Home Not Bolted (or Not Properly Bolted) to Foundation

Larger imageThis home wasn’t bolted and slid off its foundation. Sometimes the damage can be so bad that houses have to be demolished.

Source: Office of Emergency Services

The Problem

Houses that are not bolted to the foundation can move off their foundations during earthquakes.

How to Identify

  • Go down into the crawl space – the area between the first floor and the foundation – to find out if your house is bolted to its foundation.
  • Look for the heads of anchor bolts that fasten the sill plate – the wooden board that sits directly on top of the foundation – securely to the foundation. (See Drawings A & B below)
  • You should be able to see the large nuts, washers, and anchor bolts, installed at least every 4 to 6 feet along the sill plate. Steel plates are sometimes used instead of anchor bolts. (See Drawing B below)


Remember

  • It is very expensive to lift a house, and place it back on its foundation.
  • Homes moving off their foundations can cause gas lines to rupture, which in turn can result in fires.

Larger imageA - Installation of Foundation Anchor Bolts (Note: Washers are now recommended to be 2" square washers)

Source: California Seismic Safety Commission

Note
If your home has no foundation, or an old concrete foundation, see Other Foundation Issues.

The Solution

  • Drill holes through the sill plate into the foundation and install anchor bolts.
  • If there is not enough room to drill, you can attach steel plates to hold the sill plate to the foundation.
  • Larger imageB - Anchor bolts or steel plates. A home's crawl space may be formed by a cripple wall (see Weak Cripple Walls page) between the foundation and the floor joists or the floor joists may rest directly on the sill plate. In either case, you should be able to see the heads of anchor bolts or steel plates installed at appropriate intervals. These fixtures fasten the sill plate to the foundation.

    Source: California Seismic Safety Commission

  • Anchor bolts have to be installed properly for them to be effective.
  • You must obtain the proper permits from your local Building Department before beginning work.


How-to Resources


NOTE: Slab Foundations

Some homes are built directly on concrete slabs. These houses do not have crawl spaces and cripple walls.

Nearly all homes with slab foundations that were originally built to code will have anchor bolts or straps. However, if the house is not bolted to the slab, you have an earthquake weakness.

Newer homes generally have anchor bolts or straps. If you have an unfinished garage, you may be able to see the anchor bolts.

You are not required to remove siding, drywall or plaster to determine if your house has anchor bolts.

©2016 SCEC Southern California Earthquake Center @ USC