Standard Plan Set for Residential Seismic Retrofitting

Left to right: cripple wall before retrofit, mudsill anchor bolt and blocking, shear plywood vents, plywood bracing, floor framing clips

Standard plan set

Cities and counties in the San Francisco Bay Area have worked together to develop this Plan Set to improve the likelihood that homes will be habitable following future earthquakes.

Note: You do not need to hire an engineer to complete this plan set!
Standard Plan Set A – 24” x 36″ – but legible on 11″ x 17″
Model Resolution for adoption by cities and counties

These sheets are difficult to view on a computer screen, but are suitable for providing to your city or county building department to obtain a building permit.

NOTE – ABAG’s Executive Board adopted the 2008 version of this plan set on Sept. 18, 2008. Therefore, the files on this page have been updated.

What is the plan set?

This plan set is a 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 an engineer to develop 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.

Who can use this plan set?

If your home meets all of the following criteria, your house qualifies to use this plan set. If your home does not meet one of these criteria, you should contact an engineer.

  • One or two family residential structure
  • Two stories or less
  • Wood-framed construction
  • Has a continuous perimeter foundation (ignoring the immediate areas surrounding the fireplace and porches)
  • All of the cripple walls are less than four feet in height (see top left picture for an example of a cripple wall)
  • If home has brick or stone veneer along the exterior walls (excluding the chimney), it is less than four feet in height above the foundation
  • Roofing is a material other than clay tile

What does the plan set say needs to be done to my house?

The three main components of this plan set are demonstrated in the pictures at the top of this page. They include:

  • Bolting the cripple wall mudsill to the foundation
  • Installing plywood brace panels to the cripple walls
  • Connecting the cripple wall to the floor above

Why Is the plan set needed?

ABAG concluded that most homeowners are not retrofitting – and those that retrofit are not doing all the work needed to significantly change the likelihood that their homes will be habitable following future earthquakes. One of the problems that homeowners mentioned in an ABAG survey was that they did not know what to do. This plan set is a tool to help homeowners know what needs to be done. They can use the plan set to get bids from contractors, or, if experienced, can do the work themselves.

Why 24″ x 36″ and how do I print these large sheets? And how many of these sheets do I need to submit to my building department?

The plan set is two sheets, each of which is 24″ x 36.” This size is standard for plans required by city and county building departments for permits. You can view the plan set on your computer. However, most people don’t have the capability of printing these large sheets. You can email them to your local copy shop or download them to a CD and take them to your local copy shop to make copies. However, they are legible when printed on 11″ x 17″ paper.

In addition, we are working with city and county building departments to make the plans available at their counters. Alameda, Berkeley, El Cerrito, Hayward, Livermore, Newark, Oakland, and San Leandro have these plan sets available at the counters of their building departments.

The plan set states that the applicant for a permit should submit two copies of the plan set to the building department. Some cities and counties may have different requirements. Be sure and check with your local building department to confirm that this is the correct number of plan sets required.

Who developed the plan set?

The plan set was developed by a committee representing the East Bay, Peninsula, and Monterey Bay chapters of the International Code Council (ICC), along with representatives from the Association of Bay Area Governments (ABAG) Earthquake Program, the Structural Engineers Association of Northern California (SEAONC) Existing Buildings, Seismology and Structural Standards Committees, the California Building Officials (CALBO) Seismic Safety and Emergency Preparedness Committees, the Earthquake Engineering Research Institute (EERI) Northern California Chapter, and building contractors specializing in home retrofit.

Why does the plan set allow use of either 1/2 inch or 5/8 inch bolts, while the 2008 code only discusses the use of 5/8 inch bolts?

The plans intentionally allow the use of EITHER 1/2″ or 5/8″ bolts. The calculations in the plan set table were run for both types of bolts. Because the 1/2″ bolts are smaller in diameter, more of these bolts are required than if 5/8″ bolts are used. Both should be acceptable for use for an engineered design, which this is. While 5/8″ bolts are a default value for conventional new construction, the use of 1/2″ bolts in actually preferred by many as the demand on an existing foundation and mudsill at the specific point where the bolt enters the mudsill and foundation is actually a bit less.

Is it a mistake, or does the plan set require use of 3 x 3 x 0.25 inch washers, while the 2008 code requires use of 3 x 3 x 0.229 inch washers?

Either thickness of washers is acceptable. The key is that they should be 3″ by 3″ rectangular washers, not the thin round ones usually present in existing older homes.

The plan set allows the use of expansion anchors, but most people don’t have copies of the ICC ES report for detailed information on how many might be required. Is this an issue?

Those developing the plan set had access to the ICC ES report on expansion anchors. The calculations for how many anchors are required has, therefore, already been performed.

Has ABAG itself acted in support of the plan set?

Yes, ABAG’s Executive Board passed a resolution at its December 2004 meeting in support of the original version of this plan set. A second resolution, adopted at its September 2008 meeting in support of the 2008 version of the revised plan set, was passed in support of the revised verson of this plan set.

Last updated: 10.12.2013