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LIABILITY
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CITY OF TIGARD '`\
*".- _ REVIEWED FOI ,C ODE COMP
C/ Approved: i"i VALIDITY OF PERMIT
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-./ BASED ON CONSTRUCTION
i" Permit#: �j�aQly� �d 2�� DOCUMENTS AND OTHER
0 Address: 0l{40 la AA,San � DATA SHALL NOT PREVENT
Suite #: — THE CODE OFFICIAL FROM
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REQUIRING THE CORRECTION
By: - Date: OF ERRORS.ORSC 105.4
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4 .411
.c* Residential Seismic Strengthening ,
Methods to Reduce Potential Earthquake Damage
rmum
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Portland and the surrounding communities are homes, buildings and utilities can reduce damage
and the dangers of serious injury or loss of life from
located in a seismically active region. an earthquake. Modified from
Although most Oregonians have not witnessed a www.oregongeology.org/sub/earthquakes/E0s.htm
large earthquake in this region, large earthquakes The City of Portland, Bureau of Development
zhave occurred in the past. The Cascadia Subduction Services has a program to help you make your
Zone lies off the Oregon and Washington coasts
.;., where two sections of the earth's crust (tectonic home more secure in our next earthquake.
. Li
plates) are colliding, with one plate sliding beneath
W O (subducting) the other. Subduction zones have y` t;;
zs, produced some of the most powerful earthquakes
ever recorded, often having magnitudes of 8 to �'f..
W O 9 or larger. The 2004 Great Sumatra-Andaman 4_
Nlc.--) (magnitude 9.1) earthquake occurred on a ;,, `"'""
subduction zone. Studies have found evidence that k 4 L
very large earthquakes have occurred repeatedly in - _
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zz
7, the past on the Cascadia Subduction Zone, most
s O recently in January, 1700. Scientists believe the --_.,., ,,,;
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I ,0- Cascadia Subduction Zone is likely to produce large
O S earthquakes in the future. Extensive damage to Purpose
...1 buildings as a result of strong and sustained ground
W shaking is expected in the Portland area in the event The strengthening methods described by this
,1r . of a Cascadia Subduction Zone earthquake. program are intended to reduce the likelihood
601 p of your home being severely damaged by being
0 rn displaced from its foundation or cripple walls in an
LL M Oregon also has many crustal faults. These faults earthquake, however these measures will not bring
O N typically occur in the earth's crust, at shallow an existing building up to current code.
'21-7 depths of 6 to 12 miles below the surface. The two
P m largest earthquakes in recent years in Oregon, the The information provided in this brochure and
WScotts Mills (magnitude 5.6) and the Klamath Falls accompanying standard plan is intended to provide
(magnitude 5.9 and magnitude 6.0) earthquakes of a prescriptive method for one, two and three story
1993 occurred on crustal faults. Recent geophysical
= O studies and subsurface investigations indicate the one and two family residential buildings if they meet
m N the following criteria:
• r presence of at least three crustal faults beneath
the Portland metropolitan area which could •One and two family dwellings
0.c2
p generate much more damaging crustal earthquakes •Buildingsnot over 3 stories in hei9 ht. In 3
of magnitude 6.5 or larger. Although crustal
� story buildings, cripple wall stud height shall be
vi W O earthquakes are not expected to be as large as maximum 14 inches.
ce ._ earthquakes on the Cascadia Subduction Zone, their
O shallow depth and close proximity to people and •Cripple walls not exceed 4 feet in height in one
, ru developed property could result in as much or more and two story buildings.
Q damage to structures. •Continuous concrete foundation around the
Z O entire building perimeter.
JEarthquakes are a natural occurrence caused by the •Foundation sub grade not steeper than 3
constant motion of the Earth's crust. This motion
i"' � horizontal to 1 vertical at any point.
CC N creates the buildup of pressure along faults which is
O < released in the form of an earthquake. Earthquakes You will need to hire an engineer or architect to
Q. . are sudden and without warning. Strong ground design improvements to buildings that do not meet
LL shaking can cause severe damage to buildings, all of the above listed criteria.
cracking walls, toppling chimneys or even shifting
a N buildings off their foundation. Older buildings and You will need to hire an engineer or architect when
1- o homes are especially at risk because they often you have special conditions like a stone or brick
VcA lack adequate anchorage to their foundation and foundation, poor quality concrete, cripple walls
were not designed to resist the shaking and move- more than four feet in height, or your home is built
ment expected from earthquakes today. Identify- without a continuous foundation or on a grade
ing potential hazards ahead of time, strengthening steeper than three horizontal to one vertical.
Residential Seismic Strengthening-Methods to Reduce Potential Earthquake Damage • 1
Common Construction Problems ...but earthquakes can damage
Many homes were built using older newer, anchored homes too
construction techniques which are .:• t Some wood frame homes built as
inadequate for the forces we now know g / ®lU �' recently as the 1970s were shaken off
earthquakes can cause; but, these older ■Met _.
homes can be reinforced easily and 1�' -.-- their foundations in recent earthquakes.
""^ ` ` Even though these modern homes were
inexpensively. bolted down, they failed because of
weak bracing materials on the cripple
Older homes are typical victims...
walls. The cripple wall is a short wall that
Many homes built prior to connects the foundation to the first floor
1960 were built without being of the house and encloses the "crawl space." Weak
av.
bolted to their foundations. bracing materials, like cement plaster (stucco) or
Without this anchorage, a wood siding, are not strong enough to survive the
large earthquake can move the force of moderate to strong earthquakes.
ground and the foundation right
out from under the house. Older The cripple wall must be braced with stronger
homes have been damaged materials like plywood. If not, the next earthquake
or destroyed in every major . '4 may damage the cripple wall and move your home
earthquake on the west coast. off its foundation, even if you've bolted it down.
II I 111141
low
What to look for
To check your home's earthquake fitness, all you need is a flashlight and a willingness to get a little bit dirty. The
place to start is in the crawl space underneath your home.
1 1 Is your house properly bolted down to its foundation?
The most important and cost effective step you can take to help prevent or
minimize earthquake damage to your home is to make sure it is adequately
connected to the foundation.
The wood that rests directly on the foundation is called the mud sill. Until
the 1950's, home builders often did not bolt the mud sill to the foundation.
This creates a serious structural weakness that can allow your home to
slide off its foundation during an earthquake. The mud sill should be bolted
4, . ,¢ �.. , at four to six-feet intervals and within one foot of every joint, but no closer
than nine inches to the
end of the board.
2 Do you need plywood on your cripple wall?
Weak cripple walls are the second most common structural
weakness resulting in damage from earthquakes. , {
Check to see if you have a cripple wall and if it is braced with
plywood. If the cripple wall is covered on the exterior with \�
only stucco or wood siding, it is not strong enough to resist
earthquakes. You will need to add plywood. The Bureau's Standard
Plan shows you how much.
3 Check for faulty materials in the concrete and the wood framing.
The foundation is a common area of structural weakness. When concrete foundations are porous or crumbly, they
will not provide adequate strength to resist earthquakes. Unreinforced brick or stone masonry may need to be
replaced or strengthened. An engineer or architect is required to design these types of repairs.
Check to see if there is insect damage or dry rot in the wood. You will need to replace or repair any faulty wood
before you can proceed. Hiring a pest control company and fixing water leaks may be required.
Bolting your mud sill to the foundation and adding plywood to the cripple walls are the two most cost-effective
2 • Residential Seismic Strengthening-Methods to Reduce Potential Earthquake Damage
4
ril*�4 � steps you can take to strengthen your home for earthquakes. Bolts secure your home's mud
t w sill to the concrete foundation. The mud sill should be anchored as specified on the Bureau's
�'. " Standard Plan.
Sheets of plywood nailed to the cripple walls help to prevent damage from shaking in this
weak area of your house. Cross-bracing within the framing is not enough.
4
it c Faulty materials such as rotten wood and porous concrete should be replaced. Risky
conditions in concrete include cracks wider than one-eighth inch, large voids, or
,\. "honeycomb" concrete. If the concrete chips or flakes when you poke it with a screwdriver,
it may be unsafe. NOTE: If you suspect faulty material, you may need the assistance of a
licensedb
engineer or architect to design a solution.
,
DO I NEED A BUILDING PERMIT? -
Yes. The building permit process protects your interests by providing build- kyr
ing inspection. Our knowledgeable and well-trained inspectors will check
the quality and quantity of the work. This helps you make sure the job is
done right. „ .ti ,:
You will also have a permanent record in the Bureau of Development
Services that the work was permitted and inspected. You should keep the
final inspection card for additional proof. 66,,,of \,
-,,,, .\. ,:. ,,,,-,:
. ,...„,...„
HOW DO I GET A BUILDING PERMIT?
The City of Portland wants to simplify your home earthquake strengthen-
ing project. As part of this comprehensive program, we have developed a sample plan and details that can be used
for "prescriptive” projects that are within the guidelines of this brochure. You can download a copy online at our
website: www.portlandoregon.gov/bds/53562. You will need the plan along with this brochure in order to create
the plan for your house.
• First, prepare your plan. Someone will need to crawl under your home to see what details your plan will use.
Refer to the sample plan to draw a plan to show the configuration and dimensions of your foundation. Then
select the applicable details that apply to your home, and indicate the details you will use by referencing them
on your foundation plan. Print out each detail, the general notes, and compile these with your foundation plan
to create a complete set of plans for permitting, installation and inspection purposes. j
•Second, bring your completed plan to the Development Services Center for review by our helpful and friendly
staff. We can answer any questions you have, and help you complete your plan.
•Third, pay a permit fee. The fee will cover our costs to review and approve your plans, inspect the work and
keep a permanent record of it.
The first step to take if you find your home does not have anchor bolts, or has too few, is to install them! Because
anchor bolts cost as little as several dollars each, the perimeter of the average size home can be bolted down by the
do-it-yourselfer for a minimal cost. To install them, follow the procedure below and on the Bureau's Standard Plan.
1 Measure and mark
When you can easily drill the hole in the concrete, the concrete strength is low. Use the adhesive type of anchor
when the concrete strength is low.
Mark the places for each bolt on the mud sill. Make the first mark between nine and twelve inches from the end of
any piece of mud sill and then mark every six feet for one-story and every four feet for two- or three-story homes.
Residential Seismic Strengthening-Methods to Reduce Potential Earthquake Damage • 3
r..
How to Bolt Your Home to Its Fo,e
Continue this pattern along all of the exterior foundation walls. Make sure you
mark each end of the mud sill at stepped foundations. A small investment Checklist
in bolts can prevent many thousands of dollars of earthquake damage and
possibly allow a homeowner to still live in their home after an earthquake. LI 1/2" or 5/8" diameter an-
chors with nuts and square
2 Drill the holes plate washers
Use the drill bit diameter specified by the anchor manufacturer. The hole in Ll Rotary hammer drill with a
the concrete will be the same diameter as the anchor for the expansion anchor 1/2" or 5/8" by 9" carbide
and slightly larger for the adhesive anchor. The hole must be deep enough to tip drill bit
exceed the minimum depth approved for the anchor, but at least 4 inches deep ❑ Adjustable wrench
for expansion anchors and six inches deep for adhesive anchors.
U Measuring tape
3 Clean the holes
U Torque wrench
Follow the manufacturer's instructions on how to clean out the hole. Holes for
adhesive anchors need careful cleaning. Some products require water cleaning LI Dust mask and
and others use only a blower and nylon brush. Holes for expansion anchors do goggles
not need to be cleaned if they can be drilled deeper than required. This allows Li Short-handled sledge ham-
the drilling dust to settle out of the way. mer for setting expansion
bolts
4 Install the expansion anchors
Respirator, air blower
Place the plate washer on the anchor and then thread the nut on the anchor.
Place this anchor assembly into the hole and hammer on the nut to drive the Nylon brush for adhesive
anchor into the hole. Hammer the anchor down until the nut stops at the plate anchors
washer on top of the mud sill. Now tighten the nut down on the plate washer
to connect your mud sill to the foundation. When you tighten the nut on an
installed expansion anchor, the anchor's other end expands to grip the concrete. You will feel it grab the foundation
as you tighten the nut. If the concrete breaks during tightening of the expansion anchor, the concrete strength is
low and you will need to use an adhesive anchor. When your concrete has enough strength, the expansion anchor is
easier and cheaper to install than the adhesive anchor.
Note: The City of Portland provides information on approved products for residential seismic strengthening at
www.portlandoregon,,govibds/article/578535.
Adhesive anchors require more care but are as strong as expansion anchors. Follow the manufacturer's directions
on how to clean the drilled hole and how to mix and place the chemical. Always use a fully-threaded rod in the hole.
Check for the hardening time and after the chemical has set, tighten the nut firmly with a wrench.
Note: Manufactures installation instructions must be followed for all anchors, whether expansion or adhesive type.
Stepped foundation
Bolts with
If your house is built on a hill or even a slight ,r Plate Washers
grade, you probably have some step-like
offsets in your foundation. On every step, the Minimum
mud sill must be bolted down at each end and p 2 Be
pee r Step
along its length.
Requirements:
• Minimum of 2 Bolts per Step
• Bolts with Plate Washers 14111111411141104%iti
* 9" Minimum 12" Maximum to end of Plate
CAUTION: An engineer or architect must
9"Minimum
prepare the construction plans for the 12"Maximum
strengthening of homes built on hills steeper to end of Plate
than three horizontal to one vertical because
there are additional anchorage requirements.
4• Residential Seismic Strengthening-Methods to Reduce Potential Earthquake Damage
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Retrofit foundation plates
Some floors are supported directly on the foundation without cripple walls. This makes anchoring the mud sill difficult
because of the lack of drilling space. Plates can be used to anchor your mud sill from the side. The plates attach to the
side of the mud sill with wood screws and anchor to the concrete with either expansion or adhesive anchors.
The mud sill must be predrilled before the lag or wood screws can be installed. This helps prevent splitting of the
wood. The Bureau's Standard Plan has more information on plates and proper installation methods. Be sure to use
the type and length of screw recommended by the plate manufacturer.
How to Stre 1 0 t . t
1 Plywood 2 Blocking
Figure out how much plywood you will need on each Frequently lumber has to be added in the crawlspace for
cripple wall and where it should be placed. Plywood the new wall bracing or to attach the floor to the cripple
coverage is based on the number of stories. Plywood wall wall. These lumber pieces are called blocking. They
bracing is required at each wall end and for 40 percent of provide nailing surfaces for the plywood and framing
the length for one-story anchors. The plywood braces the walls and the framing
CHECKLIST homes, 50 percent anchors connect the floor to the cripple wall or mud sill.
CI1/2" CDX five-ply for two-story homes,
p y ply and 80 percent for Cripple walls are usually built with studs that are four
wood (do not use shop- inches wide. The mud sill is usually six inches wide. This
grade plywood)
three-story homes. difference in width requires blocking to be added to the
Use sheets at least
Li 8-penny, 10 penny and four feet in length. An top of the mud sill. The blocking provides a nailing surface
16 penny common nails easy way to distribute for the plywood at the bottom of the sheet. Some floor
LI Drill the plywood is to put
one-third of the required
L I Saw length on each wall end , b
Li Hammer and the remaining one- 4
third at the center of
Nail gun the wall. For example, r "',
if you have a single- — n-
[_1 Measuring tape •'
story home with 60 feet
1, 1 Chalk linetiMil
of cripple wall on one �
_,I Dust mask and protec- side, at least 24 feet of _,.
tion for eyes and ears plywood is required for
that side. You can put
❑ Blocking lumber two eight-foot sheets members sit on top of mud sills or cripple walls without
of plywood on each end blocking between them. The lack of blocking can cause
[3woo
p y Framing anchors the floor members to fall over sideways in an earthquake.
and one eight-foot sheet
near the middle of the It also makes it difficult to connect the floor to the
wall. Or you can use six four-foot sheets evenly distributed cripple wall or mud sill. If the blocking is missing between
along the wall with one panel at each end. This second the floor members, it must be added to help put the
alternative will allow you to avoid any piping, chimneys or earthquake forces into the strengthened wall.
ventilation holes at the cripple wall.
Residential Seismic Strengthening-Methods to Reduce Potential Earthquake Damage • 5
1411iliki '
1 _
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, , soit .
Framing
Anchors ,
Ventilation
= ...,,,,:i r >+. Holes
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Cripple Walls
Plywood
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3 Framing anchors
Framing anchors are small sheet metal connectors used by hand. Sometimes small working areas make hand
to fasten wood members together. They are used to nailing difficult. Wood screws can also be used, See the
connect your floor framing to the newly strengthened Bureaus' Standard plan for more information.
foundation or cripple wall. Although the existing floor is Most of the strength of the wall bracing comes from the
connected with nails, these nails tend to rust and loosen nailing of the plywood. Make sure you use 8d common
over time. The nails may also be driven at an angle nails with full heads on them. Place the nails at four-inch
which is not as strong as nails driven straight in the spacing along all edges of the plywood sheets. The
framing anchors. The addition of framing anchors helps middle of the sheets can be nailed every twelve inches
to make sure the building is properly connected to the into the studs.
newly strengthened part.
Framing anchors are a minimum of four-and-one-half 5 Ventilation holes
inches long and use at least twelve 8d nails. They may With the plywood in place, drill two to three-inch
be attached at the top of the cripple wall or to newly ventilation holes in each sheet. These holes should be
added blocking. Framing anchors are not required when centered above any anchor bolts, between each set of
the plywood can attach directly to the floor members. studs, and one inch above the mud sill and two-and-
For detailed information see the Bureau's Standard Plan. one-half inches below the bottom of the top plate. The
Note: The City of Portland provides information on holes will provide ventilation and allow inspection of
approved products for residential seismic strengthening the cripple wall. Drill only one hole if the plywood sheet
at www.portlandoregon.gov/bds/article/578535. is less than 18 inches tall. If your wall has an exterior
ventilation screen, you should cut a hole in the plywood
4 Nailing opposite the screen and similar to it in size. Don't
Nailing into old wood can cause splitting. Sometimes forget to add blocking around this vent hole and nail the
you will need to pre-drill holes when nailing the added plywood edges four inches on center.
blocking. If you blunt the end of the nails before you
drive them, they will be less likely to split the wood.
Plywood nailing is usually done by contractors with nail
guns to speed up the work, but it can be done
6• Residential Seismic Strengthening-Methods to Reduce Potential Earthquake Damage
Seismic Q&A
Q What are the benefits of strengthening my home?
A Strengthened homes are safer to live in and easier to sell and insure. Contact your insurance agent about
other possible benefits and specific information regarding your insurance policy. Evidence from past
earthquakes in California has shown that strengthened homes stayed on their foundations in the same
neighborhoods where unstrengthened homes did not!
Q How much does seismic strengthening cost?
A The cost of the work varies. Some homes have cripple walls that need a lot of blocking while other homes do
not have cripple walls. Some homes have plenty of access to the work area while other homes have limited
access because of heating ducts or small access holes. The cost of the work will increase significantly if you
need to replace an unreinforced masonry foundation or have a lot of termite or fungus damage to the wood.
You will get an idea of the fair value of the work to be done by getting at least three different bids from
contractors.
A All of the work shown on the Bureau's Standard Plan can be done by a homeowner with basic carpentry
skills. However, most homeowners are using contractors who specialize in this type of work. We recommend
you consider your skills, available time and budget to decide.
Q How do I find a contractor, engineer or architect?
A Visit Web sites associated with the professions.
• Construction Contractors Board: www.oregon.gov/CCB
• Structural Engineers (SEAQ): www.seao.org
• Architects (AIA): a;iaportland.org
The Bureau of Development Services would like to acknowledge the City of Los Angeles,Department
of Building and Safety for its assistance and permission to reproduce certain materials for this program.
Residential Seismic Strengthening-Methods to Reduce Potential Earthquake Damage • 7
1
•
Helpful Info �
Bureau of Development Services Important Telephone Numbers
City of Portland, Oregon
1900 SW 4th Avenue, Portland, OR 97201 BDS main number 503-823-7300
www.portlandoregon.gov/bds DSC automated information line 503-823-7310
General Office Hours: Building code information 503-823-1456
Monday through Friday, 8:00 am to 5:00 pm Planning and Zoning information 503-823-7526
BDS main number: 503-823-7300 Permit information for electrical,
Permit Information is available at the following location: mechanical, plumbing, sewer and signs .503-823-7363
Development Services Center (First Floor) Permitting process and fee information 503-823-7357
For Hours Call 503-823-7310 Resources and records 503-823-7660
or visit www.portlandoregon.gov/bds BDS 24-hour inspection request line
Permitting Services (Second Floor) (requires IVR number and three-digit
For Hours Call 503-823-7310 inspection code) 503-823-7000
or visit www.portlandoregon.gov/bds Residential information for
one and two family dwellings 503-823-7388
For more information about seismic hazards in the City of Portland TTY 503-823-6868
Portland area and Pacific Northwest, visit: Multnomah County Taxation &Assessment 503-988-3326
• www.oregongeology.org Multnomah County Planning & Zoning 503-988-3043
• www.pnsn.org
For more detailed information regarding the bureau's hours
• www.crew.org of operation and available services;
Green Building Resources:
• www.portlandoregon.gov/bps/41481 Visit:our Web site q,
www.port'ando egon.gov/bds
Note: All information in this brochure is subject to change.
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8• Residential Seismic Strengthening-Methods to Reduce Potential Earthquake Damage
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