BUYING A NEW HOME – PART 2: The Site

by David.

In this part 2 on Buying a New Home, I’m going to speak to some of the important considerations of the site that you’ll want to know about before buying your new home.

TYPE OF SOIL

The type of soil found on the site of the home is important to the stability of the building for numerous reasons. Some soils, like clays, are more susceptible to sliding, especially when rain lubricates the different layers of the clay. Soft soils, like those located near the bay, can become saturated during an earthquake turning the soil into quicksand and damaging a building.

The type of soil also affects the intensity of an earthquake shaking in a seismic event. Softer soils, like those found alongside the bay and in landfills, will amplify ground shaking and cause more damage. Structures built on bedrock that are near a fault have shown to perform better in earthquakes than those built on looser soils much further from the epicenter.

SLOPE STABILITY

The considerations for buying a home on a slope are usually greater than those that are not. It’s imperative to know if you’re in an area of an active landslide or creep zone by either looking at landslide maps from the city or consulting a soils engineer. Poor grading during construction can also create a localized landslide that is more difficult to detect and wouldn’t be on a landslide map. As mentioned above, earthquakes can also cause hillside soils to move that would otherwise be stable and thereby increase the potential for a landslide.

It’s a good idea to contact a soils engineer if you are purchasing a property on a slope or a hillside, or atleast contact an engineer to assess whether a soils professional would be necessary. Local soils engineers will often know where active slides and faults are located and can provide essential information on how these hazards may affect your home. For some resources of your own, see the bottom of this article.

DISTANCE TO FAULTS

The greatest building damage is dependent on the amount of ground shaking. The amount of ground shaking is dependent on the distance to the fault and as mentioned before, the type of soil underneath the building.

The greatest risk to a building near a fault is a ground-surface rupture beneath it. This is a major risk for homes that straddle a fault and one that no building can withstand. It is thereby very important to know how far any new home is from any active faults. For ones that are close, it’d be prudent to get it checked out by a soils engineer or geologist with adequate maps to local any traces of the fault.

I hope this gives you a basic idea of what to look for on the site of your potential new home. If not, please contact me for for a more in depth look at your home.

BERKELEY HILLS LANDSLIDE MAP

http://www.akropp.com/resources/downloads

BAY AREA SOIL TYPES AND SHAKING HAZARD MAP

http://earthquake.usgs.gov/regional/nca/soiltype/

MAP OF THE ACTIVE TRACES OF THE HAYWARD FAULT

http://earthquake.usgs.gov/regional/nca/haywardfault/