Earthquake Retrofitting and Seismic Upgrades
Many of our customers tell us they do not know what questions they should be asking. While the basics of earthquake retrofitting are simple, the retrofitting process can be complex. For this reason we have listed a number of frequently asked questions with detailed answers.
- How do I know whether my house needs earthquake improvements?
- How much does a complete residential earthquake retrofit cost?
- My house has been through several earthquakes, particularly the 1989 Loma Prieta Earthquake, without damage. Does that mean that it does not need to be strengthened?
- Are there any options regarding the amount of improvement to make?
- Do I need to have my seismic improvement planned by an engineer?
- How are your company and it’s employees qualified to recommend such earthquake improvements?
- Knowledgeable people have told me that my house is well built. Do I still need to make improvements?
- Will your recommendations follow the standards of the building code?
Will you bring my house up to code?
- Will you obtain a building permit to do my seismic improvements?
Why is a permit needed if there is no applicable retrofitting code?
- Can I do the retrofitting myself?
Or, can I do portions of the work myself in order to reduce the cost?
- My house already has foundation bolts. Does it need more strengthening?
- What kind of bolts do you use?
Is there any risk of damaging my foundation when bolts are added?
- What are holdowns?
- I have read that both bolting and bracing of a house are recommended. What is bracing?
- Are seismic improvements recommended if my house does not have a cripple wall?
- Can you give me a brief summary of the purpose of bolting and bracing?
- My foundation is pretty old and has a few cracks. Can I do the retrofit, or do I have to replace the foundation?
- My house has a brick foundation. Is retrofitting to a brick foundation advisable?
- How big an earthquake will a retrofitted house go through without damage?
- Will my insurance company give me a better rate after retrofitting?
- Does retrofitting increase a home’s value?
- How long will it take to retrofit my house?
- How disruptive is retrofitting work?
How do I know whether my house needs earthquake improvements?
Some information about the earthquake resistance of your house can be obtained simply from knowing when it was constructed. Almost any house built before the 1980s can be improved in such a way as to reduce earthquake risk. Even some houses built in the 1980s can be improved. Houses built 1990 or after usually have the earthquake resistive features installed during the original construction.
Seismic failures occur when a house either is displaced from (slides off) its concrete foundation, or when walls below main floor areas of the house collapse. In the first case, improvement consists of strengthening the connections between the house and the foundation. Improvements to prevent the second type of failure consist of both supplementing any existing connections to the foundation and strengthening the sub-area supporting walls.
The existing strength of your home, as well as its earthquake vulnerabilities, can be determined through a visual inspection by a trained and experienced earthquake specialist. Typically, this person will make recommendations for strengthening which, if implemented, will reduce the risk of both damage to the property and personal injury to its occupants.
Earthquake Safety will complete this visual inspection for you at no charge and with no obligation. Your decision to improve your home is based on our recommendations as well as your own personal assessment of the risk level your either have or desire to have.
How much does a complete residential earthquake retrofit cost?
There is no such thing as a standard house or standard earthquake retrofit. Accordingly, this is not a simple question to answer in the abstract. Larger and more complex houses, such as houses with split floor levels, cost more to earthquake retrofit than smaller and simpler ones. Ease of access will also affect your retrofit cost.
The typical cost to completely earthquake retrofit a medium size home with one floor level, a crawl space area relatively free of obstructions and in good condition, and with wooden framed walls in the crawl space (referred to as cripple walls) is about $4,000 to $7,000. A house of similar size and good access, but with no cripple wall (where the floor platform sits directly on the concrete foundation), can have connection improvements installed for $3,000 to $6,000. Larger homes, homes with many floor levels, steep hillside homes, and homes with finished basement area rooms, or homes with rooms over garages will cost more to retrofit. In these situations, a complete earthquake retrofit can cost $10,000 or more.
Whatever your home needs, Earthquake Safety will do a complete inspection, develop an improvement plan, and present you with a proposal to make the improvements at no cost or obligation. Most frequently, our proposals will contain several separately priced options to allow you to consider a variety of earthquake improvement solutions.
My house has been through several earthquakes, particularly the 1989 Loma Prieta Earthquake, without damage. Does that mean that it does not need to be strengthened?
While it is fortunate that you did not have previous damage, and this certainly gives comfort, it would be a mistake to rely on such a past experience to predict the effects of any future earthquakes.
There are a number of factors that affect the severity of earthquake damage. These include soil conditions, how a house was built, length and strength of the shaking. Most critical, however, is the distance between your home and the source of the earthquake; its epicenter.
The USGS (U.S. Geological Survey) shows in its 1990 public information booklet, The Next Big Earthquake, a very dramatic graphic comparing shaking strength with distance from an epicenter. This graphic makes several comparisons with the 1989 Loma Prieta Earthquake, measuring 7.1 on the Richter Scale, and with the epicenter on the San Andreas fault in the Santa Cruz mountain area. Interpreting this graphic takes a bit of study. Its implications can be understood by taking just one example. If the epicenter of this same 7.1 earthquake were on the Hayward fault in the Oakland hills, instead of in the Santa Cruz area, shaking in the Oakland hills would be 12 times as strong as it was in that locality in 1989. By moving the same size earthquake some 60 miles closer, the intensity of the shaking is increased many fold. How much will the ground shake?
This is the bottom line. An earthquake of about the same magnitude as the 1989 Loma Prieta Earthquake is being predicted for the Bay Area. If this happens, the strength of shaking in Bay Area cities will be much greater than in 1989, as much as 12 times as strong. Relying on the 1989 experience is risky. Preparations need to include expectations for an intensity of shaking never before experienced by most homes in the Bay Area and surrounding communities.
Are there any options regarding the amount of improvement to make?
Yes, certainly. Decisions about earthquake-related improvements are very much like decisions about safety features to include when buying a new car. More features cost more, but they will also provide greater reduction in the risk of personal injury and property damage.
The expression "earthquake proof" is used in common language, but there is no such thing as an earthquake "proof" house. Also, there is no way to determine the exact improvement needs of an individual home. This is because the actual seismic stresses a home may experience are unpredictable.
Engineers can make calculations based on certain assumptions. Improvements can be made based on assumption of the worst possible earthquake situation. However, there may be situations where it is not possible for the homeowner to make all the recommended improvements because of budget or other considerations.
Also, given a choice, many of us would rather invest our home improvement budget in something other than seismic improvements. We have heard many variations in this homeowner dilemma: "... I would rather spend my limited home improvement money on things I can see and enjoy, like remodeling my kitchen. Yet, I don't want my remodeled kitchen to be lost if my house is ruined."
There is a way to make decisions about seismic improvements in spite of this dilemma. In order to both reduce earthquake risk and still have funds left to remodel the kitchen, we suggest some of the following as criteria for determining earthquake improvement priorities:
- Stage the improvements. Do some of the recommended improvements every year or so until all the desired improvements have been made. Identify the weakest and most vulnerable conditions in your home. Improve these first.
- Some improvements may be more important to improve safety rather than to protect the property. Do the safety-related improvements first.
- Do the improvements that may be more cost-effective, or possibly the simplest and most straightforward to install. Defer the more difficult or more disruptive improvements for later.
- If any remodeling is planned, make improvements in other areas first; defer the improvements in the planned remodel areas and make the seismic improvements during the remodeling work.
Even though improvements can be staged and even deferred, it is important to remember that full seismic protection will not be achieved until all recommended work is completed. However, if a full and complete retrofit is either not desired or affordable, the professional staff at Earthquake Safety will work with you to discuss and sort out some of these dilemmas and priorities.
Do I need to have my seismic improvement planned by an engineer?
An engineer's consultation is certainly an option. But, it is not required, since seismic improvements are voluntary. An engineer will charge a fee for such a consultation.
It is common and accepted practice for seismic improvements to be planned by a contractor, especially if the contractor is an experienced seismic specialist. In situations where our company's recommendations have been compared with those of an engineer, it has been unusual to find substantial differences. Such minor differences can also be found when making similar comparisons between two engineers.
There are situations where an engineer's consultation is advisable, or where engineered plans are necessary. These situations would be large, complex, multilevel houses; houses such as stilt houses on steep hillsides; houses with very large openings in lower level walls; or houses with severe foundation and/or drainage problems.
Our company inspectors will always advise you when they feel your situation is too complex, or otherwise beyond their knowledge and capability.
How are your company and it’s employees qualified to recommend such earthquake improvements?
Following the recent major earthquakes in California, various governmental agencies, private engineers, and university research groups have made extensive examinations of failed buildings, identifying failure points and other weaknesses in construction. Their observations along with their recommendations for construction improvements are found in research publications. Many of the recommendations have been adopted into revisions of the Uniform Building Code, especially since 1989, and have been incorporated into new buildings constructed since that time. Some, or even most, of the recommended corrective measures can also be added to existing structures, a practice commonly referred to as "seismic retrofitting", "seismic strengthening" or, more commonly, as bolting and bracing.
Additionally, the California Seismic Safety Commission, the Association of Bay Area Governments, and the International Conference of Building Officials have jointly sponsored training programs for contractors engaged in the business of offering seismic improvements for homeowners.
Reading and studying this literature as well as participation in the offered training courses is required for our inspection and supervisory staff. Professional staff members also receive one-on-one training during individual on-site consultations with engineers who work directly with the Earthquake Safety and its clients. The founders of the company have also visited several post-earthquake sites to learn first hand about building failure points.
At this time there is no formal accrediting agency or certification process for seismic retrofitting, even for engineers. Twenty years of experience, formal and informal training of employees, and the company's track record of over 6,500 retrofitted homes are the foundation for its expertise.
As a final note on expertise, it should also be pointed out that the training of employees who install the seismic improvements is also very important. The best-planned retrofit will not protect your home if it is not properly installed. The company's installation crews are fully trained and supervised by one of its owners. The company is very much committed to providing the best quality workmanship. Positive feedback about the quality of the work is received on an on-going basis. As one engineer who does regular home inspections has told us. Your company does "signature" work, meaning, he says, that when he sees an exceptionally good job he can tell immediately who did the work.
Knowledgeable people have told me that my house is well built. Do I still need to make improvements?
Most recommended strengthening practices stem from a report issued by the University of California, Engineering Department, in 1982. Other recommendations for seismic improvements come from field observations and reports issued by governmental agencies, private engineers, and other sources following major California earthquakes, particularly the 1989 Loma Prieta quake and the 1994 Northridge earthquake. Construction standards determined by either the Uniform Building Code, or by common practice, were changed considerably in the 1990s , following the recommendations of these reports.
Accordingly, if your home was built before these seismic standards were adopted, particularly before the 1980s, to the extent that your home can be upgraded to meet or be closer to these standards, you will be able to reduce its seismic risk. If your home was well built originally, seismic improvements may be of even greater value, since you will have both the quality of the original construction and the added improvements to reduce seismic risk. If you cannot count your house as being originally a well-built home, seismic improvement may be absolutely critical.
Will your recommendations follow the standards of the building code?
Will you bring my house up to code?
There is no current code for retrofitting for several reasons. Houses are very different in construction style, accessibility, and seismic vulnerability; it is difficult if not impossible to apply one standard to such a variety of situations and conditions. Attempts to develop a consensus among experts regarding retrofitting standards have not been very successful. Most importantly, though, is that the seismic retrofitting is voluntary; any homeowner can do as much or as little as he or she wishes.
One local building department has developed a "prescriptive plan" for retrofitting. Earthquake Safety follows this prescriptive plan when it is practical and feasible to do so. Again, though, because houses differ so much in style and construction and, mainly, because homeowners differ in their needs and their expectations, we have found that a customized plan will be necessary to accommodate any given retrofitting situation.
Earthquake Safety will prepare a customized improvement plan for you, drawing upon the current building code as well as many other sources as it is developed.
Will you obtain a building permit to do my seismic improvements?
Why is a permit needed if there is no applicable retrofitting code?
Most local building departments issue permits for seismic improvements; one or two cities have made exceptions for the very reason that there is no applicable code, or for other reasons particular to their department. (We will fully inform you regarding the requirements in your locality.)
The building department will not do what is commonly referred to as a "plan check", meaning a review of the proposed work by a staff engineer. This is because the work is considered to be voluntary on part of the homeowner. By voluntary it is meant that no specific improvements can either be required or not required by building department authority. The improvements you make are at your choosing entirely.
However, most local building departments are concerned that improvements are made competently. Their inspector will review the completed work, providing you an independent verification of proper installation. This means, of course, greater assurance of a good performance when the improvements are put to test during an actual earthquake situation. Specifically, inspectors will check the bolts and other hardware to make sure that attachments to the concrete and wood framing members make the strongest possible connections; that plywood used for shear improvements is properly cut and nailed; and other code-specified matters.
Inspectors also make sure that other peripheral code items are taken care of during the installation. If a plywood shear wall is to be built inside a garage, for example, code requires reinstallation of sheetrock over the new plywood to provide a fire barrier between the garage and living area of the house. There are also some other code-required installations that must be done whenever any building permit is involved. Smoke detectors in your home, for example, may need to be upgraded.
Contrary to the fears which homeowners sometimes express to us, we find that inspection by the building department is done to protect homeowners rather than to be annoying or harassing. Building inspectors are friendly and competent, and will not cause problems for people who know and follow the rules. The rules are there to assure health and safety, not just to be troublesome.
The retrofitting contractor will obtain the building permit and deliver it to your home. All permit documents are owned by you, and should be retained with your property records for future reference. They may be useful, particularly, for insurance purposes or for selling your property.
Can I do the retrofitting myself?
Or, can I do portions of the work myself in order to reduce the cost?
Of course you can retrofit your own home. However, many people who have attempted to do this have given up and called our company to complete the work, for several reasons. Many of the important details regarding the handling of problematic situations under a house are not covered in the very generalized do-it-yourself manuals. Making certain these details are handled properly often makes a critical difference in the quality and strength of the retrofit. Prior to the installation of a retrofit, a good plan is needed. Knowing what to do, where to do it, and how to do it are extremely important. Retrofitting is very hard work. Very undesirable and uncomfortable working conditions are found under most houses. Good tools and equipment are needed to help the work, to make sure it is well done, and to protect personal safety during the work.
Many homeowners find they can save money by doing some of the peripheral work themselves. Sometimes cabinets need to be removed and replaced. Plaster and other wall coverings may need to be removed and the debris handled. Many homeowners, especially if handy at all, choose to complete some of the preparation and follow-up work themselves to save some money, and leave the critical structural improvement work for the experts. We encourage this type of participation whenever it is practical.
My house already has foundation bolts. Does it need more strengthening?
It probably does. The simple answer to this question is that it is not enough just to see bolts. Weakened or insufficient bolt connections may lead to failure. Additionally, bolting and bracing are both needed. If the walls supporting a house are weak they may simply collapse from under it.
Code requirements for bolting as well as standard construction practice have changed in response to increased earthquake concerns, especially since 1990. Many houses have half-inch diameter sill bolts placed at intervals of six feet. The practice now is to install larger diameter bolts (5/8" or 3/4" depending on the scale of the home) at closer intervals. Additionally, since bolts primarily prevent lateral or sliding movements, other types of hardware called holdowns are installed to resist effects of the house lifting off the foundation during seismic movement.
The type of washer used also makes a considerable difference in seismic resistance. Following failures observed after the 1994 Northridge earthquake, the building code now requires the use of a larger, thicker, square washer in place of the small, thin, round washers that were used for many years. This has the effect of anchoring the sill from the top (clamping it down) rather than relying on the bolt extending through the wooden sill for sliding resistance. Northridge observers found situations of over-drilling, in which the hole drilled for the bolt was too large in diameter. This allowed for sill movement around the bolt, which split the wood. The clamping effect of the square washer compensates for this.
Most importantly, however, is that bolts do not last forever. Steel decays and loses its strength, particularly when a home has not had good foundation drainage. Rusted bolts cannot be detected by visual inspection alone, or in any other way short of costly testing. The decay does not reveal itself above the sill, but is inside the concrete where it cannot be seen. Bolt weakening is usually discovered only at failure. One engineer who has advised us thinks that new bolts should be added about every 30-40 years because of steel failure.
Many houses are built with the floor platform set directly on the foundation sill. In this case, even if the bolts are sound, the connection does not extend far enough into the floors and walls of the home to resist displacement. Read the answer to question 15 for more description of this situation.
What kind of bolts do you use?
Is there any risk of damaging my foundation when bolts are added?
General practice is to use either a mechanically anchored bolt, commonly referred to as an expansion bolt or wedge anchor; or a bolt that is bonded to the concrete with epoxy adhesive, commonly referred to as an epoxy bolt or epoxy-set bolt. Both material cost and installation time are greater for epoxy bolts; thus, they cost more to install.
Expansion bolts have a cone shaped base with a stainless steel sleeve wrapped around the bolt near this slightly widening base. A hole is drilled into the concrete a little deeper than the bolt length. The bolt is inserted into the hole. Then, as the nut of the bolt is tightened it draws the coned end into the sleeve, causing it to expand outward, and wedging the bolt into the hole at its base. The bolt is anchored to the concrete only at the base, and puts a light tension load on the concrete as it is wedged in place. Expansion bolts are recommended only if two conditions are met: the concrete is of sufficient strength to resist this wedging effect; the load that will be placed on the bolt during an earthquake situation will break the bolt off rather than pull it out of the concrete. In more technical language, an expansion bolt is designed to provide good resistance to shear load but not necessarily to tension load.
In older houses where the concrete may be weaker, or when a bolt is going to be asked to resist the effect of being pulled out of the concrete, the epoxy-set bolt is used. Epoxy-set bolts are installed by drilling a hole in the concrete slightly larger in diameter than the bolt, to give room for the epoxy material. The epoxy material is inserted into the hole in a liquid form, and the bolt is driven into the hole. After some set up time, the epoxy adheres to the concrete in a bonded attachment usually stronger than the concrete itself. Epoxy bolts are threaded the full length of the bolt. The epoxy material does not adhere well to the steel, but sets within the openings of the threaded steel, anchoring the bolt much like a screw is anchored within a hole in a piece of wood.
There are several advantages of epoxy-set bolts. They simply "rest" inside the hole in an unloaded, static state rather than placing a wedging stress on the concrete, as the expansion bolt does. The strength of the connection can be increased by installing a longer bolt, more deeply set into the concrete and with more length of attachment. The epoxy anchoring material is also impervious to water. Rusting and other decay of the bolt is reduced; bolt longevity is increased. Epoxy materials have been tested. Bolt manufacturers tell us that there is no reason to expect epoxy failure over time.
Thus, bolt choice is influenced by several factors: cost, condition and quality of the concrete, and the manner in which the bolt will be loaded. Most engineers recommend epoxy bolts for all mud sill bolting. If there is any doubt about the better choice, use the epoxy-set bolt.
The risk of damaging the concrete while installing the bolts is very minimal. Special drilling equipment is used in order to reduce this risk. The benefits achieved from retro-bolting far outweigh any very small risk.
What are holdowns?
Holdowns are special brackets designed to resist any effects where wooden framing members of a house may be pulled away from any intended anchors, most commonly its concrete foundations or walls. Usually, this is an upward or lifting effect in the walls of the house and, thus, comes the term "hold down". The conditions under which this lifting may occur are complex and difficult to explain in writing. We can explain them in a visual demonstration during our meetings with you.
Not all houses need holdowns. Holdowns may also be used as convenient anchoring brackets in situations where the lifting effect in not expected, but this is not usual.
I have read that both bolting and bracing of a house are recommended. What is bracing?
Many houses have a short wood framed wall, referred to as a "cripple wall", running from the foundation to the main floor. This wall needs to be strengthened to avoid seismic collapse. With this collapse, the house appears to have been vaulted to one side on its sub-area walls. Improvement in the stiffness of these walls is needed in order to transfer the earthquake movements from the ground through the cripple walls to the house. This forces the foundation and the house to move together.
Differential movement is reduced by turning some of the sub-area walls into "shear walls", which consists of attaching structural plywood to the walls to create the desired strengthening or stiffness.
Are seismic improvements recommended if my house does not have a cripple wall?
Many houses, especially those built in the 1960s and 1970s or later, are constructed with the floor framing set directly on the foundation sill. If this is the case, even if the bolting is sound, the connections may not extend far enough into the floors and walls to keep the house from sliding off its foundation.
Failures in past earthquake situations show the floor framing sliding off the bolted sill; a failure in the typically toe-nailed connection between bottom edge of the floor joist and the flat top surface of the bolted sill. Recently, construction technique has improved to compensate for this. Steel straps are set in the wet concrete as the foundation is poured. The straps then extend upward, across the flat sill, to connect into either the floor or wall framing of the house.
This connection between the foundation and the floor framing can be improved in existing homes by retrofitting struts. The struts consist of angle irons which, properly installed, add both a lateral or sliding resistance and a vertical or lifting resistance to the main body of the house. They extend the connection of the house to the foundation much further than is provided by the original bolts.
You can determine whether your house has a cripple wall simply by looking under it. If the sub-area walls are solid concrete extending to the floor, the addition of the steel struts is to be considered. If there are short walls with vertical wooden "studs", the sill will be bolted and the wall braced with plywood. Some houses will have a combination of both of these.
Can you give me a brief summary of the purpose of bolting and bracing?
Yes, as long as it is recognized that any brief summary requires oversimplification. Using the language of an engineer, we can say that retrofitting increases the ability of the sub-area of a house to transfer the "loads" or stresses of an earthquake, especially lateral loads, from the ground to the house so that everything moves together. In order to make this transfer, all connections must be in place and must be strong enough to complete the transfer of movement. Like the failure of the weakest link in a chain, if any transfer point fails, the house itself may fall, slide, or otherwise be moved off its concrete foundation. If this happens, extensive structural damage is likely to be the result.
Retrofitting a house consists of adding connectors, where they are found to be missing, or improving existing weak connections between the major structural elements of a house, or bracing of walls that are susceptible to collapse.
The desired end result is that the house moves as a unit with its foundation. The key is that all connections, not just bolts, in the path of movement must be in place and must be strong enough to complete the transfer of movement from each of the house's components to the next.
My foundation is pretty old and has a few cracks. Can I do the retrofit, or do I have to replace the foundation?
It would be nice if all houses had new, steel reinforced foundations, but they do not. It would also be nice if we all had the resources to replace foundations when they are in marginal condition, but we do not. Quite a dilemma--to own an older home, with a weak foundation, live in earthquake country, and have no money. New owners of older homes, particularly, may experience this dilemma, given the recent rapid increases in the cost of buying a home in the Bay Area.
The most important question is whether the concrete is strong enough to provide a good anchor for bolts. In some cases, it is obvious that foundation replacement is the only solution; one can simply see how weak the concrete is. In less clear situations, there are several options.
The strength of the concrete can be tested., at a significant cost. However, most homeowners prefer not to invest in the testing, since it does not help resolve the dilemma. If there are resources to replace the foundation, investing in the replacement rather than the testing seems to be the better choice. If there are no replacement resources, good test results may be reassuring, but poor test results are not very helpful. Earthquake Safety has informed many of its clients with marginal foundations of the availability of testing, but only three of many hundreds have chosen to have the testing done. The rest have relied on their own judgment, the judgment of our inspectors, or on others with experience in evaluating foundations.
Foundations can be evaluated visually and by sound. It is easy to see the crumbling of the concrete, signs of years of poor drainage, excessive subsidence, severe cracking and other conditions which suggest that the concrete will fail if heavily loaded. A light tap on the concrete with a steel hammer also reveals differential sounds, which say a lot. A sharp "ping" sound indicates decent core strength; a dull "thud" sound indicates poor strength. Minor cracks in the foundation are of concern, but not a reason to forego a seismic retrofit.
Under marginal conditions and with no replacement resources, anchoring to the existing concrete may still a good decision. Weaknesses in the concrete can be compensated for in a number of ways. There are two types of bolts used in retrofitting: expansion or wedge anchor bolts, which are used only with good concrete; and bolts anchored with an epoxy adhesive. With poorer concrete, the epoxy-anchored bolts are used. Also, both the strength of the connection and better distribution of loads can be accomplished by using more bolts, placing them closer together. Longer, deeply set epoxy bolts also anchor better in poorer concrete. If only parts of the foundation are weak, it may be possible to concentrate the improvements in the areas of the house with the better concrete, and still achieve worthwhile seismic risk reduction.
If you have questions about your foundation, the free inspection offered by our company may be a way to start to have them answered. We will give you our best and most straightforward opinion about the condition of your foundation, and discuss the possible solutions with you.
My house has a brick foundation. Is retrofitting to a brick foundation advisable?
No. You will need to have the brick foundation (or any portions that are brick) replaced before the remainder of the retrofitting can be done. Earthquake Safety does not replace or repair foundations. However, if you call our office, we will refer you to one of several firms who will be able to provide the necessary foundation replacement.
How big an earthquake will a retrofitted house go through without damage?
This question is asked frequently. Essentially, though, it is unanswerable. The movement during an earthquake is too complex, and there are too many unknowns to be able to answer this question directly.
In past earthquake situations, two houses built at about the same time, right next to each other, and with many other similarities have performed very differently. Size and shape of the house, condition of the concrete foundation, how well it has been maintained, modifications and changes in the original construction which may have created structural weakness, and many other variable factors will affect earthquake damage.
Given this, it is important to think of earthquake damage prevention as a risk reducing practice rather than have a more absolute expectation as to what may be accomplished. The comparison may be something like maintaining a good diet and exercising to reduce the risk of heart disease. Both are good health practices; they reduce the risk of a heart attack, but there is no guarantee of such.
The term risk reduction also means at least two things. The probability of any damage at all is reduced. Also, if there is damage, the extent of the damage is reduced (along with what may be required to repair the damage).
But, the news is good. Observations, made repeatedly, from past earthquake situations show that amount of damage, time required for repair and recovery, loss of property, and cost of repairs are significantly and considerably less in buildings where improvements have been made, even during the larger earthquakes. This is why engineers, building officials, insurance companies, public safety agencies and others who have observed past earthquake situations recommend, almost without exception, that homeowners have their houses improved for better earthquake resistance.
Will my insurance company give me a better rate after retrofitting?
We recommend that you ask your insurance agent to answer this question. Insurance company practices do change. At the time of this writing, the California Earthquake Authority (CEA) which provides the earthquake insurance you receive through many of the major home insurers, will reduce the cost of earthquake coverage by 5% if you have your home retrofitted. Some other private insurance companies will also reduce the cost of earthquake coverage. As far as we are aware, the cost of the more general homeowner's coverage is not changed when you retrofit. Many prospective home buyers have called us to say they needed to have their new houses improved (primarily bolted) before they could get insurance coverage. But, again, this is a question to ask of your insurance agent.
Does retrofitting increase a home’s value?
There is not enough available information to answer this question. To a large degree, it depends on both market conditions and the earthquake consciousness of any potential buyer of your property. A competed retrofit certainly adds to the marketing features of a home.
We have had customers tell us that a real estate professional or financial advisor has recommended against retrofitting because the cost is not recoverable in the market value of their home. This advice seems to be based on a twisted notion about the purpose of retrofitting. The purpose of retrofitting is not to increase property value, it is to help the homeowner reduce financial loss, make a better and faster recovery from a disaster situation, and protect the safety of the home's occupants.
A decision against making seismic improvements, regardless of the reason, is a gamble. It is a conscious decision to bet against the forecasts and recommendations of seismologists and other earthquake experts.
Another word of caution also seems appropriate here. When buying a home, we recommend having any previous seismic improvements inspected as a part of your purchase process. The thoroughness and quality of a seismic retrofit are very important when it comes to how the house will perform during an earthquake situation. We do not offer these services to home buyers, but will refer you to an engineer or other inspectors who are qualified to do this for you.
How long will it take to retrofit my house?
The average time for a complete retrofit is 3 days or less. A few homes can be done in one day. Larger homes or homes where there is need to open and re-close finished walls for work access will take longer. It is extremely rare to have a retrofit project take more than a working week.
One of the most common homeowner complaints about contractors is that a job takes too long. Or, once started, the contractor leaves, and seems never to return to complete the work. Finding out about the contractor's scheduling and work completion habits may be the most important thing you can do as you check a contractor's references. Earthquake Safety has a very good track record on this. Please verify it with the long list of references we provide to you.
How disruptive is retrofitting work?
If all the work is to be done in crawl space areas, which it is in most cases, the disruption will be minimal. This usually consists of no more than one to three days of two workers at your home, some noise coming from under the house and a van in front of it. Our workers are trained to clean up after themselves immediately, to not smoke at or near your home, to avoid playing radios loudly, and to comply with all reasonable homeowner requests. They are complimented regularly on their courtesy, efficiency, competency and politeness. This can all be verified by calling our past clients. An extensive list of references will be given to you at our first inspection visit to your home.
You will be asked to participate in the retrofitting process in the following ways.
- You will be asked to provide access to areas of your home that need to be seen during our initial inspection visit.
- Family members who participate in decision making about your home will be asked to sit down with our representative for a presentation and discussion of our improvement plan and proposal, usually taking about an hour.
- If you have any personal items stored in the areas where work needs to be done, you will be asked to temporarily move these items out of the way.
- You will be asked to arrange for the installation of code-required smoke detectors in bedrooms and hallway areas of your home, if this has not already been done.
- And finally, you will be asked to have an adult member of your household be present during the final inspection, by your local building inspector, which might require being home most of a full day.
LICENSED • BONDED • INSURED
CONTRACTOR LICENSE #519461