Earthquake Book

Governor’s Office of Emergency Services

?? Is the water heater free-standing?

?? Are there straps or other types of restraints

securing the water heater?

?? Are there straps or restraints bolted to the

studs?

?? Are there flexible pipes for water and gas

connected to the water heater?

Remember

?? Replacing a water heater after an earthquake

can cost more than $500.

?? Repairing fire damage and flooding damage

can cost several thousand dollars, including the

entire cost of your home!

?? There are many different ways of strapping a

water heater. One example is shown on the

next page. (See page 13)

?? Check with your local Building Department for

details of local requirements.

?? Know where your main water valve is so that

you can shut it off if you have a water leak.

?? Know where your main gas valve is so that you

can shut it off if you hear or smell a gas leak.

(See page 32)

Contents Damage

Unbraced Water Heaters

12 The Homeowner’s Guide to Earthquake Safety

Figure 10 - The unbraced water heater in

this home fell during an earthquake; the

resulting fire destroyed the home.

Water heater

Figure 11 - This unstrapped water heater

tipped over during the 1984 Morgan Hill

Earthquake. Fortunately gas and water

lines were not ruptured.

Guna Selvaduray

Comparison of Cost: Preventing vs. Repairing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

HOW-TO

Water heaters must be braced (securely attached) to the studs in a wall. California law requires water

heaters to be braced at the time of sale, or when a new water heater is installed.

How-to Resources

?? Your local home improvement store

?? How to Brace Your Water Heater, City of Los

Angeles, Department of Building & Safety,

Information Bulletin #P/PC 2002-003, June 14,

1999.

?? Guidelines for Earthquake Bracing of Residential

Water Heaters, Department of General Services,

Division of State Architect, August 11, 2004.

?? How to Secure Your Water Heater, Governor’s

Office of Emergency Services, 2003.

The Solution

There are many solutions – all relatively

inexpensive.

?? Purchase and install a strap kit or

bracing kit from your local hardware

store. Be sure the kit is certified by

the State Architect.

Other options include:

?? Have a licensed plumber strap your

water heater according to code.

?? Use metal tubing or heavy metal

strapping and lag screws and

washers to secure the water heater

to the wall studs.

The gas and water lines should also have

flexible pipes. These are safer than rigid

pipes during an earthquake.

Be sure to check the straps once a year.

They may come loose due to vibrations,

or other causes.

$20 to $200 $500 to total value of home (if completely destroyed).

The Homeowner’s Guide to Earthquake Safety 13

Brace Water Heaters

Figure 12: One Method of Water Heater Bracing. Straps

and screws visible with water heater in a garage installation.

You may need to add wood blocking.

Sheetrock

If wood blocking is used, it

must be attached to studs.

WATER

HEATER

Straps

Flexible

pipes

Houses that are not bolted to the foundation can

move off their foundations during earthquakes.

If your home has no foundation, or an old

concrete foundation, see page 30.

?? Go down into the crawl space – the area

between the first floor and the foundation – to

find out if your house is bolted to its foundation.

?? Look for the heads of anchor bolts that fasten

the sill plate – the wooden board that sits

directly on top of the foundation – securely to

the foundation. (See Figure 14a, page 15)

?? You should be able to see the large nuts,

washers, and anchor bolts, installed at least

every 4 to 6 feet along the sill plate. Steel

plates are sometimes used instead of anchor

bolts. (See Figure 14b, page 15)

Remember

?? It is very expensive to lift a house, and place it

back on its foundation.

?? Homes moving off their foundations can cause

gas lines to rupture, which in turn can result in

fires.

Home Not Anchored to Foundation

14 The Homeowner’s Guide to Earthquake Safety

Slab Foundations

Some homes are built directly on concrete slabs. These houses do not have crawl spaces

and cripple walls.

Nearly all homes with slab foundations that were originally built to code will have anchor

bolts or straps.

However, if the house is not bolted to the slab, you have an earthquake weakness.

Newer homes generally have anchor bolts or straps.

If you have an unfinished garage, you may be able to see the anchor bolts.

You are not required to remove siding, drywall or plaster to determine if your house has

anchor bolts.

Figure 13 - This home wasn’t bolted and slid off its

foundation. Sometimes the damage can be so bad that

houses have to be demolished.

Office of Emergency Services

Comparison of Cost: Preventing vs. Repairing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

HOW-TO

Figure 14 —Anchor bolts or steel plates. A home’s crawl

space may be formed by a cripple wall (see next page for

description) between the foundation and the floor joists or the

floor joists may rest directly on the sill plate. In either case,

you should be able to see the heads of anchor bolts or steel

plates installed at appropriate intervals. These fixtures fasten

the sill plate to the foundation.

The Solution

Drill holes through the sill plate into the foundation

and install anchor bolts. (See Figure 14a)

If there is not enough room to drill, you can attach

steel plates to hold the sill plate to the foundation.

(See Figure 14b)

Anchor bolts have to be installed properly for them to

be effective.

You must obtain the proper permits from your local

Building Department before beginning work.

SNCCCCtoooronnnuntttscteeeHttennnrunOutttrtssscaWs tlDDD u-DDTaaaraaaOmmmmlm aaaHaagggaggeeezeeards

How-to Resources

?? Detailed information for do-it-yourselfers or

engineers can be found in the International Existing

Building Code, published by the International Code

Council.

?? Publication: How You Can Strengthen Your Home

for the Next Big Earthquake in the Los Angeles

Area, City of Los Angeles, Department of Building

& Safety, October 2001.

Anchor Foundation

The Homeowner’s Guide to Earthquake Safety 15

$250 to $5,000 $25,000 to total value of home (if completely destroyed).

Figure 14b

CRAWL

SPACE

Steel plates

Floor joists

Wall stud

Concrete

foundation

CRAWL

SPACE

Sill Plate

Tops of

anchor bolts

Concrete

foundation

Wall studs

Floor joists

Figure 14a

Flooring

Wooden floors and stud walls are sometimes built

on top of an exterior foundation to support a house

and create a crawl space. (See Figure 17, page 17)

These are called cripple walls and they carry the

weight of the house.

During an earthquake, these walls can collapse if

they are not braced to resist horizontal movement.

If the cripple wall fails, the house may shift or fall.

SNCtoornnutscettnruutrsca tlD uDaraamlm aHagagezeards

?? Go under the house through the crawl space, to

see if there are any cripple walls.

?? If there are cripple walls, check to see if they

are braced.

?? There should be plywood panels adequately

nailed to the studs OR there should be diagonal

wood sheathing. (See Figure 16)

?? If you have neither of these, the cripple walls

are probably insufficiently braced or unbraced.

?? Horizontal or vertical wood siding is not

strong enough to brace cripple walls.

Remember

?? It is very expensive to lift a house, repair

the cripple wall, and put it back on its

foundation

Weak Cripple Walls

Figure 15 - Damage to home due to cripple

wall failure.

16 The Homeowner’s Guide to Earthquake Safety

Figure 16 - Diagonal Sheathing. Common in older homes.

Office of Emergency Services

Floor

joists

First floor

Cripple wall

Diagonal

sheathing

Comparison of Cost: Preventing vs. Repairing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

HOW-TO

The Solution

Plywood, or other wood products allowed by code,

should be nailed to the studs.

The following are important:

?? Type of wood product used

?? Plywood thickness

?? Nail size and spacing

?? Do not cover vents.

Consult your local Building Department for permit

requirements before starting work.

Strengthen Cripple Walls

The Homeowner’s Guide to Earthquake Safety 17

$500 to $2,500 $25,000 to total value of home (if completely destroyed).

First floor

Studs

Foundation

Floor joists Plywood panels

Nails at

appropriate

intervals

Anchor bolts at

appropriate intervals

Blocking

Vent holes

Siding

Cripple

wall

How-to Resources

?? Detailed information for do-it-yourselfers or

engineers can be found in the International

Existing Building Code, published by the

International Code Council

?? Publication: How You Can Strengthen Your

Home for the Next Big Earthquake in the Los

Angeles Area, City of Los Angeles,

Department of Building & Safety, October

2001.

2x4 Stud

Double

top plate

Siding

Anchor

bolt

Sill plate

Plywood

Nails at

appropriate

intervals

Figure 17—Plywood or

diagonal sheathing

strengthens weak cripple

walls. If your home has a

cripple wall between the

foundation and the first

floor, and the wall is not

braced with plywood or

diagonal sheathing, the

house may fall or shift off

its foundation during an

earthquake.

The outside of the house is supported by wood

posts resting on unconnected concrete piers.

Siding is often nailed to the outside of the posts,

making them not easily visible.

During an earthquake these posts can fail, if they

are not braced against swaying.

If the posts fail, the house may shift or fall.

California Seismic Safety Commission

?? Go under the house to see if there is a

continuous foundation under the outside walls.

?? If you do not see a continuous foundation you

may have an earthquake weakness.

??If you see only unconnected concrete piers and

wood posts, or only wood posts, supporting the

outside walls, you have an earthquake

weakness.

Remember

?? Horizontal or vertical wood siding is not strong

enough to brace pier-and-post foundations.

?? Major structural repairs, like lifting an entire

house to repair the posts and putting it back,

are very expensive.

Pier-and-Post Foundations

18 The Homeowner’s Guide to Earthquake Safety

Figure 18 - The pier-and-post

foundation under this home shifted

during a recent earthquake.

California Seismic Safety Commission

Comparison of Cost: Preventing vs. Repairing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

HOW-TO

The Solution

Consult a licensed architect or engineer, and a

licensed building contractor who specializes in

foundations, to fix this problem.

It may be possible to make the foundation safer by

bracing the posts.

You might be better off to add a new foundation and

plywood walls in the crawl space to make sure that

the house will not shift or fall off its foundation

during an earthquake.

?? Detailed information for engineers can be found in

the International Existing Building Code, published

by the International Code Council.

NCCoonnttseetnnruttssc tDDuaaramml aaHggaeezards

Strengthen Pier-and-Post Foundations

The Homeowner’s Guide to Earthquake Safety 19

$1,000 to $25,000 $20,000 to total value of home (if completely destroyed).

Unreinforced masonry—brick, concrete block, or

stone—foundations often cannot resist earthquake

shaking. They may break apart, or be too weak to

hold anchor bolts. Homes may shift off such

foundations during earthquakes, damaging the

walls, floors, utility lines, and home contents.

California Seismic Safety Commission California Seismic Safety Commission

Comparison of Cost: Preventing vs. Repairing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

HOW-TO

The Solution

?? If your home’s foundation is brick or stone, and

looks like one of the foundations shown in the

photos here, it is probably unreinforced.

?? If there is a space filled with grout between the

inner and outer faces of a brick foundation

(where anchor bolts and reinforcing steel could

be installed), it may be reinforced.

?? If the outside of the foundation is covered, you

may have to look under the house to see the

type of foundation you have.

?? If you are not sure what to look for, seek the

services of a licensed engineer to determine if

your foundation is reinforced or not.

Remember

?? It is cheaper to do this before an earthquake

damages the house than after.

Figure 20 - Note the bricks exposed in this unreinforced

masonry foundation.

Figure 19 - This is an unreinforced stone foundation.

They typically fail during earthquakes.

Unreinforced Masonry Foundations

20 The Homeowner’s Guide to Earthquake Safety

There are several ways to fix this problem.

The most common approach is to replace all or

part of the existing foundation with a poured

reinforced concrete foundation.

Another solution is strengthening the unreinforced

brick or stone foundation, which is generally

expensive.

Seek the help of a licensed architect or engineer,

and a licensed foundation contractor or general

contractor.

SSNCCCCttooorrounnnuunctttsccteeeHtttteunnnruunOurtttrrtsssacaaWs ltllDDD u-DDDTaaaraaaaOmmmmmlm aaaHaaagggagggeeezeeeards

?? Detailed information for engineers can be found in

the International Existing Building Code, published

by the International Code Council.

Retrofit Masonry Foundations

The Homeowner’s Guide to Earthquake Safety 21

$15,000 to $50,000 $15,000 to total value of home (if completely destroyed).

Houses built on the sides of steep hills are often

set on exposed posts or columns, as shown in the

photographs.

The potentially hazardous conditions that are

unique to homes on steep hillsides are:

?? Stilt-type posts with or without diagonal

bracing

?? Walls with very different heights or that are

stepped or sloped down the hillsides.

If these posts or walls are not properly braced,

they may collapse during an earthquake.

Sometimes, the supports on the downhill side will

be hidden behind a tall wall that encloses a large

unfinished space. (This is similar to, but taller

than, a crawl space under a typical house built on

flat ground.)

Office of Emergency Services

Office of Emergency Services

Comparison of Cost: Preventing vs. Repairing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

HOW-TO

The Solution

?? Is the house located on a slope?

?? Are the columns or walls supporting the home

braced?

?? If you are not sure if there is bracing or if the

bracing is adequate, consult a licensed

engineer.

Remember

?? It is very expensive to lift a house, repair the

posts, and put it back.

Homes Built on Steep Hillsides

22 The Homeowner’s Guide to Earthquake Safety

Figure 22 - This hillside home was built on an

unbraced tall wall that failed.

Figure 23 - This photograph shows an interior detail of a

home similar to the one above, showing substantial damage

to a building with an unbraced tall wall.

Consult a licensed architect or engineer, and a

licensed contractor, to fix this problem.

How-to Resources

?? Detailed information can be found in the

International Existing Building Code, published by

the International Code Council.

?? Voluntary Earthquake Hazard Reduction in Existing

Hillside Buildings, City of Los Angeles Municipal

Code, Chapter IX, Article 1, Division 94.

Strengthen Homes on Steep Hillside

Figure 24 - Hillside homes with sloped and tall walls or posts

require special engineering.

The Homeowner’s Guide to Earthquake Safety 23

$1,000 to $50,000 $10,000 to total value of home (if completely destroyed).

PEER and Nels Roselund, SE Sloped or

stepped

wall Tall

wall

Houses built of unreinforced masonry – bricks,

hollow clay tiles, stone, concrete blocks, or adobe

– are very likely to be damaged during

earthquakes.

The mortar holding the masonry together is

generally not strong enough to resist earthquake

forces.

Anchorage of walls to the floor and the roof is

critical.

These houses are weak (brittle) and can break

apart.

Walls may fall away or buckle, resulting in

damage.

California Seismic Safety Commission

?? Can bricks or stone be seen from the outside

(unless the walls are covered with stucco)?

?? Do the brick walls have “header courses” of

bricks turned endways every five or six rows?

(See Figure 26)

?? Was the house built before 1940?

If you cannot tell from the outside, turn off the

power and take the cover plate off one of the

electrical outlet boxes on an outside wall and look

for brick or other masonry.

If the wall is concrete or concrete block, it is very

difficult to find out if reinforcing steel was added

during construction.

You will then need:

?? The house’s plans, which may be on file with

the Building Department, or

Unreinforced Masonry Walls

24 The Homeowner’s Guide to Earthquake Safety

Figure 26 - Header courses

of bricks are usually placed

endwise every six or so rows

in unreinforced masonry

walls to tie the outer layer of

bricks to the layers inside the

wall.

?? To consult a licensed engineer to make

the determination.

Remember

?? It is very expensive to shore up a house,

remove damaged walls, and put in new

walls.

Figure 25 - The plaster-covered brick walls of this

building collapsed during a recent earthquake.

California Seismic Safety Commission

Comparison of Cost: Preventing vs. Repairing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

HOW-TO

The Solution

Consult a licensed architect or engineer to fix this

problem.

One solution may involve:

?? Tying the walls to the floor and roof

?? Installing a steel frame and bolting the

wall to it.

?? Detailed information can be found in the International

Existing Building Code, published by the

International Code Council.

Strengthen Unreinforced Masonry Walls

The Homeowner’s Guide to Earthquake Safety 25

Project and Repair costs can vary widely.

Figure 27 - Unreinforced masonry wall strengthened by

installing a steel frame inside.

Jessica Tran

Figure 28 - Bolting of unreinforced masonry wall to steel

frame on the inside.

Jessica Tran

IDENTIFY

WEAKNESSES

House

Garage

The Problem

The large opening of a garage door and the weight

of a second-story room built over the garage can

result in the walls being too weak to withstand

earthquake shaking.

When the narrow sections of the wall on each side

of the opening are not reinforced or braced, the

weakness is worse.

Comparison of Cost: Preventing vs. Repairing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

HOW-TO

The Solution

?? Is the garage door opening in line with the rest of

the house? (See Figure 30)

?? If this is the case, additional bracing may not

be needed.

?? Is the house shaped like Figure 31? If this is the

case, are there braces or plywood panels around

the garage door opening?

?? If there are no braces or plywood panels,

strengthening may be needed.

?? Consult a licensed architect or engineer to

determine the strengthening required.

Remember

?? Many homes with this weakness have been

severely damaged in past earthquakes.

Rooms over Garages

26 The Homeowner’s Guide to Earthquake Safety

HOUSE VIEWED FROM ABOVE

Figure 30 - If the wall of the main house is in line

with the wall containing the door of a garage with a

room over it, the adjoining wall may help brace the

garage.

Garage House

Figure 31—Additional bracing. Home configuration

where there is no in-line wall. Additional bracing may

be appropriate in this situation.

Garage

with room

above

HOUSE VIEWED FROM ABOVE

Figure 29 - This mountain home was built over a garage, and

its walls were not strong enough to withstand an earthquake.

Office of Emergency Services

Wall may need bracing

Consult a licensed architect or engineer to design

plywood paneling or a steel frame around the door

opening (See Figure 32).

Have plans drawn.

Obtain a permit from your local Building

Department.

Strengthen Rooms over Garages

Figure 32—Bracing garage walls. If your house has a

room over the garage, the garage walls may not be strong

enough to hold up during an earthquake unless they are

braced with plywood panels and steel straps.

The Homeowner’s Guide to Earthquake Safety 27

$5,000 to $25,000 $15,000 to total value of home (if completely destroyed).

?? Detailed information can be found in the International

Existing Building Code, published by the

International Code Council.

Plywood

panels

Steel straps

Anchor Bolts and Tie Downs

The Problem

Many chimneys are built of unreinforced brick or

stone. During an earthquake these can collapse

or break and fall on the roof.

When the chimney fails, the falling stones and

bricks can:

?? Cause injuries

?? Damage the house

?? Damage cars

Tall slender chimneys are most vulnerable.

OTHER EARTHQUAKE-RELATED

CONCERNS

?? Check the mortar between the bricks or stones

with a screwdriver. If it crumbles when you pick

at it, the chimney may be a hazard.

?? Inspect the attic and floor spaces for metal ties

that should be holding the chimney to the

house.

?? Determining whether a chimney is susceptible

to earthquake damage is not always easy.

When in doubt, consult a licensed engineer or

contractor.

Remember

?? Do not locate patios, children’s play areas, or

parking spaces near a questionable chimney.

?? Tell family members to get away from

chimneys and fireplaces during earthquakes.

28 The Homeowner’s Guide to Earthquake Safety

OTHER Unreinforced Masonry Chimneys

CONCERNS

Figure 33 - This unreinforced chimney fell during a recent

earthquake.

Office of Emergency Services

Figure 34 - Morgan Hill Earthquake. Broken chimney fell on

roof.

Guna Selvaduray

The Solution

Tear down the old or damaged chimney and

replace with a newly constructed chimney.

Several steps can be taken to reduce the risk of

damage from falling chimneys, depending upon

the type of chimney you have. They include:

?? Add plywood panels at the roof or above the

ceiling joists to prevent the brick or stone from

falling into the house.

?? This can be done by layering plywood

above the ceiling, in the house’s attic, or

nailing plywood under the shingles when

reroofing.

?? Replace the upper chimney with metal flues.

?? Strengthen the existing chimney.

?? This can be a complicated process,

depending upon the construction and

height of the existing chimney.

Consult your local Building Department and obtain

necessary permits first.

California Seismic Safety Commission

?? Reconstruction and Replacement of Earthquake

Damaged Masonry Chimneys, City of Los Angeles,

Department of Building & Safety, Information

Bulletin #P/BC-2002-70.

The Homeowner’s Guide to Earthquake Safety 29

Figure 35 - Photo showing damaged chimney removed.

Note that the fireplace is now not functional.

Strengthen Masonry Chimneys OTHER

CONCERNS

$2,000 to $12,000 $15,000 to total value of home (if completely destroyed).

Comparison of Cost: Preventing vs. Reparing Earthquake Damage

Project Cost Cost to Repair after an Earthquake

OTHER

CONCERNS

No Foundation

The Problem Some older houses were built on wood beams laid directly on the ground,

without foundations. These houses may shift during earthquakes, causing

structural damage and breaking utility lines.

How to Identify Look under the house. If you see no concrete or masonry around the outside

walls, the house may lack a foundation.

What Can Be Done You may need to add a foundation to make the house earthquake resistant.

Just as when strengthening or replacing an unreinforced masonry foundation,

you will require the advice of a licensed architect, engineer, or foundation

contractor.

Old Concrete Foundation

The Problem Some older concrete foundations were made with sand or stone that interacted

chemically over time, and the concrete eventually crumbles and becomes too

soft to withstand earthquake forces.

How to Identify Inspect the foundation for large cracks in the concrete, concrete crumbling off

the foundation, or concrete crumbling when you pick at it with a screwdriver.

What Can Be Done You may need to replace some or all of the foundation. You should consult a

licensed foundation contractor or an engineer.

Foundations

30 The Homeowner’s Guide to Earthquake Safety

OTHER

CONCERNS

The Problem The design and construction features of some homes make them vulnerable to

earthquake damage, especially if these homes are not specifically designed and

built to resist earthquakes. Homes at risk are those with irregular shapes, large

windows (which can break in earthquakes and scatter shards of glass), more than

two stories, irregular walls, or porches and overhangs.

How to Identify Many homes with these features are strong enough to withstand earthquakes and it

is difficult to tell whether such homes need strengthening. If you have doubts about

one or more of these features in your home, or in a home you are planning to buy,

you should consult a licensed architect or engineer for an assessment.

What Can Be Done A professional can advise you on how to identify and fix earthquake weaknesses if

necessary. For example, large windows can be made safer by applying plastic film

on them.

The Homeowner’s Guide to Earthquake Safety 31

Homes with Unique Designs

The Problem

Natural gas piping and appliances can be damaged

during earthquakes, causing gas leaks.

If ignited, this can result in fires which can burn part

of, or, the entire house.

About one in four fires after an earthquake is related

to natural gas leaks.

Gas leaks after an earthquake are more likely if:

?? There are structural weaknesses

?? Gas appliances are not anchored

?? Flexible pipe connections are not used.

The primary concern is property loss from fire

damage.

The potential for life loss is limited since most single

family homes have several safe exits.