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Earthquake Seismic Retrofit

Seismic Retrofit Contractor

Seismic Earthquake Foundation Retrofit Contractor Located in Castro Valley, Serving the San Francisco Bay Area

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Why Should I Retrofit My Home?

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A home that has been retrofitted is able to resist much greater earthquake forces and has a lower risk of being damaged.

During an earthquake, the strength of a home is put to the test. Ground forces try to tear the home apart and in many cases, cause severe damage. If you live in an area prone to earthquakes, it’s important that the structural frame of your home is strong enough to absorb an earthquake’s energy .

Advances In Engineering

Fortunately, advances in structural engineering, lessons learned from past earthquakes and research performed by the scientific community have paved the way for the development of new construction techniques that better equip homes to withstand an earthquake. Local and regional building codes now require all new homes to meet these higher construction and safety standards.

Older Building Codes

Failed Residence Without Proper Retrofitting

Since many existing homes were constructed prior to the development of these newer code requirements, a retrofit may be necessary to increase structural safety. A retrofit adds bracing and reinforcement to strengthen the critical connections within a home. A home that has been retrofitted is able to resist much greater earthquake forces and has a lower risk of being damaged. Upgrading a home to the latest building code standards, however, is not always practical for most older homes. This type of upgrade would require structural engineering and significant/invasive construction modifications. This evaluation would include the removal of many finish materials, such as sheetrock, stucco, siding, etc., to examine the construction of the home.

New Less Intrusive Retrofit Methods

Fortunately, there are less intrusive ways to retrofit older homes and improve their structural safety and performance during an earthquake. We provide product solutions that increase the strength and safety of homes. These products are used to connect and secure the structural frame of a house. Most of our retrofit products are manufactured by Simpson.

Simpson Research Lab

In 2003, Simpson opened a research laboratory to better understand how earthquakes, high winds and other natural disasters affect building performance. The lab’s state-of-the-art testing equipment can recreate the magnitude of such earthquakes as the 1989 Loma Prieta quake in California, which measured 6.9 on the Richter scale. The testing and research being conducted is helping to advance product development and improve building design and safety. Golden Gate Enterprises, Inc. can help you protect your home using the latest techniques and equipment.

Reasons To Retrofit

Your home will have a better chance of surviving the next big earthquake and with less property damage and loss of life.
Retrofitting your home may lower earthquake insurance premiums and deductibles.
Strengthening your home can add resale value.

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Earthquake Basics

Before you begin a retrofit project, it’s important that you are familiar with the basic principles of home construction and how earthquakes impact your home.

Earthquake Basics: Lateral and Uplift Forces

During an earthquake, a home experiences two types of forces: lateral forces and uplift forces. Lateral (or shear) forces are horizontal forces that result in back and forth (side to side) movement, also known as racking. Lateral forces can shake the house and weaken its frame and cause it to slide off the foundation. Uplift forces are vertical forces that result in up and down movement. Uplift forces can cause the house tooverturn and lift off the foundation. Using a continuous load path throughout the home strengthens the entire structure and helps it to resist lateral and uplift forces.

Earthquake Basics: Continuous Load Path

Building codes now require homes to meet higher structural design standards, including the use of a “continuous load path.” This method of construction involves creating a series of solid connections throughout the home. These connections are created by using a system of wood framing, metal connectors, fasteners (like nails and screws) and shearwalls. These connections are critical during an earthquake. A continuous load path redistributes external forces from an earthquake by transferring these forces from the frame of the house to the foundation. A home is more likely to withstand an earthquake and stay intact when each part of the house is connected together. In general, houses built within the last 20 years, should have been constructed with a continuous load path.

Do I Need To Retrofit My Home ?

There are certain types of homes that are more likely to need a retrofit than others. A quick analysis of your home can help determine if your home fits that criteria.

1. Am I living in an area prone to earthquakes?

There are geographic areas that are considered high seismic regions. These seismic areas are based on the likelihood of an earthquake occurring and its severity. The easiest way to find out if you are living in a high seismic area is to call your local building department and ask if you are in Seismic Zone 3 or 4 (for California residents) or Seismic Design Category D, E or F. These designations are assigned to regions with high seismic potential.

2. Was my home built within the last 20 years?

As a general rule of thumb, homes built within the last 20 years were designed to conform to stricter building codes and willbe better equipped to resist the force of an earthquake. Homes built prior to that timeframe are typically more vulnerable to earthquake damage.

3. Is my home built on a raised foundation?

If your house is not built directly on a concrete slab, chances are it’s built on a raised foundation. This means the home was built on a system of posts, beams and “cripple walls” (cripple walls are short wood-framed walls running underneath and around the perimeter of the house). These homes typically have crawl spaces underneath them. They are susceptible to damage because the supporting structure under the house may not have been built to resist seismic forces and thus is considered a weak area. Past earthquakes have shown these areas are highly suceptible to structural failures as shown in the illustration below.

4. Is my home built on a hillside?

Homes built on a hillside typically have raised foundations and crawl spaces as those described above and can experience similar failures. However, these failures tend to be more severe because the posts and cripple walls supporting the home are built at different heights due to the uneven terrain.

5. Is there living space above my garage?

Garages are vulnerable areas in a house due to the large garage door opening. Because of this large opening, the narrow walls on either side of the garage door must be designed to resist earthquake forces. This is extremely important if there is a living space above the garage because these rooms add weight that the garage must support. Current building codes require that these narrow walls be specially designed to resist earthquake forces. Older homes, however, typically did not address this issue and are more vulnerable to damage during an earthquake as shown in the illustration.

If you live in an older home with a living space above the garage or on a hillside, we will need to consult with our licensed structural engineer for design solutions.

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1. Is the top of the crawl space perimeter wall properly attached to the floor system?

On top of the crawl space wall rests the floor system. Around the outside of the floor system and the perimeter wall system is what is known as the rim joist. The rim joist should be attached to the top of the wall with metal connectors. The connectors should be located approximately 16 inches on center.

Cripple Wall To Floor Connections

2. Are the crawl space perimeter walls too tall?

In certain cases, an engineer must design your retrofit solution, these include:

• If your home is one or two stories and the perimeter wall height is greater than 4 feet at any point

• If your home is three stories and the perimeter wall height at any point is greater than 14 inches

• If your home is more than three stories

3. Are the interior columns attached properly to the beams they are supporting?

Often there are interior columns supporting the floor system . The tops of these columns should be attached to the floor beams with a metal connector.

4. Are the bottom plates of the crawl space perimeter walls properly attached to the foundation?

Building codes require that 5/8|-inch diameter anchor bolts should be placed at certain locations to prevent the home from sliding off of the foundation. According to the code, anchor bolts must be located within 12 inches from the end of each plate line and no more than 6 feet on center for one and two-story homes. The bolts should have a bearing plate between the top of the sill plate and the nut.The bolts should be undamaged and rust-free.

5. Are the crawl space perimeter walls reinforced with plywood or OSB panels?

Perimeters walls must be reinforced to prevent the house from falling over during an earthquake. This is typically done by installing plywood or OSB sheathing panels on the outside of the walls. Older homes often did not use this type of sheathing. Instead sidinboards were used, but not attached to prevent failures. The building codes recommend the installation of ½-inch plywood or OSB panels to the inside face of the walls in strategic locations to strengthen the perimeter walls.

Typical Blocking

Golden Gate Enterprises, Inc. specializes in structural and earthquake retrofit improvements and repairs. We can provide the necessary plans, engineering, and permits. Please call us today for an estimate at 510-885-0197. If you prefer, please send us an email and we will contact you.