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Earthquake and Retrofit Terms Glossary

Common Earthquake and Seismic Retrofitting Terms

Adequately braced - Wood-framed cripple walls are considered to be adequately braced if they have been strengthened in accordance with the provisions of Chapter A3 of the California Existing Building Code.

Adhesive anchor - Adhesive anchors consist of a steel threaded rod or rebar and a chemical adhesive that are inserted into a hole that has been drilled into the concrete or masonry substrate. Adhesive anchors generally use epoxy adhesives.

Anchor bolt - Steel rod threaded on one end that is fixed in concrete (or masonry) to attach a structure to its foundation. (Anchor bolts in new construction are placed in concrete before it cures or hardens. Anchor bolts in existing construction are typically adhesive or expansion anchors).

Applicant - Someone who has applied to become a Participating Homeowner in a California Residential Mitigation Program (CRMP) grant program.

Application - The collection of information requested by the Earthquake Soft-Story program or the Earthquake Brace + Bolt program and submitted through the website by Homeowners as a requirement to be considered for participation in the program.

Bearing Wall - A partition (wall) that supports any vertical load in addition to its own weight.

Chapter A3 - Prescriptive provisions for seismic strengthening of cripple walls and sill plate anchorage of light, wood-frame residential buildings. May be used in the retrofit of the crawl space area of the Living Space Over Garage (LSOG) house.

CRMP - California Residential Mitigation Program (CRMP) is a joint-exercise-of-powers entity formed by its members: the California Earthquake Authority (CEA), a public instrumentality of the State of California, and the California Governor’s Office of Emergency Services (Cal OES). CRMP is a legally separate entity from its members.

Cement - A fine gray powder that produces a bonding paste when mixed with water.

Concrete - A combination of cement, sand, crushed rock, or gravel. It is used for foundations, slabs and sidewalks.

Continuous perimeter foundation - A foundation, typically constructed of concrete or masonry, that is continuous under the exterior walls of a dwelling.

Crawl space - A shallow, unfinished space beneath the first floor of a house without a basement. The crawl space allows ventilation of floor framing and access to pipes and ducts.

Cripple stud - A short stud that is used in a framed timber wall.

Cripple wall - A less than full height wood stud wall extending from the top of the foundation to the underside of the lowest floor framing.

Drywall - Also known as wallboard, gypsum board, plasterboard, and by the trade name SheetrockTM, a wall-surfacing material composed of sheets of gypsum plaster sandwiched between a low-grade backing paper and a smooth-finish front surface paper that can be painted.

Earthquake - The sudden movement of the Earth when two large pieces of the Earth's crust, called tectonic plates, suddenly slip is called an earthquake. The release of pressure causes shock waves to shake and roll on the Earth’s surface.

Earthquake Brace + Bolt Program - Also known as EBB, this CRMP incentive grant program was developed to help homeowners lessen the potential for earthquake damage to their house from a raised foundation vulnerability. EBB offers grants of up to $3,000 for California homeowners to bolt, or brace and bolt, their house to the raised foundation.

Earthquake Soft-Story Program - Also known as ESS, this CRMP incentive grant program was developed to help homeowners lessen the potential for damage to their house during an earthquake from the Living Space Over Garage ("soft story") vulnerability. ESS offers earthquake retrofit grants of up to $13,000 for California homeowners to strengthen their garage, such as by installing plywood sheathing or steel panels on each side of the garage door.

Engineered solution - In the event a retrofit requires an engineer for calculations and/or plans, all designs must meet or exceed the requirements of FEMA P-1100 (PDF) for Earthquake Soft-Story (ESS) retrofits, or California Existing Building Code (CEBC), Chapter A3 for Earthquake Brace + Bolt (EBB) retrofits.

Expansion anchor (wedge anchor) - A type of anchor that is designed to expand inside the drilled hole in which it is placed; thereby securing itself by the resulting pressure and friction against the sides of the hole.

FEMA P-1100 - The pre-standard, presented as Volume 1 in the FEMA P-1100 product series, is supported by two additional volumes, currently under development. Volume 2 includes the FEMA Plan Set, a prescriptive, pre-engineered set of plans that can be adapted to retrofit crawlspace dwelling cripple walls and living-space-over-garage dwelling ground story bracing walls. Volume 3 consists of a series of products assembled to assist engineers in understanding the technical basis of the pre-standard.

FEMA-funded ESS program - The Earthquake Soft-Story retrofit grant program (ESS) is funded by grants from the Federal Emergency Management Agency (FEMA).

Foundation - The part of a building or wall which supports the superstructure. Typically made of concrete or masonry in residential construction.

Foundation plate - Used when there is not adequate vertical clearance under a house to properly anchor the mudsill to the foundation with conventional anchor bolts.

Framing clip - A device used to connect wood framing members. Typically used to connect bearing walls to floors and to the roof in residential construction.

General contractor - The contractor with main responsibility for the construction, improvement, or renovation project under contract, and is the party signing the prime construction contract for the project.

House - A single-family residential building (one to four dwelling units) meeting the requirements of Section 1.6 of the ESS Program Rules.

Joist - A framing member that supports a floor or ceiling load in a series of parallel members. Typically a 2x8 (2" by 8") or 2x10 (2" by 10") in residential construction. Lumber sizes are "nominal;" the actual finished lumber size will be less than the size indicated.

LA City Standard Plan No. 1 - A standard plan set available to homeowners and contractors for use as the construction document for the seismic retrofit of a wood frame dwelling. LA City Standard Plan #1, is in accordance with Chapter A3 of the CEBC and is available for download on the Los Angeles Department of Building and Safety website. Check with your local building department to see if they have adopted LA City Standard Plan #1.

Lateral-force resisting system that relies on poles or columns embedded in the ground - Some dwellings are supported on poles or columns embedded in the ground or supported on concrete piers and do not have any perimeter bearing walls. Without walls below the exterior walls of the dwelling, these supporting poles and columns will be required to act as lateral-force-resisting elements during an earthquake. Dwellings supported solely on poles and columns do not qualify for inclusion in the Earthquake Brace + Bolt program. (Poles or columns supporting decks or porches are not part of the lateral-force-resisting system provided there are walls or foundations below the exterior walls of the building.)

Low-slope site - A building site with a natural slope of 10 percent or less.

LSOG - Living space over garage. Also known as a "soft story."

Lumber - The product of the sawmill and planing mill by sawing, planing, cutting to length, and grading. 1" stock is sawed to 1" thickness then finished (planed) to final size of 3/4", 5/4" stock finishes out to 1" thickness, and 2" stock finishes out to 1 1/2". Lumber sizes are "nominal;" the actual finished lumber size will be less than the size indicated.

Magnitude - This is the measurement used to describe the total energy released in an earthquake. Scientists also use the moment magnitude scale, which measures the movement of rock along the fault, and accurately measures larger earthquakes, which can last for minutes and affect a much larger area.

Masonry - Building elements constructed of stone, brick, hollow clay tile, concrete blocks, gypsum blocks, or similar materials, or a combination of them.

Mudsill - The lowest sill of a structure. Typically supported by the foundation in residential construction.

Nominal dimension - The stated size of lumber, such as 2x4 (2" by 4"). Lumber sizes are "nominal;" the actual finished lumber size will be less than the size indicated.

Participating Contractor - A contractor who has registered with the California Residential Mitigation Program, and has successfully completed the Earthquake Soft Story (ESS) education module and requirements on the website. Participating Contractors are listed in the ESS Contractor Directory. Participating homeowners use this Directory to find a contractor to complete their ESS retrofit.

Participating Homeowner - An owner of a house who is participating in the Earthquake Soft-Story (ESS) grant retrofit program.

Plan Set A - A standard plan set, developed by the Association of Bay Area Government (ABAG), available to homeowners and contractors for use as the construction document for the seismic retrofit of a wood frame dwelling. "Plan Set A" (PDF) is in accordance with Chapter A3 of the California Existing Building Code and is available for download on the Association of Bay Area Government website. Check with your local building department to see if they have adopted Plan Set A.

Planing - The removal of the rough, or excess surface of a wood board.

Post - A timber member set on end to support a wall, beam, or other structural member. Typically a 4x4 (4" by 4") or 6x6 (6" by 6") in residential construction. Lumber sizes are "nominal;" the actual finished lumber size will be less than the size indicated.

Prescriptive standards - This prescriptive provision or plan set is a "blueprint" version of a prescriptive ("cookbook") standard for strengthening homes to better withstand earthquake shaking. When approved by the local building official, the plan set may be used to strengthen older homes without the need for costly site-specific plans and design calculations. This plan set provides a low-cost method to help improve an older home's chances of surviving an earthquake.

Qualifying Building - A single family dwelling with Living Space Over Garage (LSOG) vulnerabilities, typically one of four house types. See ESS Program Rules for more details.

Raised floor - A wood-framed floor that is supported or raised up off the ground by either wood-framing (such as a cripple wall) or a concrete foundation.

Raised foundation - A house with a raised foundation has an open area between the ground and the first floor (may be referred to as a crawl space). The raised foundation is created by there being short (less than full-story height), wood-framed walls and/or a concrete stem wall between the foundation and the wood-framed first floor.

Rules - The Program Rules for the Earthquake Soft-Story retrofit grant program.

Seismology - Seismology is the study of earthquakes. Scientists who study earthquakes are called Seismologists. When we talk about strengthening a house to make it stronger against earthquakes, it is referred to as a seismic retrofit because it is helping reinforce the house against the seismic waves and shaking of a damaging quake.

Seismic Waves - Earthquake waves travel through and on top of the surface of Earth causing the shaking and vibrations on the ground. Earthquake waves can move 20 times the speed of sound and can be felt a long way away from their point of origin.

Seismograph and the Richter Scale - When the earth trembles, a seismograph/seismometer measures the strength and duration of the earthquake and produces a graphic plotting the event. In the past, the Richter Scale was used to compare earthquakes, calculated in a ten-point scale. Scientists now use the moment magnitude scale, which measures the movement of rock along the fault.

Shear wall - A wall that has been designed and detailed to resist lateral (horizontal) loads on buildings. Often used in buildings to resist earthquake and wind loads.

Sheathing - The wooden covering on the exterior of walls and the roof. Typically made of 1/2" construction-grade plywood; older homes may have shiplap boards or planks.

Siding - The finish covering of the outside wall of a frame building. It may be made of horizontal weatherboards, vertical boards and battens, shingles, or other material.

Sill - Strong, horizontal wood member at the base of a stud wall. Typically, a 2x4 (2" by 4") or 2x6 (2" by 6") in residential construction. Lumber sizes are "nominal;" the actual finished lumber size will be less than the size indicated.

Sill Plate - A horizontal member, or board, laid directly on top of the foundation, to which the cripple wall, or first floor of the building, is connected.

Single-family detached dwelling - A free standing residential dwelling that is not structurally attached to a large, multi-family building. For the purposes of the Earthquake Soft-Story (ESS) retrofit grant program the dwelling may have one to four family living units.

Soft Story - A structure where the first floor is substantially weaker and more flexible than the stories above it due to large openings in the walls or very tall stories. This type of house typically requires an engineered solution due to cripple walls that are over 4 feet and/or wide garage door openings.

Soil liquefaction - The shaking from an earthquake can turn loose soil into a liquid during an earthquake.

Special Flood Hazard Area (SFHA) - As designated by FEMA, an area having special flood, mudflow or flood-related erosion hazards and is shown on a Flood Hazard Boundary Map (FHBM) or a Flood Insurance Rate Map (FIRM) Zone A, AO, A1-A30, AE, A99, AH, AR, AR/A, AR/AE, AR/AH, AR/AO, AR/A1-A30, V1-V30, VE or V. The SFHA is the area where the National Flood Insurance Program’s (NFIP’s) floodplain management regulations must be enforced and the area where mandatory purchase of flood insurance applies.

Standard Plan - A plan set that includes specifications, details, and instructions for the installation of foundation anchors and cripple wall bracing). These plan sets are intended for use without the services of a design professional (architect or engineer). Check with your local building department to see if they have adopted a standard plan for seismic retrofits.

Story - A story is a level part of a building usable by people for living or work, or both.

  • A roof (or a patio roof) is not considered a story.
  • An attic or attic space is considered a story if it has been remodeled for use as a room that can be used by people for living or work, or both.
  • A basement is defined as being beneath the main floor of a house, either completely or partially below ground. A full basement is considered a story.
All bi-level and tri-level houses are considered greater than one story.

Stud - Vertical member of a framed wall. Typically a 2x4 (2" by 4") or 2x6 (2" by 6") in residential construction. Lumber sizes are "nominal;" the actual finished lumber size will be less than the size indicated.

Subfloor - Boards or sheet material laid on joists and over which a finish floor is laid.

Tectonic Plates - Tectonic plates are large, thin layers of the Earth's crust. They stretch, move, slide and grind against each other. When the Earth’s upper mantle become stuck as the plates move past one another, the plates lock together, and pressure builds up. When they finally release, earthquakes occur. Many earthquakes happen on the edges of large sections of tectonic plates.

Tsunami - A giant ocean wave (or series of waves) created by an undersea earthquake, volcanic eruption or landslide.

Unreinforced masonry - A masonry structure that has no steel reinforcing bars embedded in it. The masonry blocks or bricks are connected by mortar.

Washer (Plate washer) - Square metal plates placed between the nut (head) of an anchor bolt and the wood mudsill. The washer acts to clamp the mudsill securely to the foundation. Note: It is now mandatory to use hot-dipped galvanized 3"x3"x1/4" square plate washers under the anchor bolt nut. Lumber sizes are "nominal;" the actual finished lumber size will be less than the size indicated.

For more about retrofitting and construction terms visit the Earthquake Brace + Bolt Program Glossary.

For more about the science of earthquakes and earthquake terms visit USGS Glossary.

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