Slide 12 of 13
Notes:
- EVALUATING EXISTING CONDITIONS
- Carefully examine the existing building and its site
- The first step in any retrofit project is to carefully examine the existing building and its site
- Determine the extent of any unique conditions that exist for that building on its site.
- Some situations will preclude the use of a prescriptive method and instead will need the services of an experienced design professional.
- The condition of the existing wood framing, particularly along the perimeter walls must be checked for fungus or insect damage and all damaged wood must be replaced.
- WHEN DO YOU NEED AN ARCHITECT AND ENGINEER?
- Important limitations
- There are several important limitations on the use of the prescriptive partial perimeter system.
- Houses that are on a sloping site, where one side or end of the building is substantially higher above grade than other portions of the building, should not use this system.
- If the ground surface along the perimeter walls has a slope that exceeds 1 foot vertical in every 10 feet of horizontal distance, special structural considerations are necessary to accomplish an effective retrofit.
- Some sloping sites may need to be evaluated by a geotechnical engineer to establish the potential risk of landsliding or other forms of ground failure.
- Houses that are over two stories in height or that exceed the maximum width and length dimensions shown on the prescriptive plan are too large to rely on prescriptive methods to provide adequate earthquake protection.
- The maximum height of new foundations are limited to 4 feet measured from the bottom of the footing
- New cripple walls are also limited to a maximum of 4 feet in height.
- If building is located on soils that are subject to liquefaction during earthquake shaking or where highly plastic clay soil exceeds 25 feet in depth, professional engineering services will be required.
- Maps indicating locations of soils subject to liquefaction are available in some cities and counties, and the local building departments will usually be aware of or have special foundation requirements in areas of highly plastic clay soils.
- For buildings located within 5 kilometers (approximately 3 miles) of a known active earthquake fault, the prescriptive method should not be used.
- Maps have been published by the International Conference of Building Officials for the entire State of California identifying these locations called “Near Source” areas.
- The 1997 Uniform Building Code requires that all buildings inside these areas be designed to resist larger forces than were used to develop the details used in the partial perimeter foundation system.
- Retrofitting buildings where these limits are exceeded requires the professional services of a licensed architect or engineer.
