Seismic Retrofit Training - Bia

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SEISMIC

.RETROFIT

TRAINING for Building Contractors & Building Inspectors

PARTIOPANT HANDBOOK

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ETTING STARTED

Why We Are Here ............................................................ 1

Now You KIlow ................................................................ 2

EARTHQUAKE BASICS

Factors Affecting Earthquake Forces ............................ 3

What is inertia force? ....................................................... 4

Two Structural Systems ................................................... 5

Cripple Walls .................................................................... 6

Effective Horizontal Force Resisting System ............... 7

Need for Seismic Retrofits .............................................. 8

Now You KIlow ................................................................ 9

SHEAR WALLS

Shear Walls Resist Two Forces ..................................... 10

Location of Shear Walls ........................................... ...... 11

Weak Story Crawl Space ............................................... 12

Tall-Narrow Shear Walls ............................................... 13

Typical Shear Wall ......................................................... 14

Evaluating Existing Sheathing ..................................... 15

Sheathing Checklist ....................................................... 16

Fastener Locations ................................................;,....... 17

Full Scale Nail Chart ..................................................... 18

Predrilled Holes for Nails ............................................ 19

Predrilled Holes for Standard Lag Screws ................ 20

Uplift Force in Holdown .............................................. 21

Holdown Installation Checklist ................................... 22

Now You KIlow .............................................................. 24

r--­

CONNECTIONS

')

Complete Load Path ...................................................... 26

Anchor Bolt End Distance ............................................ 27

Anchor Bolt Edge Distance .......................................... 28

Edge & End Distances (plan View) ............................. 29

Now You KIlow .............................................................. 30

FOUNDATIONS

Capping Existing Foundations .................................... 31

Now You KIlow .............................................................. 32

MISCELLANEOUS ELEMENTS

Now You KIlow .............................................................. 33

PROTECTING YOURSELF

Job Site Checklist ........................................................... 34

Now You KIlow .............................................................. 35

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Why We Are Here

Why Limit Our Focus to Residential Buildings? •

Large number of houses with weaknesses

•

Retrofit is simple to install

•

Larger buildings are more complicated

Training Objectives In this training, you willleam...

•

How earthquakes damage buildings

•

Key retrofit components

•

Installation Steps

•

How to avoid typical errors

•

Different materials available

•

Bracing techniques for nonstructural items

•

Protecting yourself

Seismic Retrofit Training - Participant Handbook v. 1- 2/95

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GEnlNG STARTED

Now You Know

1.

Our focus is on 1-4 unit wood frame houses, not commercial buildings, apartments, or mobile homes.

2.

There are literally thousands of buildings of this type that will need seismic retrofits in the immediate future.

3.

You can use the building department's pre­ scriptive standard to retrofit a house without an architect or engineer if the building meets the standard's strict requirements.

4.

Incorrect retrofit installations are as bad as having no retrofit at all.

5.

You are liable for damages that result from installation errors made by you.

Seismic Retrofit Training - Participant Handbook v. 1- 2/95

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EARTHQUAKE BASICS Factors Affecting Earthquake Forces

Soil Under Building

Earthquake Magnitude Distance from Epicenter

W

hen an earthquake strikes an area, the ground below each building shakes in all directions. The magnitude of shaking is not the sole factor that determines the amount of force felt by the building. The force will depend on the following factors: •

Magnitude of Earthquake - This is usually described by a number on the Richter scale.

•

Distance from Epicenter - Buildings that are closer to the epicenter will usually feel stronger shaking than buildings that are further away.

•

Soil Under Building - A building on hard, rocky ground will shake differently in comparison to one on soft clay soil.

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•

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What is Inertia force?

L

nertia forces act in the opposite direction of ground movement. The concept of inertia orces can be explained by the example of a person standing in a moving vehicle (as illustrated below).

t

Ace ele ration

• •

Deceleration (Braking)

When the vehicle starts or accelerates, the vehicle moves forward as the person inside feels an inertia force moving him backward. Similarly, when the vehicle stops or decelerates, the person feels an inertia force pushing him forward.

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EARTHQUAKE BASICS

Two Structural Systems

Gravity Force Resisting System

~~_~

Roof Joists

a..---Walls

t::====:;;;I---- Floor Beams ~--Foundations

Horizontal Force Resisting System

Roof Diaphragm Shear Wall

Foundation

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EARTHQUAKE BASICS Cripple Walls

it

M

any older houses have first floors supported on short walls called "cripple walls." They go around the perimeter of the house. These walls must also act as shear walls because these are the only walls at this level and they do not have sheathing on the inside face. Earthquake forces are also larger at the lowest levels of a house. Most of these existing perimeter cripple walls do not have the strength or the connections to act as shear walls. Therefore, the cripple walls are usually very vulnerable during an earthquake.

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EARTHQUAKE BASICS

Effective Horizontal Force Resisting System

Shear Wall Connection Shear Wall \---- Connection

1--- Foun dation

F

or the Horizontal Force Resisting System to be effective, ALL portions of the building must be connected together to allow the earthquake forces to transfer from the structural elements to the ground. This is called the "load path."

Structural failures occur when there are weaknesses in the elements or connections along this load path.

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---.----­

•

~~__---------------------E-A-RT-H-Q-U-A~K-E~B-A-S~IC~S ~ Need for Seismic Retrofits

Reasons for Retrofitting

•

Voluntary - Increase Value

- Safety

• •

Code Requirement

Insurance Requirement

Complete Seismic Retrofit •

Installing shear walls

•

Installing anchor bolts

•

Connecting shear walls to the building

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-~-"-"-"-.

--"­

EARTHQUAKE BASICS

Now You Know

The shaking felt by a house depends on the magnitude of earthquake, distance from the epicenter, and composition of soil between the house and the epicenter.

2.

Earthquakes cause inertia forces to act on a house in all directions.

3.

Buildings have both Gravity and Horizontal Force Resisting Systems.

4.

Cripple walls in older homes are not strong enough to withstand earthquake forces.

5.

Weak stories cause significant damage during an earthquake.

6.

Seismic retrofits consist of anchor bolts, shear walls, and connections that help to strengthen obvious weaknesses in older homes.

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SHEAR WALLS

Shear Walls Resist Two Forces

Shear Forces

• Upliff

Seismic Retrofit Training - Participant Handbook v. 1 - 2/95

Forc~s

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SHEAR WALLS Location of Shear Walls

Exterior

Shear Walls

Interior Shear Walls

Although a house has many walls, not all of them can act as shear walls. For a house to effectively resist earthquake forces, shear walls are required: •

In each story of a building and within the basement, garage, and crawl space

•

On all exterior sides of the building and at

some interior walls •

To be aligned vertically from the foundation to the roof if possible

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SHEAR WALLS Weak Story Crawl Space

Earthquake Force

Side Sway & Possible Collapse

k

house has a weak story if any of its stories does not have enough strength to resist arthquake forces. Floors, basements, garages, or spaces with few walls are considered weak or soft stories. To strengthen and stiffen a weak story, an engineer or architect may require additional shear walls with heavily nailed plywood sheathing, hold owns, and additional framing and hardware.

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•

SHEAR WALLS

Tall - Narrow Shear Walls

Earthquake Force , /~/~______________~~~

,.... f

r

-I--------.....~. . .

I I I

T

all and narrow shear walls behave differently than those that are short and long. A wall that is too narrow will usually be too flexible and may not have the required strength. Tall and narrow shear walls have a greater tendency to uplift because they are not as wide at the base. There is less weight on the wall to resist uplift. Consequently, limits are placed on wall height in relation to the length of a shear wall.

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Typical Shear Wall

Tap Plate(s) ""\

Panel Edges

End Stud

Siilor~

Sole: Plate:

Y

'Window Ope:ning

add the following components to conventionally framed stud walls to form shear walls:

OU

•

Sheathing (consisting primarily of large pieces of plywood)

•

Fasteners

•

Additional framing (end posts, blocking)

•

Holdowns (depending on forces calculated by an engineer or architect)

Seismic Retrofit Training - Participant Handbook v. 1- 2/95

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SHEAR WALLS Evaluating Existing Sheathing

Type

Structural

Plywood

Wood

Gypsum

Board

Is each piece of sheathing... 1.

Properly nailed along its edges?

2.

Properly nailed to the end studs, top plate, & sill or sole plate?

3.

Properly nailed to intermediate studs?

Laid diagonally across face of stud wall, it's acceptable if... 1.

Each board extends from top plate to sill or sole plate.

2.

Boards nailed to each stud they cross AND nailed to top & bottom plates.

Is each sheet... 1.

Adequately fastened along edges of each panel?

2.

Adequately nailed to: End Studs Top Plate of Double Top Plate Sill Plate or Sole Plate

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Materials

(Asl Yourself

Sheathing Checklist

Trle~e Que~tlcn:;J

1. Is the specified sheathing 5-ply ply­ wood? This is the recommended sheathing for strengthening wood frame houses. 2.

Does each plywood panels grade stamp match the "specified" grade?

3.

How long is the wall? Longer walls are stronger than narrow ones.

4.

Did you combine sheathing materials? As a rule, don't combine different materials on the same wall.

5. Do you need to install gypsum board over new sheathing for fire protection?

Fasteners o

(Things to Rememr)er)

Follow the spedfications on the supplied plans.

o

Don't drive lag screws; you must screw them.

o

Nails should have flush heads.

o

Don't overdrive nails.

o

Don't drive nails near the edge of sheathing.

o

Use correct fastener as spedfied by the contract.

o

Don't use screws/ staples unless specified.

o

Don't apply coating to fasteners prior to installation.

a

Predrill fastener holes if there is a potential for splitting.

Seismic Retrofit Training - Participant Handbook v. 1- 2/95

Hardware

(Warnings!)

Do NOT ... use hardware from a manufacturer that is not approved by the building official and engineer or architect!

Do NOT ... substitute lag screws for bolts!

Do NOT... use fasteners that don't match exactly the manufacturer's specifications!

Stud Wall Without Sheathing Earth quake Force

..-.i"

I+- Excessive I· Side Sway

- - - - . r --- ~-r-'T""'Ir--r-.-~--i

I

I

I

I

I

I

Stud Wall With Sheathing Eartfl quake Force

ControUed Sidesway

...- - Resists Earthquake Force

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SHEAR WALLS

Fastener Locations

Edge Nail Top Plate Nail Intermediate Studs Edge Nail Common Studs Typical Sheathing Edge Nail To Blocking Around Opening Edge Nail End Stud & Holdown Stud Edge Nail Sale ' - - ­ Or Sill Plate

E

addition to using the correct size nail, you must be sure to install them correctly. Due in art to the shear volume of nails required in plywood sheathing, you will usually use a nail gun. If you nail too closely to the edge of the sheathing, the nails may prematurely split the sheathing when resisting earthquake loads.

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SHEAR WALLS Full Scale Nail Chart

Wire Diameter

Wire Gauge

Length

20d

.192

6

4

16d

.162

8

31/2

12d

.148

9

31/4

lOd

.148

9

3

8d

.131

101/4

21/2

6d

.113

111/2

2

20d

.148

9

4

16d

.135

10

31/2

12d

.128

101/2

31/4

lOd

.128

101/2

3

8d

.113

111/2

21/2

6d

.099

121/2

2

16d

.148

9

31/4

8d

.113

111/2

23/8

lOd

.148

9

11/2

8d

.131

101/4

11/2

Green Vinyl Sinkers

Joist Hanger

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Predrilled Holes for Nails

(less than 75% of nail diameter)

PREDRILL HOLE SIZE COMMON

2Dd

1/8"

16d

1/8"

12d

3/32"

10d

3/32"

8d

3/32"

6d

1/16"

20d

3/32"

16d

3/32"

12d

3/32"

10d

3/32"

8d

1/16"

6d

1/16"

BOX

GREEN VINYL SINKERS

16d

3/32"

8d

1/16"

JOIST HANGERS

lOd

3/32"

8d

3/32"

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SHEAR WALLS Predrilled Holes for Standard Lag Screws

PREORILLED HOLES FOR STANDARD LAG SCREWS O:~~~~- TREAD ED DIAMETER (0 T)

LENGTH OF SHANK ( L S )

TREAD ED PORTION (L T )

PREDRILL HOLE SIZE

SCREW

SHANK DIAMETER

THREAD DIAMETER

3/4"

3/4"

1/2"

5/8"

5/8"

7 /16"

1/2"

1/2"

5/16"

7 /16"

7 /16"

1/4"

3/8"

*3/8"

3/16"

5/16"

*5/16"

5/32"

1/4"

*1/4"

1/8"

LAG

II-

Drilling of shank hole not required provided wood DOES

NOT SPLIT.

PROCEDURE:

1. 2.

Drill thread diameter (DT) to a depth equal to length of lag screw (LT + Ls)' Drill shank diameter (Ds) to a depth equal to shank length (Ls)' Do NOT over drill shank diameter.

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SHEAR WALLS Uplift Force in Holdown

Shear Force --~.... =====--=== =======--

--------­ ---------

I

C Shear Force

Tension In Holdo'Nn Rod

E

arthquake forces acting on the top of the shear wall not only create shear forces in the wall but also uplift forces at the ends of the wall. These forces tend to lift up one end of the wall and push the other end of the wall down. In some extreme cases, the uplift forces can even tip the wall over. Usually, there will be some gravity load pushing down on the wall to resist some of the uplift. The amount of gravity load resisting uplift varies depending on the length of the wall and the framing of the floor or roof above the wall.

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SHEAR WALLS Holdown Installation Checklist

HOLDOWN INSTALLATION CHECKLIST

SHEAR IO'ALL

\ \

FOUNDATION " - HOLOO\I\IN ROC. TlGIfTEN SNUG AFTER TIGHTENING SOLTS TO STUD OR POST

IILOCI(JNG OR JOIST UNDER END SnJD OR HOLDOWN POST

CHECKLIST D Holdown post is correct size.

D Holdowns are correct size. D Holdown bolts are correct size & length. D Holdown rod is correct size & length.

o Nuts & washers are correct size & length. o End studs or holdown posts are bearing on sill or sole plate. D Hole drilled into foundation is the correct

diameter & depth. D Hold is cleaned of all dust & debris before the rod is epoxy grouted into place. D The first bolt hole is drilled the required

distance from the end of the end stud or post per holdown manufacturer. Seismic Retrofit Training - Participant Handbook v. 1- 2/95

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SHEAR WALLS Holdown Installation Checklist (cont.)

D The bolt holes are drilled the proper size (not greater than 1/16" larger than bolt diameter). D Bolts in end stud or holdown post should

not be countersunk. Route out adjacent framing to accommodate heads of bolt, but do not outer cut existing framing. D Bolts are tightened to stud. D Holdown threaded rod is an adequate length

to extend from bottom of hole to holdown (or between holdowns). D Nuts & washers are used to fasten rod to holdown per manufacturer. Rod should be an adequate length for the nut & washer to be fully engaged on rod. D Holdown rods are tightened snugly.

D All framing shown on the drawings is installed.

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v. 1- 2/95

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SHEAR WALLS

Now You Know

1.

Shear walls are vertical elements of the hori­ zontal force resisting system.

2.

Shear walls provide lateral strength for re­ sisting horizontal earthquake forces and prevent the roof or floor above from swaying sideways.

3.

They resist both shear forces and uplift forces.

4.

Weak stories are floors, basements, or ga­ rages that only have a few shear walls or a number of short length shear walls.

5.

Tall and narrow shear walls have a greater tendency to uplift.

6.

Shear wall components include sheathing, fasteners, additional framing, and holdowns.

7.

Some existing sheathing can be considered effective if they pass certain requirements.

8.

Structural grade plywood (five-ply) is rec­ ommended for new sheathing.

9.

You should not combine the strength of two different sheathing materials as a rule.

10. Nails are the most typical type of fasteners used for shear wall installations; don't sub­ stitute screws and staples. Seismic Retrofit Training - Participant Handbook v. 1 - 2/95

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Now You Know (cont.)

11.

There are several ways to avoid splitting the framing when you nail.

12. Always follow the hardware manufacturer's catalog for installation details. 13. The sheathing is attached with fasteners to existing stud wall framing. 14. Blocking may be needed along any unsup­ ported edge. 15. An engineer may specify the addition of holdowns to the end studs of the shear wall to resist uplift forces. 16. Cripple walls often require sheathing and hardware installed in order to act as shear walls between the first floor and the founda­ tion. 17. Ventilation reduces the potential for wood decay in repaired or retrofit areas.

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CONNECTIONS

Complete Load Path

Top Connection

Roof Sheathing

Shear Wall

~~

Foundation

t---

~I----

Bottom Connection Top Connection Shear Wall

\ . - - Bottom Conn ection

T

he load path is like a chain; it is only as strong as its weakest link. When all of the elements above are connected, they form an unbroken path from the roof to the ground that will transfer the diaphragm loads. A similar path must be traced to the ground from each of the floors. 'Without proper connections, these elements will separate or slide past each other during an earthquake.

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CONNECTIONS

Anchor Bolt End Distance

7 bolt diameters Min 12 inch Max

7 bolt diameters Min 12 inch Max

T

he foundation sills must be attached to the foundation with anchor bolts well­ embedded into the concrete. The codes require every piece of foundation sill to have at least two anchor bolts (every piece must have a bolt within 12 inches of each end). Anchor bolts should be installed and tightened before the blocking is installed.

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Anchor Bolt Edge Distance

Stud Anchor Bolt

Plate wash er Foundation Sill Foundation - _ _~

Sill Edge Distance Foundation Edge Distance - - - 1 - - - 1

N

nchor bolts should be installed near the center of the foundation sill to maintain dge distance. These bolts also need adequate edge distance to the side of the concrete to avoid blowing it out. Check with the manufacturer to get the minimum side cover on the bolts. When drilling the holes for anchor bolts, it will sometimes be necessary to drill at a slight angle because of access problems. Make sure the bottom of the hole has the proper side edge distance.

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.. CONNECTIONS

Edge & End Distances (Plan View)

•

Foundation Sill Plates

Edge Distance

~ End Distance

END DISTANCE BOLT SIZE

EDGE DISTANCE

1/2"

3/4"

3-1/2"

12"

4"

5/8"

15/16"

4-3/8"

12"

4"

3/4"

1-1/8"

5-1/4"

12"

6"

MINIMUM MAXIMUM

SILL WIDTH

NOTE: Some engineers or building departments may require larger minimum end distances.

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~~-~b ~

C_O~N~N_EC~T~IO_N__S

___________________________

Now You Know

1.

The connective elements must be attached to each other in order to form a complete path for loads to be carried from the roof to the ground.

2.

Rotted wood cannot resist earthquake forces as well as undamaged wood.

3.

Use the same principles for creating load paths when retrofitting balloon-framed houses.

4.

You must attach foundation sills to the foundation with anchor bolts well­ embedded into the concrete.

5.

Always try to eliminate a moisture source before replacing rotted wood otherwise you cannot prevent future deterioration.

6.

Foundation sill cannot perform its function if the foundation is mislocated; you must notify the engineer or architect.

7.

Always use proper bolt sizes and lengths for both wedge and epoxy anchors.

8.

Protect yourself, your workers, and the owners from the epoxy fumes.

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FOUNDATIONS Capping Existing Foundations

New Sill Plate -.~~.!I!!!.II!!!!I!!~ & Anchor Bolts !!'.'!

. __

Concrete Cap

Existing Brick

Foundation

C

apping of the foundation involves adding concrete along the top of the existing footing and along the sides. Capping may be needed if the existing footing is not strong enough to resist the forces of the anchor bolts. The concrete cap would help to insure that the anchor bolts were embedded into good, strong material. Capping that extends down the sides may be specified when the new forces on the foundation are too great for the soil to resist. An extra width of concrete along the side of the existing foundation is used to spread out the forces on the soil.

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FOUNDATIONS

Now You Know 1.

Foundations transfer forces from the structural framing to the ground.

2.

Foundations resist both horizontal sliding shear force and uplift force.

3.

A shear wall requires a continuous foundation under its entire length.

4.

Some older houses don't have foundations; others have foundations consisting of posts and piers or perimeter footing with interior posts.

5.

Newer houses are constructed with a concrete slab cast on the ground.

6.

If an existing foundation has deteriorated, the materials will not have any strength to resist earthquake forces.

7.

You must beware of cracks found in a concrete foundation; have an engineer inspect them before installing a retrofit.

8.

Foundation must be embedded into the ground.

9.

There are only a few instances when you should disturb the soil around a foundation.

10. The two basic methods of retrofitting a foundation are capping and replacement. Seismic Retrofit Training - Participant Handbook v. 1- 2/95

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1":.

~~-~__________________~IS_C_EL_L_A_N7EO~US~E_LE~M~E_N __ __ TS

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Now You Know

t

Brick chimneys in older homes are highly susceptible to earthquake forces; don't take the responsibility for recommending chimney bracing. Always defer to an engineer or architect.

2.

Straps and brackets keep posts from separating from the roof or floor deck, but they do NOT increase the strength.

3.

Automatic shutoff valves on gas lines help to prevent catastrophic fires.

4.

To prevent a water heater from overturning, brace at the top and base and use flexible connectors.

5.

Read FEMA's "Reducing the Risks of Nonstructural Damage: A Practical Approach" for more information on bracing nonstructural items.

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PROTECTING

VOURSELF

Job Site Checklist

Safety on the Job Site o

Use a respirator whenever there are airborne particles.

o

Always wear hardhats.

o

Rope off dangerous areas.

o

Do NOT design the shoring yourself.

Documentation

o

Obtain a written contract

o o o

Obtain a set of plans with drawings. Do a preconstruction walkthrough before bidding on the work

o

Take photographs of existing conditions.

o

Outline your responsibility - notify owner of existing conditions.

o o

Document any change orders. Identify need and schedule for inspections - arrange them.

o

Document and show all problems to engineer or architect

o o

Keep record of all inspections.

Secure a building permit

Take photographs of all completed work

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PROTECTING YOURSELF

Now You Know

1.

Safety on the job site is important for both you and your employees.

2.

Always be aware of the various concerns of the home owner.

3.

Always document your work.

4.

Don't mislead the home owner into believing that the house is "earthquake proof."

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