

BRIEFS 

The Seismic Retrofit of Historic Buildings: 

Keeping Preservation in the Forefront 

David W. Look, AlA, Terry Wong, PE, 

and Sylvia Rose Augustus 

G -::.~ u.s. Department of the Interior .' . .:. if. National Park Service 

. . "._.. Cultural Resources 

.- Heritage Preservation Services 

Violent, swift, and unpredictable, earthquakes result from 

sudden movements of the geological plates that form the 

earth's crust, generally along cracks or fractures known as 

"faults." If a building has not been designed and 

constructed to absorb these swaying ground motions, then 

major structural damage, or outright collapse, can result, 

with grave risk to human life. Historic buildings are 

especially vulnerable in this regard. As a result, more and 

more communities are beginning to adopt stringent 

requirements for seismic retrofit of existing buildings. And 

despite popular misconceptions, the risks of earthquakes are 

not limited to the West Coast, as the Seismic Zone Map on 

page 14 illustrates. 

Although historic and other older buildings can be retrofitted to survive earthquakes, many retrofit practices damage 

or destroy the very features that make such buildings 

significant. Life-safety issues are foremost and, fortunately, 

there are various approaches which can save historic 

buildings both from the devastation caused by earthquakes 

and from the damage inflicted by well-intentioned but 

insensitive retrofit procedures. Building owners, managers, 

consultants, and communities need to be actively involved 

in preparing documents and readying irreplaceable historic 

resources from these damages (see illus.l). 

This Preservation Brief provides essential information on 

how earthquakes affect historic buildings, how a historic 

preservation ethic can guide responsible decisions, and how 

various methods of seismic retrofit can protect human lives 

and historic structures. Because many of the terms used in 

this Brief are technical, a glossary is provided on page 7. 

The Brief focuses on unreinforced masonry buildings 

because these are the most vulnerable of our older resources, 

but the guidance is appropriate for all historic buildings. 

Damage to non-structural elements such as furnishings and 

collections is beyond the scope of this Brief, but consideration should be given to securing and protecting these 

cultural resources as well. 

Planning the retrofit of historic buildings before an earthquake strikes is a process that requires teamwork on the part 

of engineers, architects, code officials, and agency administrators. Accordingly, this Brief also presents guidance on 

assembling a professional team and ensuring its successful 

interaction. Project personnel working together can ensure 

that the architectural, engineering, financial, cultural, and 

social values of historic buildings are preserved, while 

rendering them safe for continued use. 

1. Earthquake damage to historic buildings can be repaired in a manner sensitive to their historic character as seen in this ca. 1928 five story apartment 

building. The owners used a combination of federa l rehabilitation tax credits, community development block grants, and post earthquake grants to fund a portion of the rehabilitation and seismic upgrade costs. Photos: Historic Resources Group, Los Angeles. 
2 

Balancing Seismic Retrofit and Preservation 

Reinforcing a historic building to meet new construction 

requirements, as prescribed by many building codes, can 

destroy much of a historic building's appearance and 

integrity. This is because the most expedient ways to 

reinforce a building according to such codes are to impose 

structural members and to fill irregularities or large 

openings, regardless of the placement of architectural 

detail. The results can be quite intrusive (see illus. 2). 

However, structural reinforcement can be introduced 

sensitively. In such cases, its deSign, placement, patterning, 

and detailing respect the historic character of the building, 

even when the reinforcement itself is visible. 

Three important preservation principles should be kept in 

mind when undertaking seismic retrofit projects: 

• Historic materials should be preserved and retained to the 

greatest extent possible and not replaced wholesale in the 

process of seismic strengthening; 

• New seismic retrofit systems, whether hidden or exposed, 

should respect the character and integrity of the historic 

building and be visually compatible with it in design; 

and, 

• Seismic work should be "reversible" to the greatest extent 

possible to allow removal for future use of improved 

systems and traditional repair of remaining historic 

materials. 

It is strongly advised that all owners of historically 

significant buildings contemplating seismic retrofit become 

familiar with The Secretary of the Interior's Standards for the 

Treatment of Historic Properties, which are published by the 

National Park Service and cited in the bibliography of this 

publication. These standards identify approaches for 

working with historic buildings, including preservation, 

rehabilitation, and restoration. Code-required work to 

make buildings functional and safe is an integral 

component of each approach identified in the Standards. 

While some seismic upgrading work is more permanent 

than reversible, care must be taken to preserve historic 

materials to the greatest extent possible and for new work 

to have a minimal visual impact on the historic appearance 

of the building. 

2. Standard approaches to seismic retrofit, as seen with the diagonally 

braced frame crossing in front of the historic windows. are visually 

intrusive. Solutions, such as using hidden moment frames around the perimeter of the window, will meet the goals of historic preservation and 

seismic retrofit. Photo: Steade Craigo. 

Earthquake Damage 

to Historic Buildings: 

Assessing Principal 

Risk Factors 

Typical earthquake damage 

to most older and historic 

buildings results from poor 

ductility-or flexibility-of 

the building and, 

specifically, poor structural 

connections between walls, 

floors, and foundations 

combined with the very 

heavy weight and mass of 

historic materials that are 

moved by seismic forces 

and must be resisted. In 

buildings that have not 

been seismically upgraded, 

particularly unreinforced 

masonry buildings, 

parapets, chimneys, and 

gable ends may dislodge 

and fall to the ground 

during a moderate to severe 

earthquake (see illus. 3). 

Walls, floors, roofs, 

skylights, porches, and 

stairs which rely on tied 

connections may simply 

fail. Interior structural 

supports may partially or 

totally collapse. 

Unreinforced masonry 

walls between openings 

often exhibit shear (or 

diagonal) cracking. Upper 

stories may collapse onto 

under-reinforced lower 

floors with large perimeter 

openings or atriums. 

Unbraced infill material 

between structural or rigid 

frame supports may 

dislodge. Adjacent 

buildings with separate 

foundations may move 

differently in an earthquake 

crea ting damage between 

them. Poorly anchored 

wood frame buildings tend 

to slide off their 

foundations. Ruptured gas 

and water lines often cause 

fire and water damage. 

Many of these 

vulnerabilities can be 

mitigated by understanding 

how the forces unleashed 

in an earthquake affect the 

building, then planning 

and implementing 

appropriate remedial 

treatments. 

fl:~l?I ' ··J't'1 

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'~h-zJ.#" :-" r1 < .it ... ' r~-=-

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3. Forces from moderate to serious 

=-

earthquakes ca used a) the untied gable to fail, b) the first floor to collapse c) 

cracks from the pounding effect of 

adjacent buildings, and d) and diagonal 

cracks in exterior masonnj between 

windows to form. Photos: David Look. 
Six principal factors influence how and why historic 

buildings are damaged in an earthquake: (1) depth of the 

earthquake and subsequent strength of earthquake waves 

reaching the surface; (2) duration of the earthquake, 

including after-shock tremors; (3) proximity of the building 

to the earthquake epicenter, although distance is not 

necessarily a direct relationship; (4) geological and soil 

conditions; (5) building construction details, including 

materials, structural systems, and plan configuration; and 

(6) existing building condition, including maintenance 

level. 

The first three factors-the depth, duration, and proximity 

to the fault-are beyond human control. Recent 

earthquakes have shown the fourth factor, geological soil 

conditions, to be as important as any of the other factors 

because loose, soft soils tend to amplify ground motion, 

thereby increasing damage. Further, there is the tendency 

of soft, unstable soils to "liquefy" as the ground vibrates, 

causing the building foundations to sink unevenly. This 

fourth factor, geological and soil conditions, is difficult to 

address in a retrofit situation, although it can be planned for 

in new construction. The last two factors-the building'S 

construction type and its existing physical condition-are 

the two factors over which building owners and managers 

have control and can ultimately affect how the historic 

property performs in an earthquake (see illus. 4). 

4. The compact size and good condition of the masonry building on the 

left withstood the earthquake except for the loss of the unsupported 

chimney at the roof line. The brick building on the right appears to have 

sustained more damage. Photo: Steade Craigo. 

Although historic buildings present problems, the way they 

were constructed often has intrinsic benefits that should not 

be overlooked. Diagonal subflooring under tongue-andgroove nailed flooring can provide a diaphragm, or 

horizontal membrane, that ties the building together. 

Interior masonry walls employing wire lath with plaster 

also add strength that binds materials together. The typical 

construction of older buildings with partition walls that 

extend from floor to ceiling (instead of just to the underside 

of a dropped ceiling) also provides additional support and 

load transfer during an earthquake that keeps shifting 

floors from collapsing. Moreover, buildings constructed of 

unrein forced masonry with a wall thickness to height ratio 

that does not exceed code requirements can often survive 

shaking without serious damage. The stability of 

unrein forced masonry walls should not be underestimated; 

while the masonry may crack, it often does not shift out of 

plumb enough to collapse. 

Type of Building and Construction 

A historic building's construction and materials determine 

its behavior during an earthquake. Some buildings, such as 

wooden frame structures, are quite ductile and, thus, able to 

absorb substantial movements. Others, such as unreinforced brick or adobe buildings comprised of heavy individual 

load-bearing units, are more susceptible to damage from 

shaking. If an earthquake is strong, or continues for a long 

time, building elements that are poorly attached or unreinforced may collapse. Most historic buildings still standing 

in earthquake zones have survived some shaking, but may 

be structurally weakened. 

Buildings of more rigid construction techniques may also 

have seismic deficiencies. Masonry infill-wall buildings are 

generally built of steel or concrete structural frames with 

unreinforced masonry sections or panels set within the 

frame. While the structural frames may survive an earthquake, the masonry infill can crack and, in some cases, 

dislodge. The reaction of concrete buildings and concrete 

frame structures is largely dependent upon the extent and 

configuration of iron or steel reinforcement. Early 

buildings constructed of concrete are often inadequately 

reinforced, inadequately tied, or both, and are thus 

susceptible to damage during earthquakes. 

Recognition of the configuration of the historic structure 

and inherent areas of weakness are essential to addressing 

appropriate alternatives for seismic retrofit. For example, 

the plan and elevation may be as important as building 

materials and structural systems in determining a historic 

building's survival in an earthquake. Small round, square, 

or rectangular buildings generally survive an earthquake 

because their geometry allows for equal resistance of lateral 

forces in all directions. The more complex and irregular the 

plan, however, the more likely the building will be 

damaged during an earthquake because of its uneven 

strength and stiffness in different directions. Structures 

having an "L," "T," "H," "U," or "E" shape have unequal 

resistance, with the stress concentrated at corners and 

intersections. This is of particular concern if the buildings 

have flexible structural systems and/ or an irregular layout 

of shear walls which may cause portions of the building to 

pull apart. 

Similarly, the more complex and irregular a building 

elevation, the more susceptible it is to damage, especially in 

tall structures. Large or multiple openings around the 

building on the ground level, such as storefronts or garage 

openings, or floors with columns and walls running in only 

one direction are commonly known as "soft stories" and are 

prone to structural damage. 

Building Condition 

Much of the damage that occurs during an earthquake is 

directly related to the building's existing condition and 

maintenance history. Well maintained buildings, even 

without added reinforcement, survive better than buildings 

weakened by lack of maintenance. The capacity of the 

structural system to resist earthquakes may be severely 

reduced if previous alterations or earthquakes have 

weakened structural connections or if materials have 

deteriorated from moisture, termite, or other damage. 

Furthermore, in unreinforced historic masonry buildings, 

deteriorated mortar joints can weaken entire walls. Cyclical 

maintenance, which reduces moisture penetration and 

,1 
4 

erosion of materials, is therefore essential. Because damage 

can be cumulative, it is important to analyze the structural 

capacity of the building. 

Over time, structural members can become loose and pose 

a major liability. Unrein forced historic masonry buildings 

typically have a friction-fit connection between horizontal 

and vertical structural members, and the shaking caused by 

an earthquake pulls them apart. With insufficient bearing 

surface for beams, joists, and rafters against the load 

bearing walls or support columns, they fail. The resulting 

structural inadequacy may cause a partial or complete 

building collapse, depending on the severity of the 

earthquake and the internal wall configuration. Tying the 

building together by making a positive anchored or braced 

connection between walls, columns, and framing members, 

is key to the seismic retrofit of historic buildings. 

Putting a Team Together 

The two goals of the seismic retrofit in historic buildings 

are life safety and the protection of older and historic 

buildings during and after an earthquake. Because 

rehabilitation should be sensitive to historic materials and 

the building's historic character, it is important to put 

together a team experienced in both seismic requirements 

and historic preservation. Team members should be 

selected for their experience with similar projects, and may 

include architects, engineers, code specialists, contractors, 

and preservation consultants. Because the typical seismic 

codes are written for new construction, it is important that 

both the architect and structural engineer be knowledgeable about historic buildings and about meeting building 

code equivalencies and using alternative solutions. Local 

and state building officials can identify regulatory 

requirements, alternative approaches to meeting these 

requirements, and if the jurisdiction uses a historic 

preservation or building conservation code. Even on small 

projects that cannot support a full professional team, 

consultants should be familiar with historic preservation 

goals. The State Historic Preservation Office and the local 

historic preservation office or commission may be able to 

identify consultants who have been successful in 

preserving historic buildings during seismic retrofit work. 

Once the team has been assembled, their tasks include: 

Compiling documentation. The team should review all 

available documentation on the historic building, including 

any previous documentation assembled to nominate the 

structure to the National Register of Historic Places, and 

any previous Historic Structures Reports. Original plans 

and specifications as well as those showing alterations 

through time often detail structural connections. Early real 

estate or insurance plans, such as the Sanborn Maps, note 

changes over time. Historic photographs of the building 

under construction or before and after previous 

earthquakes are invaluable. Base maps for geological or 

seismic studies and utility maps showing the location of 

water, gas, and electric lines should be also identified. The 

municipal or state office of emergency preparedness can 

provide data on earthquake hazard plans for the 

community. 

Evaluating significant features and spaces. The team must also 

identify areas of a historic building and its site that exhibit 

design integrity or historical significance which must be 

preserved. It is critical, and a great challenge, to protect 

these major features, such as domes, atriums, and vaulted 

spaces or highly decorative elements, such as mosaics, 

murals, and frescoes. In some cases, secondary areas of the 

building can provide spaces for additional reinforcement 

behind these major features, thus saving them from damage 

during seismic retrofit work. Both primary and secondary 

spaces, features, and finishes should, thus, be identified. 

Assessing the condition of the building and the risk hazards. The 

team then assesses the general physical condition of the 

building's interior and exterior, and identifies areas 

vulnerable to seismic damage. This often requires a 

structural engineer or testing firm to determine the strength 

and durability of materials and connections (see illus. 5). A 

sliding scale of potential damage is established, based on 

the probability of hazard by locale and building use. This 

helps the owner distinguish between areas in which 

repairable damage, such as cracking, may occur and those 

in which life-threatening problems may arise. These 

findings help guide cost-benefit decisions, especially when 

budgets are limited. 

5. A careful program of in-place testing is essential to evaluate the existing seismic capacity of a building. This masonry pushtest uses hydraulic jacks to estimate the shear capacity of 

the wall. Test locations should 

be in areas that do not destroy significant features and repairs should be carried out carefully. 

Photo: Architectural Resources Group, San Francisco. 

Evaluating local and state 

codes and requirements. Few 

codes consider historic 

buildings, but the California 

State Historical Code and 

the Uniform Code for 

Building Conservation 

provide excellent models for jurisdictions to adopt. Code 

officials should always be asked where alternative 

approaches can be taken to provide life safety if the specified 

requirements of a code would destroy significant historic 

materials and features. Some jurisdictions require the 

removal of parapets, chimneys, or projecting decoration from 

unreinforced masonry buildings which is not a preservation 

approach. Professionals on the team should be prepared 

with alternatives that allow for mitigating potential damage 

to such features while retaining them through reattachment 

or strengthening. 

Developing a retrofit plan. The final task of the project team is 

to develop a retrofit plan. The plan may require multiple 

treatments, each more comprehensive than the last. Treating 

life-safety issues as well as providing a safe route of exit 

should be evaluated for all buildings. Developing more 

comprehensive plans, often combined with future rehabilitation, is reasonable. Long-term restoration solutions phased 

in over time as funding is available should also be considered. In every case, owners and their planning teams should 

consider options that keep preservation goals in mind. 

There are significant advantages of completing a seismic 

survey and analysis even if resources for implementing a 
retrofit are not yet available. Once the retrofit plan is 

finished, the project team will have a document by which to 

assess future damage and proceed with emergency repairs. 

If construction is phased, its impact to the whole building 

should be understood. Some partially completed retrofit 

measures have left buildings more rigid in one area than in 

others, thereby contributing to more extensive damage 

during an ensuing earthquake. 

Planning for Seismic Retrofit: How Much 

and Where? 

The integrity and significance of the historic building, 

paired with the cost and benefit of seismic upgrading, need 

to be weighed by the owner and the consulting team. 

Buildings in less active seismic areas may need little or no 

further bracing or tying. Buildings in more active seismic 

zones, however, may need more extensive intervention. 

Options for the level of seismic retrofit generally fall into 

four classifications, depending on the expected seismic 

activity and the desired level of performance. Realistically, 

for historic buildings, only the first three categories apply. 

1) Basic Life Safety. This addresses the most serious lifesafety concerns by correcting those deficiencies that 

could lead to serious human injury or total building 

collapse. Upgrades may include bracing and tying the 

most vulnerable elements of the building, such as 

parapets, chimneys, and projecting ornamentation or 

reinforcing routes of exit. (see illus. 6). It is expected that 

if an earthquake were to occur, the building would not 

collapse but would be seriously damaged requiring 

major repairs. 

2) Enhanced Life Safety. In this approach, the building is 

upgraded using a flexible approach to the building codes 

for moderate earthquakes. Inherent deficiencies found in 

older buildings, such as poor floor to wall framing 

connections and unbraced masonry walls would be 

corrected (see illus. 7). After a design level earthquake, 

some structural damage is anticipated, such as masonry 

cracking, and the building would be temporarily 

unusable. 

Sheathing Cripple Walls 

Wall Detail 

MATERIALS NEEDED TOOLS NEEDED 

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Simp$Ofl A,35 (nming clips .. -ilh Fr.ming square 

N8 nails Of't:qllivaient Anchorboltl 

Plywood blade 

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6. Often simple approaches, such as nailing plywood stiffeners between 

crawlspace studs and onto floor joist above and bolting sill plates to 

foundations can make a dramatic difference in protecting a building from 

seismic damage. Illustration: Reproduced with permission from Home 

Earthquake Preparedness Guide. EQE Incorporated, San Francisco, CA. 

7. More exte/1sive seismic issues can be addressed through structural 

reinforcement, the most common methods using anchor ties and braces. 

Shown here is an interior diagonal frame, to be covered, which will 

dampen and transfer seismic loads in a designed path from foundation to 

roof. Photo: David Look. 

8. Full seismic restructuring to ensure that buildings survive a major 

earthquake with a minimum of damage may involve extensive 

reinforcement. Upon completion, the changes to this ca. 1932 Gothic 

Revival building to add base isolation at the foundation were not visually 

apparent. Photo: © Jonathan Farrer, courtesy University of California at 

Los Angeles (UCLA), Capital Programs. 

3) Enhanced Damage Control. Historic buildings are 

substantially rehabilitated to meet, to the extent possible, 

the prescribed building code provision (See illus. 8). 

Some minor repairable damage would be expected after 

a major earthquake. 

4) Immediate Occupancy. This approach is intended for 

designated hospitals and emergency preparedness 

centers remaining open and operational after a major 

earthquake. Even most modern buildings do not meet 

this level of construction, and so for a historic building to 

meet this requirement, it would have to be almost totally 

reconstructed of new materials which, philosophically, 

does not reflect preservation criteria. 

5 
6 

Devising the most appropriate approach for a 

particular historic building will depend on a 

variety of factors, including the building's use, 

whether it remains occupied during 

construction, applicable codes, budgetary 

constraints, and projected risk of damage. 

From a design perspective, the vast majority of 

historic buildings can tolerate a well-planned 

hidden system of reinforcement. Utilitarian 

structures, such as warehouses, may be able to 

receive fairly visible reinforcement systems 

without undue damage to their historic 

character. Other more architecturally detailed 

buildings or those with more finished interior 

surfaces, however, will benefit from more 

hidden systems; installation of such systems 

may even require the temporary removal of 

significant features to assure their protection. 

Most buildings, particularly commercial 

rehabilitations, can incorporate seismic 

strengthening during other construction work 

in a way that ensures a high degree of 

retention of historic materials in place. 

9. These stlldies for a public building compared, in the shaded areas, the amount of historic 

material that wOllld be affected by (a) the Uniform Building Code requirements, (b) engineering 

alternatives that protected significallt historic materials, and (c) the lise of base isolation systems. 

The cost for implementing the 3 proposals was similar, and while proposal (c) was selected there 

were mallY positive aspects to both (b) and (c). Photos: George Siekkinen, with permission from 

Ehrenkrantz, Eckstut, & Kuhn Architects. 

Assessing the Cost of Seismic Retrofit 

Cost plays a critical role in selecting the most appropriate 

retrofit measure. It is always best to undertake retrofit 

measures before an earthquake occurs, when options are 

available for strengthening existing members. Once 

damage is done, the cost will be substantially higher and 

finding engineers, architects, and contractors available to do 

the work on a constricted schedule will be more difficult. 

Planned seismic retrofit work may add between $10 and 

$100 per square foot to the cost of rehabilitation work 

depending on the level of intervention, the condition of the 

building, and whether work will be undertaken while the 

building is occupied. Costs can exceed several hundred 

dollars a square foot for combined restoration and seismic 

upgrade costs in major public buildings, in order to provide 

a level of structural reinforcement that would require only 

minor repairs after a major earthquake. But maintenance 

and incremental improv:ements to eliminate life-safety risks 

are within the cost realm of responsible upkeep. 

Each property owner has to weigh the costs and benefits of 

undertaking seismic retrofit in a timely manner. Owners 

may find that an extended engineering study evaluating a 

wide range of options is worthwhile. Not only can such a 

study consider the most sensitive historic preservation 

solution, but the most cost-effective one as well. In many 

cases, actual retrofit expenses have been lower than 

anticipated because a careful analysis of the existing 

building was made that took the durability and 

performance of existing historic materials into 

consideration. Most seismic retrofit is done incrementally 

or incorporated into other rehabilitation work. In large 

public buildings, seemingly expensive "high-tech" solution 

such as installing foundation base isolators can turn out to 

be justified because significant historic materials do not 

have to be removed, replaced, or replicated (see illus. 9). 

The cost for a fully retrofitted building can offset the potentialloss of income, relocation, and rebuilding after an earthquake. Without careful study, these solutions often are not 

evaluated. 

Some municipalities and states provide low-interest loans, 

tax relief, municipal bonds, or funding grants targeted to 

seismic retrofit. Federal tax incentives for the rehabilitation 

of income-producing historic buildings include seismic 

strengthening as an allowable expense. Information on 

these incentives is available from the State Historic Preservation Office. It is also in the best interest of business 

communities to support the retrofit of buildings in 

seismically active areas to reduce the loss of sales and 

property taxes, should an earthquake occur. 

Seismic Strengthening Approaches 

Seismic strength within buildings is achieved through the 

reinforcement of structural elements. Such reinforcement 

can include anchored ties, reinforced mortar joints, braced 

frames, bond beams, moment-resisting frames, shear walls, 

and horizontal diaphragms. Most historic buildings can use 

these standard, traditional methods of strengthening 

successfully, if properly designed to conform to the historic 

character of the building. In addition, there are new 

technologies and better designs for traditional connection 

devices as well as a greater acceptance of alternative 

approaches to meeting seismic requirements. While some 

technologies may still be new for retrofit, the key preservation principles on page 2 should be applied, to ensure that 

historic buildings will not be damaged by them. For an 

illustrated design guideline for using some of the more 

traditional methods on the exteriors of historic unreinforced masonry buildings, see illustration 10 on pages 8-9. 

There are varying levels of intervention for seismically 

retrofitting historic buildings based on the owner's 

program, the recommendations of the team, applicable 

codes, and the availability of funds. The approaches to 

strengthening buildings beginning on page 10 are to show a 

range of treatments and are not intended to cover all 

methods. Each building should be evaluated by qualified 

professionals prior to initiating any work. 
Maintenance/Preparedness 

Adequate maintenance ensures that existing historic 

materials remain in good condition and are not weakened by 

rot, rust, decay or other moisture problems. Without 

exception, historic buildings should be well maintained and 

an evacuation plan developed. Expectation that an earthquake will occur sometime in the future should prepare the 

owner to have emergency information and supplies on hand. 

• Check roofs, gutters, and foundations for moisture 

problems, and for corrosion of metal ties for 

parapets and chimneys. Make repairs and keep 

metal painted and in good condition. 

• Inspect and keep termite and wood boring insects 

away from wooden structural members. Check 

exit steps and porches to ensure that they are 

tightly connected and will not collapse during an 

emergency exit. 

• Check masonry for deteriorating mortar, and 

never defer repairs. Repoint, matching the historic 

mortar in composition and detailing. 

• Contact utility companies for information on flexible connectors for gas and water lines, and earthquake activated gas shut-off valves. Strap oil tanks 

down and anchor water heaters to wall framing. 

• Collect local emergency material for reference and 

implement simple household or office mitigation 

measures, such as installing latches to keep 

cabinets from flying open or braces to attach tall 

bookcases to walls. Keep drinking water, 

tarpaulins, and other emergency supplies on hand. 

Basic/Traditional Measures 

This is not an exhaustive list, but illustrates that most 

measures to reduce life-safety risks rely on using 

mechanical fasteners to tie a building together. 

Incorpora ting these measures can be done incrementally 

without waiting for extensive rehabilitation (see illus.ll12). An architectural or engineering survey should identify 

what is needed. Care should be taken to integrate these 

changes with the visual appearance of the building. 

11. Limited interventiol7 should correct obvious structural deficiencies, 

such as tying vllinerable elemel7ts together and repoil7til7g masonn;. 

Seen here is 1) anchored baIt, 2) metal joist strap, al7d 3) repainting and 

reinforcing masonry joints. UpOI7 replastering alld painting these 

reinforcements willllot be visible. Photo: Historic Preservation Partl7ers 

for Earthquake Response. 

GLOSSARY: 

Anchor Ties or bolts: Generally threaded rods or bolt 

which connect walls to floor and roof framing. Washers, 

plates, or rosettes anchor the bolt in place. 

Base isolation: the ability to isolate the structures from 

the damaging effects of earthquakes by providing a 

flexible layer between the foundations and vertical 

supports. 

Diagonal Braces: the use of diagonal, chevron or other 

type of bracing (X or K) to provide lateral resistance to 

adjacent walls. 

Core drilling: a type of vertical reinforcement of 

masonry walls that relies on drilling a continuous 

vertical core that is filled with steel reinforcing rods and 

grouting to resist in-plane shear and out-of-plane 

bending. 

Cripple wall: A frame wall between a building'S first 

floor and foundation. 

Diaphragm: A floor, roof, or continuous membrane that 

provides for the transfer of earthquake loading to the 

exterior or interior shear walls of the structure. 

Fiber wrap reinforcement: A synthetic compound of 

filaments that increase the shear capacity of structural 

members. 

Grouted bolts: anchor bolts set, generally on an angle, in 

a concrete grout mixture, avoid the problem of using an 

exposed washer. Requires a greater diameter hole than 

an anchor bolt with washer. 

Lateral forces: Generally the horizontal forces 

transferred to the building from the dynamic effects of 

wind or seismic forces. 

Life-safety: providing a level of assurance that risk of 

loss of life is kept to minimal levels. For buildings, this 

includes strengthening to reduce l)structural collapse, 2) 

falling debris, 3)blocking exits or emergency routes, and 

4) prevention of consequential fire. 

Moment-resisting frame: A steel frame designed to 

provide in-plane resistance to lateral loads particularly 

by reinforcing the joint connection between column and 

beams without adding a diagonal brace. Often used as a 

perimeter frame around storefronts or large door and 

window openings. 

Seismic retrofit: All measures that improve the 

earthquake performance of a building especially those 

that affect structural stability and reduce the potential 

for heavy structural damage or collapse. 

Shear stress: A concept in physics where forces act on a 

body in opposite directions, but not in the same line. 

Horizontal forces applied to a wall that is insufficient to 

move with these forces will crack, often in a diagonal or 

X pattern. Connections at beams and walls will also 

crack from shear stress. 

Shear wall: A wall deliberately designed to transfer the 

building's loads from the roof and floors to the 

foundation thereby preventing a building from collapse 

from wind or earthquake forces. 

Unreinforced Masonry (URM): This designation refers 

to traditional brick, block, and adobe construction that 

relies on the weight of the masonry ':lnd the bonding 

capacity of mortar to provide structwal stability. 

7 
8 

Anchor Bolts: 

Typically 1/2" bolts with flat metal 

washers (sometimes called plates or 

rosettes) are probably the most common 

retrofit procedure. The tie the exterior 

wall to the floors and roof causing the 

building to move as a single unit. 

The washers are the most noticeable part 

of the system. Anchor bolt locations are 

determined by the structural engineer. 

Decorative washers, such as cast iron 

stars, carefully placed, can enhance the 

building. Poorly placed or carelessly 

aligned washers are very noticeable. 

KEEPING PRESERVAT 

Recommended Not Recommended 

It is important to control rust by painting 

ferrous metal washers. New washers can 

be specified as stainless or galvanized 

steel. In circumstances where washers 

are visibly intrusive, the preferable 

solution would be to recess them below 

the face material. This is particularly 

applicable to stucco buildings. 

• Use decorative washers in areas with high visibility. • Align washers to create orderly appearance. 

• The anchor bolts on this building were placed in a haphazard fashion. More care should be taken to align the anchor bolt washers. Also, painting 

the washers can reduce the unsightly rust streaks 

that result from weathering. 

• Use stainless or galvanized steel and paint when 

appropriate, to prevent rust streaks. • Attempt to conceal the bolts and washers below the 

exterior finish, when appropriate. • Do not place anchor bolts at locations with high 

relief ornamentation. 

Infill Windows: 

From an architectural standpoint, infill of 

openings is not a desirable remedy and 

should be used only as a last resort. It is 

often possible to use a braced frames 

instead of infilling openings, but it may 

be more expensive. 

Recommended Not Recommended 

The purpose of filling the openings is to 

increase the shear capacity and reduce the 

stresses on the unreinforced masonry wall. 

It is not adequate to just infill with the 

same unreinforced masonry, but generally 

a reinforced concrete, reinforced block or 

reinforced brick is specified. If infilling 

the openings appears to be the only realistic method, the design solution should be 

sensitive, and if possible, limited to 

secondary elevations. The opening should 

be set back and the facing material should 

be compatible with the surrounding 

material. 

·lnfill of windows should be avoided in all cases. .Infill techniques such as this are not encouraged. 

Where absolutely required, however, the 

appearance of a window opening should be retained to suggest the original visual rhythm of the facade. 

Suggestion of a former window opening should 

have been emphasized by slightly recessing the 

former opening. 

Questions to Ask When Planning Seismic Retrofit: 

These questions should be asked with the assistance of the team to 

determine acceptable alternatives. Since there is never a single 

right answer, the design team and code officials should work 

together to determine the appropriate level of seismic retrofit with 

the lowest visual impact on the significant spaces, features, and 

finishes of both the interior and exterior of historic buildings. 

As with the illustrations above, this guide is not intended to 

proscribe how seismic retrofit should be done, but rather, to 

illustrate that every physical change to a building will have some 

consequence. By asking how impacts can be reduced, the owner 

will have several options from which to choose. 

• Can bracing be installed without damaging decorative 

details or appearance of parapets, chimneys, or balconies? 

KEY QUES 

• Are the visible features of the reinforcement, such as anchor 

washers or exterior buttresses adequately designed to blend 

with the historic building? 

• Can hidden or grouted bolts be set on an angle to tie floors 

and walls together, instead of using traditional bolts and 

exposed washers or rosettes on ornamental exteriors? 

• Are diagonal frames, such as X, K, or struts located to have a 

minimal impact on the primary facade? 

• Are they set back and painted a receding color if visible 

through windows or storefronts? 

• Can moment frames or reinforced bracing be added around 

historic storefronts in order to avoid unsightly exposed 

reinforcement, such as X braces, within the immediate 

viewing range of the public? 
I 

IN THE FOREFRONT 

Recommended 

• All original building ornamentation enhances the 

architectural value and should be retained and 

maintained. 

Recommended 

• Exterior bracing or buttressing should incorporate 

the building's natural lines. The exterior steel 

bracing appears to be an original building element 

because it runs parallel to the cornice line. 

Not Recommended • If it is determined that ornamentation must be 

secured or removed, effort should be made to secure it. The parapet of this building shows a "scar" where 

ornamentatIon was removed . 

IT- LS;:~'TL f-L ~~~~ _L t:r Of _L 

! 

tr: 

~ II "'" !!!!! 

ITT ~ 

Not Recommended • The exterior bracing on this building dominates its 

appearance. Care snould be taken to design exterior 

bracing to blend with or enhance the building's 

natural lines. 

Adapted from "Architectural Design Guide for Exterior Treatments of Unreinforced 

Masonry Buildings During Seismic Retrofit." Used with permission from the San 

Francisco Chapter, The American Institute of Architects. Drawings © Cassandra 

Mettling-Davis. 

STOASK: 

Securing Exterior Ornamentation: 

Ornament is one of the character-defining 

features of a building. Careful forethought 

and analysis should always precede 

alteration of a building's ornament. 

Generally methods to secure ornamentation by repair and reinforcing 

connections should be undertaken. 

Repairs or reinforcement should blend 

with the appearance of the ornamentation 

and should be designed to prevent future 

failures such as cracking due to thermal 

and seismic stress or unsightly differential 

weathering. 

If ornamental elements must be removed 

during the repair process, they should be 

reinstalled or replaced in-kind. The use of 

substitute materials may be acceptable if 

no other options exist. 

Exterior Buttresses: 

Exterior buttresses, an integral part of 

Gothic architecture, are not traditionally 

part of our architecture. In retrofitting an 

existing building, it is usually better to use 

an in-wall or interior bracing system rather 

than a visible exterior system. When used 

as an exterior bracing system, care must be 

taken to avoid damage to existing decorative elements. Even if saved, exterior buttresses can obscure decorative elements. 

Another problem requiring careful study 

is the integration of the buttresses with the 

existing structural system. Their attachment penetrates the building skin making 

the building more vulnerable to moisture 

damage. In a few cases where the interior 

building fabric is highly significant, exterior buttresses may be preferred. Care 

should be taken to avoid damage or 

obscuring existing architectural details. 

• Can shorter sections of reinforcement be "stitched" into 

the existing building to avoid removal of large sections of 

historic materials? This is particularly true for the 

insertion of roof framing supports. 

• Should base isolation, wall damping systems, or core 

drilling be considered? Are they protecting significant 

materials by reducing the amount of intervention? 

• Can shear walls be located in utilitarian interior spaces to 

reduce the impact on finishes in the primary areas? 

• Are there situations where thinner applied fiber reinforced 

coating would adequately strengthen walls or supports 

without the need for heavier reinforced concrete? 

• Can diaphragms be added to non-significant floors in 

order to protect highly decorated ceilings below, or the 

reverse if the floor is more ornamental than the ceiling? 

• Are there adequate funds to retain, repair, or reinstall 

ornamental finishes once structural reinforcements have 

been installed? 

• Are the seismic treatments being considered "reversible" 

in a way that allows the most amount of historic materials 

to be retained and allows future repair and restoration? 

10. Keeping preservation in the forefront is a critical aspect of 

seismic retrofit of historic buildings. These key questions will 

help keep preservation in mind as decisions are made about how 

best to improve the structural performance of historic buildings. 

q 
10 

If through-bolts are used, 

consider exterior appearance 

in location and detailing of 

bolt plates 

If exterior appearance is sensitive, consider grouted bolts 

New steel angle brace attached to existing roof 

Masonry wall 

12. Bracing parapets, as illustrated here, and supporting chimneys 

using metal struts or ties, are simple methods to protect these heavy 

elements from fa lling. Drawing: Architectural Resources Group. 

• Bolt sill plates to foundations and add plywood 

stiffeners to cripple wall framing around wood 

frame buildings. Keep reinforcement behind 

decorative crawlspace lattice or other historic 

features. 

• Reinforce floor and roof framing connections to 

walls using joist hangers, metal straps, threaded 

bolts, or other means of mechanical fasteners. Tie 

columns to beams; reinforce porch and stair 

connections as well. 

• Repair weakened wooden structural systems by 

adding, pairing, or bracing existing members. 

Consider adding non-ferrous metal straps in 

alternating mortar jOints if extensive rep ointing is 

done in masonry walls. 

• Reinforce projecting parapets and tie parapets, 

chimneys, balconies, and unsecured decorative 

elements to structural framing. Make the 

connections as unobtrusive as possible. In some 

cases, concrete bond beams can be added to 

reinforce the top of unreinforced masonry or adobe 

walls. 

• Properly install and anchor new diaphragms, such 

as roof sheathing or subflooring, to the walls of a 

structure prior to installing finish materials. 

• Avoid awkwardly placed exposed metal plates or 

rosettes when using threaded bolts through 

masonry walls. When exposed plates will interfere 

with the decorative elements of the facade, use less 

visible grouted bolts or plates that can be set 

underneath exposed finished materials. 

• Use sensitively designed metal bracing along 

building exteriors to tie the unsupported face of 

long exterior walls to the floor framing. This is 

often seen along side or party walls in commercial 

or industrial buildings. 

Rehabilitation 

When buildings are being rehabilitated, it is generally the 

most cost effective time to make major upgrades that affect 

the structural performance of the building (see illus. 13-17). 

New elements, such as concrete shear walls or fiber 

reinforcing systems can be added while the structure is 

exposed for other rehabilitation or code compliance work. 

• Inspect and improve all lateral tie connections and 

diaphragms. 

13. Installing diago nal frallles, underway in this rehabilitation, are a 

traditional method of seismic reinforcement. To reduce the impact of the 

X, K, or diagonal braces, they should be on the inside of the perimeter 

wall, designed to cross behind solid walls as much as possible, and 

painted a receding color where visible. Photo: David Look. 

steel moment frame 

14. The use of a steel moment frame to support the large open storefront 

during a rehabilitation eliminated the need to place diagonal braces or 

other illtrusive supports in a highly visible area of a historic building. 

Photo: David Look. 

15. The use of fiber composite materials can enhance the shear capacity of existing structural components -beams, columns, and surface elements, 

such as walls and floors. In this roofing application, the existing roof 

diaphragm is being strengthened and there is additional benefit to the 

shear reinforcement of the parapet wall. Photo: The Crosby Group. 
16. During the extensive rehabilitation of this historic building, new concrete, behind the new plaster finishes, strengthened the exterior brick 

walls and additional roof reinforcement was hidden behind the repaired/ 

recollstructed coffered ceiling. Photo: © !onathal1 Ferrar, courtesy 

UCLA Capital Programs. 

• Reinforce walls and large openings to improve shear 

strength in locations of doors, windows, and 

storefront openings. Carefully locate "X" and "K" 

bracing to avoid visual intrusion, or use moment 

frames, which are a hidden perimeter bracing in large 

openings. From a preservation perspective, the use of 

a more hidden system in finished spaces is generally 

preferable. 

• Strengthen masonry walls or columns with new 

concrete reinforcement or fiber wrap systems. A void 

the use of heavy spray concrete or projecting 

reinforced walls that seriously alter the historic 

relationship of the wall to windows, trim, and other 

architectural moldings or details. 

17. The internal grout illjection of rubble walls can improve seismic capacity. Care must be taken in formulating the mortar grout and 

repairing the area where injection occurs. Photo: Architectural 

Resources Group, San Francisco. 

• Selectively locate new shear walls constructed to 

assist the continuous transfer of loads from the 

foundation to the roof. If these walls cannot be set 

behind historic finishes, they should be located in 

secondary spaces in conjunction with other types of 

reinforcement of the primary spaces or features. 

• Consider the internal grouting of rubble masonry 

walls using an injected grout mixture that is 

compatible in composition with existing mortar. 

Ensure that exposed areas are repaired and that the 

mortar matches all visual qualities of the historic 

mortar joints in tooling, width, color and texture. 

• Evaluate odd-shaped buildings and consider the 

reinforcement of corners and connections instead 

of infilling openings with new construction. Altering the basic configuration and appearance of 

primary facades of buildings is damaging to those 

qualities that make the building architecturally 

significant. 

Specialized Technologies 

New technologies, being developed all the 

time, may have applicability to historic 

preservation projects. These specialized 

technologies include: vertical and center core 

drilling systems for unreinforced masonry 

buildings, base isolation at the foundations, 

superstructure damping systems, bonded 

resin coatings, and reproducing lost elements 

in lighter materials (see illus. 18-20). 

However, many new technologies may also 

be non-reversible treatments resulting in 

difficulties of repair after an earthquake. The 

reinforcement of historic materials with 

special resins, or the use of core drilling to 

provide a reinforced vertical connection from 

foundation to roof may not be as repairable 

after an earthquake as would more traditional 

means of wall reinforcement. New 

technologies should be carefully evaluated by 

the design team for both their benefits as well 

as their shortcomings. 

18. Oakland City Hall, California, completed in 1914, was restored to its original appearance and the computer model illustrates the comprehensive methods used to fu lly reillfo rce the 

building for the future. Photo: © Vittoria Visuals; Computer Model: © Douglas Symes, Sa n 

Francisco. VBN, Architects and Carey & Co, Inc. Architecture. 

Using computer modeling of how historic 

buildings may act in an earthquake suggests 

options for seismic upgrade using a 

combination of traditional methods and new 

technologies. While most projects involving 

base isolation and other complex damping 

11 
19. A system of core drilling, shown here, removes internal cored sections 

of unreinforced masonry from roof to fOllndations and fills them with 

grout and reinforcing rods. This may be an option for some 1I1lreinforced 

lI1asonry buildings with significant interiors and exteriors, although it is 

a less reversibLe treatment thall traditionaL diagonal frames or shear walls. 

Photo: David Look. 

20. The new base isolator allows the structural support member at the 

foundation to move horizontally as it absorbs the earthquake forces. 

While expensive, base isoLation may be justified by reducing the amount 

of damage to interior finishes and features with traditional methods of 

seismic retrofit. Photo: Photo: © Jonathan Farrer, courtesy UCLA, 

CapitaL Programs. 

systems constitute only a small percentage of the projects 

nationwide that are seismically reinforced, they may be 

appropriate for buildings with significant interior spaces 

that should not be disturbed or removed during the retrofit. 

Each building will needs its own survey and evaluation to 

determine the most appropriate seismic reinforcement. 

Post-Earthquake Issues 

12 

Should a historic building suffer damage during an 

earthquake, it is the owner who has a plan in place who will 

be able to playa critical role in determining its ultimate 

fate. If the owner has previously assembled a team for the 

purpose of seismic upgrading, there is a greater chance for 

the building to be evaluated in a timely fashion and for 

independent emergency stabilization to occur. In most 

municipalities, a survey, often by trained volunteers, will 

be conducted as soon as possible after an earthquake, and 

buildings will be tagged on the front with a posted notice 

according to their ability to be entered. Typically red, 

yellow, and green tags are used to indicate varying levels of 

damage-no entry, limited entry, and useable-to warn 

citizens of their relative safety. Heavily damaged areas are 

often secured off-limits and many red tagged, but 

repairable, buildings have been torn down unnecessarily 

because owners were unable to evaluate and present a 

stabilization plan in time (see illus. 21). Owners or members 

of the preservation community may engage their own 

engineers with specialized knowledge to challenge a 

demolition order. Because seismic retrofit is complex and 

many jurisdictions are involved, the coordination between 

various regulatory bodies needs to be accomplished before 

an earthquake. 

21. Without a plan in place before all earthquake, buiLdings that could be 

repaired are often torn dowl1. The loss of significant numbers of buildings 

within historic districts call further erode the financial alld Cllitural assets 

of an area. Photo: David Look. 

During times of emergencies, many communities, banks, 

and insurance agencies will not be in a position to evaluate 

alternative approaches to dealing with damaged historic 

buildings, and so they often require full compliance with 

codes for new construction for the major rehabilitation 

work required. Because seismic after-shocks often create 

more damage to a weakened building, the inability to act 

quickly-even to shore up the structure on a temporary 

basis-can result in the building's demolition. Penetrating 

rain, uneven settlement, vandalism, and continuing aftershocks can easily undermine a building's remaining 

structural integrity. Moreover, the longer a building is 

unoccupied and non-income-producing, the sooner it will 

be torn down in a negotiated settlement with the insurance 

company. All of these factors work against saving 

buildings damaged in earthquakes, and make having an 

action plan essential. 

Having an emergency plan in place, complete with access 

to plywood, tarpaulins, bracing timbers, and equipment, 

will allow quick action to save a building following an 

earthquake. Knowing how the community evaluates 

buildings and the steps taken to secure an area will give the 

owner the ability to be a helpful resource to the community 

in a time of need. 

If the federal government is asked to intervene after a 

natural disaster, technical assistance programs are 

available. Often after a disaster, grant funds or low-cost 

loans from federal, state, and congressional special 

appropriations are targeted to qualified properties, which 

can help underwrite the high cost of rehabilitation (see 

information about FEMA on page 15.) 
Conclusion 

Recent earthquakes have shown that historic buildings 

retrofitted to withstand earthquakes survive better than 

those that have not been upgraded. Even simple efforts, 

such as bracing parapets, tying buildings to foundations, 

and anchoring brick walls at the highest, or roof level, have 

been extremely effective. It has also been proven that well 

maintained buildings have faired better than those in poor 

condition during and after an earthquake. Thus, maintenance and seismic retrofit are two critical components for the 

protection of historic buildings in areas of seismic activity. 

It makes no sense to retrofit a building, then leave the 

improvements, such as braced parapets or metal bolts with 

plates, to deteriorate due to lack of maintenance. 

Damage to historic buildings after an earthquake can be as 

great as the initial damage from the earthquake itself. The 

ability to act quickly to shore up and stabilize a building 

and to begin its sensitive rehabilitation is imperative. 

Communities without earthquake hazard reduction plans 

in place put their historic buildings-as well as the safety 

and economic well-being of their residents - at risk. 

Having the right team in place is important. Seismic 

strengthening of existing historic buildings and knowledge 

of community planning for earthquake response makes the 

professional opinions of the team members that much more 

important when obtaining permits to do the work. Local 

code enforcement officials can only implement the 

provisions of the model or historic preservation codes if the 

data and calculations work to ensure public safety. 

22. When undertaking a substalltial rehabilitation to include seismic 

reinforcement, it is also an opportune time to restore lost or damaged 

features. The owner of this commerciaL buiLding, using the Historic 

Rehabilitation Tax Credits, restored the original bay and parapet gable, 

alld stone detailing that had been removed in an earlier insensitive 

remodeLing. Photo: David Look. 

23. Both exteriors and interiors can be severeLy damaged in an earthquake. This Craftsman Style bungalow was successflllly restored and seismically 

upgraded after the Northridge eartllquake in CaJifomia. Photographs: Historic Preservation Partners in Earthquake Response. 

13 
Buildings do not need to be over-retrofitted. A costeffective balance between protecting the public and the 

building recognizes that planned for repairable damage can 

be addressed after an earthquake. Engineers and architects, 

who speciaLize in historic buildings and who have a working 

knowledge of alternative options and expected performance for historic structures, are critical to the process. 

It is clear that historic and older buildings can be 

seismically upgraded in a cost-effective manner while 

Seismic Risk Zones 

Most local jurisdictions measure 

seismic risk based on seismic zones 

established by code, such as the 

Uniform Building Code with its 4 risk 

zones [1=low to 4=highJ. There are 

also maps, such as this one, which 

identify the Effective Peak 

Acceleration (EPA) which further 

reflect the light, moderate, and severe 

shaking risks as a percentage of the 

acceleration of gravity that can be 

expected in an area. 

In the United States, the greatest 

activity areas are the western states, 

Alaska, and some volcanic island 

areas. However, noted historical 

earthquakes occurred in 

Massachusetts (1755), Missouri (1811), 

South Carolina (1886), and Alaska 

(1964). The Caribbean Islands and 

Puerto Rico have been sites of severe 

earthquakes. The history of 

earthquakes in the United States has 

been recorded for over 200 years and 

new areas of concern include 

moderate risk areas in southern and 

mid-western states. 

The Richter Magnitude Scale, first 

published in 1935, records the size of 

an earthquake at its source, as 

measured on a seismograph. 

Magnitudes are expressed in whole 

numbers and decimals between 1 and 

9. An earthquake of a magnitude of 6 

or more will cause moderate damage, 

while one of over 7 will be considered 

a major earthquake. It is important to 

remember that an increase of one 

whole number on the Richter Scale is 

a tenfold increase in the size of the 

earthquake. 

retaining or restoring important historic character-defining 

qualities (see illus. 22, 23). Seismic upgrading measures 

exist that preserve the historic character and materials of a 

buildings. However, it takes a multi-disciplined team to 

plan and to execute sensitive seismic retrofit. It also takes 

commitment on the part of city, state, and federal leaders to 

ensure that historic districts are protected from needless 

demolition after an earthquake so that historic buildings 

and their communities are preserved for the future. 

ALASKA 

HAWAII 

.... '::::;:: , ,' "" ' ,' ~ c::? •

.................................... 

PUERTO 

RICO 

SHAKING 

INTENSITY 

LIGHT 

c:;9-

MOD E RATE IL. "··........::.... ·····'-----l 

SEVERE 

24. Seismic Map. The shading indicate areas in the United States and Puerto Rico that are affected by the probability of varying shaking intellsities. 

The risk of severe shaking is not limited to the west coast. Map: adapted from Federal Emergency Managemel1t Agency, FEMA 74 Guide. 

14 
FURTHER READING 

BuiLdings at Risk: Seismic Design Basics for Practicing 

Architects. Washington, DC AlAI ACSA Council on 

Architectural Research. February, 1992. 

Controlling Disaster: Earthquake-Hazard Reduction for 

Historic BuiLdings. Washington, DC National Trust for 

Historic Preservation. 1992. 

Earthquake-Damaged Historic Chimneys: A Guide to 

the Rehabilitation and Reconstruction of Chimneys. 

Oakland, CA. Historic Preservation Partners for 

Earthquake Response. July, 1995. 

Eichenfield, Jeffrey. 20 TooLs That Protect Historic 

Resources After an Earthquake; Lessons Learned from the 

Northridge Earthquake. Oakland, CA. California 

Preserva tion Founda tion.1996. 

History at Risk, Lama Prieta: Seismic Safety & Historic 

BuiLdings. Oakland, CA. California Preservation 

Foundation. 1990. 

Kariotis, John C, Roselund, Nels; and Krakower, 

Michael. Lama Prieta, An Engineer's Viewpoint. Oakland, 

CA; California Preservation Foundation, 1990. 

Langenbach, Randolph. "Bricks, Mortar, and 

Earthquakes; Historic Preservation vs. Earthquake 

Safety." Apt Bulletin, Vol.21, Nos.3/4 (1989), pp.30-43. 

Langenbach, Randolph. "Earthquakes: A New Look at 

Cracked Masonry." CiviL Engineering. November, 1992. 

pp.56-58. 

NEHRP Commentary on the GuideLines for the Seismic 

Rehabilitation of Buildings ( second ballot version). 

Washington, DC Building Seismic Safety Council 

(Prepared for Federal Emergency Management Agency) 

Draft, April, 1997. FEMA 274. 

NEHRP Handbook of Techniques for the Seismic 

Rehabilitation of Existing BuiLdings. Washington, DC 

Building Seismic Safety Council (Prepared for Federal 

Emergency Management Agency) 1992. FEMA 273. 

The Secretary of the Interior's Standards for RehabiLitation 

with IlLustrated GuideLines for Rehabilitating Historic 

BuiLdings. Washington, DC Government Printing Office, 

1992. 

Seismic Retrofit Alternatives for San Francisco's Unreinforced 

Masonry BuiLdings: Estimates of Construction Cost & 

Seismic Damage. San Francisco, CA. City and County of 

San Francisco Department of City Planning (prepared by 

Rutherford & Chekene, Consulting Engineers). 1990. 

The Seismic Retrofit of Historic BuiLdings Conference 

Workbook. San Francisco, CA. Association for 

Preservation Technology, Western Chapter. 1991. 

[contains an excellent bibliography of additional 

sourcesl. 

Schuller, M.P. Atkinson, RH. and Noland, J.L. 

"Structural Evaluation of Historic Masonry 

Buildings." APT BuLLetin, Vol 26, No. 2/3,pp. 51-61. 

State HistoricaL Building Code. Sacramento, CA: State 

Historical Building Code Board, 1990. 

Uniform Code for BuiLding Conservation. Whittier, CA: 

International Conference of Building Officials, 1991. 

The Federal Emergency Management Agency 

The Federal Emergency Management Agency (FEMA) -

is an independent agency of the federal government, 

reporting to the President. Since its founding in 1979, 

FEMA's mission has been to reduce loss of life and 

property and protect our nation's critical infrastructure 

from all types of hazards through a comprehensive, 

risk-based, emergency management program. FEMA 

works with the state and local governments and the 

private sector to stimulate increased participation in 

emergency preparedness, mitigation, response and 

recovery programs related to natural disasters. To 

minimize damage-repair-damage cycles, FEMA carries 

out and encourages preventive activities referred to as 

hazard mitigation. 

The FEMA Hazard Mitigation Program, established in 

1988 with the passage of the Robert T. Stafford Disaster 

Relief and Emergency Assistance Act, offers a framework for protecting historic structures from natural 

disasters. In the event of a federally declared disaster, 

state and local governments as well as eligible non-profit 

applicants may receive financial and technical assistance 

to identify and carry out cost-effective hazard mitigation 

activities. 

FEMA encourages hazard mitigation projects, including 

the restoration of buildings, by providing technical 

assistance and funding through the Hazard Mitigation 

Grant Program (HMPG), which can underwrite up to 

50% of the cost of the project. 

FEMA's public-assistance program provides financial 

and other assistance to rebuild disaster-damaged 

facilities that serve a public purpose, such as schools, 

hospitals, government buildings and public utilities. 

In terms of technical assistance, FEMA, under a 

cooperative agreement with the Building Seismic Safety 

Council has produced two volumes of comprehensive 

material dealing with the seismic retrofit of existing 

buildings (see Further Reading). In addition an ongoing 

project ATC-43 involves earthquake analysis procedures 

for Unreinforced Masonry Buildings and Reinforced 

Concrete Buildings. These documents contain nationally 

applicable technical criteria intended to ensure that 

buildings will withstand earthquakes better than before. 

There is a great deal of information that is applicable to 

historic buildings, although historic buildings are not 

necessarily identified as a category. Write for FEMA 

publications at: 

FEMA, PO Box 70274, Washington, DC 20024 

For current information about emergency activities, 

federally declared disaster areas, or how to contact 

regional offices see the 

FEMA website: http://www.fema.gov / 

For additional information on cultural resource 

preservation and Historic Rehabilitation Tax Credits see 

the National Park Service's 

NPS website: http://www.cr.nps.gov / 

15 
16 

Before After 

" 

25. While it is best to seismically retrofit historic buildil1gs before an earthquake strikes, if earthquake damage is to be repaired, it should be done in a 

manner respecting the historic character of the building. For this ca. 1925 Mediterranean Revival style building damaged in the Northridge Earthquake in 

California, financial and planning assistance from the Historic Preservation Partners for Earthquake Response made possible a sensitive rehabilitation. New 

structural steeL and restoration of the historic stucco and decorative tile work and a repaired tiLe roof reinstated this earthquake damaged buiLding as a major 

eLement of the historic district. Photo: Courtesy Historic Preservation Partners for Earthquake Response, M2A Architects. 

The Historic Preservation Partners for Earthquake Response 

was formed after the Northridge Earthquake of 1994 and 

was comprised of members of the National Park Service, the 

National Trust for Historic Preservation, The Getty 

Institute, The California Office of Historic Preservation, the 

California Preservation Foundation, and the Los Angeles 

Conservancy. After the earthquake, this organization 

provided technical assistance and grant funding to various 

historic buildings. Funding of 10 million dollars from the 

Acknowledgements 

David W. Look, AlA, is the Chief, Cultural Resource Team, 

Pacific Great Basin Support Office, National Park Service. 

Terry Wong, PE, is the Chief, Structural Engineering, 

Denver Service Center, National Park Service. Sylvia Rose 

Augustus, is the Historical Architect, Yosemite National 

Park 

The authors wish to thank their collaborator, Sharon C. 

Park, FAIA, Senior Historical Architect, Heritage 

Preservation Services, NPS, who undertook the technical 

editing of the publication and took the authors' original 

manuscript and developed it into the Preservation Brief 

complete with compiling information from other sources 

and selecting the photographs. Kay D. Weeks and Michael 

J. Auer, Heritage Preservation Services, NPS, contributed 

substantially to the published manuscript by revising the 

draft with an eye to articulation of policy, organizational 

structure, and cohesiveness of language. 

The authors also wish to thank the following for providing 

information for the publication and/ or reviewing the final 

draft: Steade R. Craigo, AlA, Senior Restoration Architect, 

State of California; Randolph Langenbach, Architect, 

FEMA; Bruce Judd, FAIA, Architectural Resources Group; 

Melvyn Green & Associates; Cassandra Mettling-Davis and 

Carey & Co. Inc. Architecture; Curt Ginther, Architect, the 

ISSN: 0885 7016 

National Park Service, U.S. Department of the Interior, was 

made available for the restoration and rehabilitation of 

cultural resources damaged during this natural disaster. In 

addition, sub-grants were provided by the National Trust 

for Historic Preservation and the California Office of 

Historic Preservation. A number of projects assisted by the 

Historic Preservation Partners for Earthquake Response are 

included and used with permission in this Preservation Brief 

University of California, Los Angeles (UCLA) Capital 

Program; The Crosby Group; American Institute of 

Architects, San Francisco Chapter; Jeffrey L. Eichenfield, 

California Preservation Foundation; Michael Jackson, 

Illinois Historic Preservation Agency; George Siekkinen, the 

National Trust for Historic Preservation; and colleagues at 

Heritage Preservation Services, NPS, including: de Teel 

Patterson Tiller, Chief; Charles E. Fisher, Anne E. Grimmer, 

John Sandor, and Jason Fenwick. 

This publication has been prepared pursuant to the 

National Historic Preservation Act, as amended, which 

directs the Secretary of the Interior to develop and make 

available information concerning historic properties. 

Comments about this publication should be directed to 

de Teel Patterson Tiller, Chief, Heritage Preservation 

Services Program, National Park Service, 1849 C Street, 

NW, Washington, DC 20240. This publication is not 

copyrighted and can be reproduced without penalty. 

Copyrighted photographs included in this publication may 

not be used to illustrate publications other than as 

referenced in this Preservation Brief without permission of 

the owners. Normal procedures for credit to the authors 

and the National Park Service are appreciated. 

Front Cover. Historic buildings damaged by earthquakes can be 

rehabilitated and seismically retrofitted. The posted tag in the window 

warns that this building, temporarily, cannot be entered. 

Photo: David Look. 

October, 1997