The Silicon Valley liquefaction zones cover much of the Bay Area and Santa Clara County, but the risks are often not well understood or investigated. We know that this is earthquake country and tremblers are to be expected. But what difference does it make where you live or work – won’t the whole valley be shaking equally?
Well, we’re Realtors, not geologists or geotechnical engineers, but we can share some resources that may help answer these questions and provide avenues for further research on this topic.
What is liquefaction?
Liquefaction refers to the ground becoming liquified, or fluid. It takes 3 ingredients to liquefy land: loose sediment, water, and strong shaking. This loose, saturated soils when shaken to a certain point no longer behave like a solid and can slide, open, and swallow anything above it.
In 2010 and 2011, New Zealand experienced this and it made worldwide news. The Science Learning Hub website states that “During the Canterbury earthquakes of September 2010 and February 2011, liquefaction caused silt and fine sand to boil up and bury streets and gardens and caused buildings and vehicles to sink.”
But I never heard about that happening during the 1906 San Francisco quake, or the 1989 Loma Prieta quake in Santa Clara County – that means it’s not a risk here, right? Wrong. The USGS Liquefaction and Sea Level Rise explains that a relatively dry rainy season in 1906 lowered the liquefaction risk, and the 1989 quake happened near the end of the dry season when groundwater levels were at their low point.
Silty, sandy soil will respond very differently to bedrock and clay in the case of extreme shaking. So no, the valley won’t all be shaking equally in the case of a large tremor. Liquefaction hazard zones will likely get the worst of it. That’s why this designation matters so much.
What is a liquefaction zone?
After the Loma Prieta earthquake in 1989, the Department of Conservation, California Geological Survey created maps to make residents aware of areas in which there are increased risks from earthquake shaking due to landslides or liquefaction and to make sure that construction in those zones have extra investigational requirements to build safely. The liquefaction zones are noted by the state to be more susceptible to dangerous liquefaction in the event of an earthquake. You can learn more about these and related issues at the California Department of Conservation’s website. (more…)
I recently published a piece on post-tension slabs, which is more used in new construction, however it’s not the most common type across existing homes in the South Bay. While basements are not often found in the South Bay, crawlspaces are. You’re most likely to encounter raised foundation, known as perimeter or raised perimeter, also called post and pier, foundations.
Still images from historic reels shared by History San Jose showing one of the city’s suburban developments of the 1960s and the installation of this type of foundation. Click to go to the original video on Youtube. Edit: Unfortunately the video appears to have been removed. I’m leaving the link in case it is re-uploaded.
An Introduction to Raised Perimiter Foundations
What is a Raised Foundation, or a Perimeter Foundation?
A raised foundation, perimeter foundation, or raised perimeter foundation is one that supports a structure while lifting it a few feet above the ground level, as the name implies. It is called a perimeter foundation because the exterior walls are held up by a reinforced concrete stem wall, while the body of the house is supported by a post and pier construct. (In earthquake-free parts of the world, the stem wall may be brick or cinder block.) These are all names for the same thing.
This type of foundation is usually only raised around 1-1/2’ – 2’ high, one or two stair steps above ground level. Much taller would make a top-heaviness that becomes less stable against seismic force.
Alternatively, some floors might be set quite low. Two rooms in my single-story house are a step below the rest. They are still raised on posts and piers, but they are distinctly lower than the rest. This is called a sleeper floor. In the crawlspace, this translates to very tight quarters, and I have met professionals who will, and who will not, be able to work in that space.
What about perimeter and slab both in the same house?
If a home is described as having both a perimeter and a slab foundation, most of that time it means that the majority of the house has a raised foundation, but the family room or other room directly behind the garage is on slab. This is very common in Silicon Valley
What is a Post and Pier Foundation?
Post and pier (or girder) foundation blueprint, including crawlspace access point and lowered subfloor and sleeper floor.
Post and pier, or beam and post foundation, supports a structure by raising it on individual posts distributed evenly beneath a structure. Each pillar of support consists of three parts: the pier, the post, and the beam.
The pier is a vertical anchor set deep in the ground, usually made of concrete (but occasionally other resistant material like steel). The pier rises a few inches above ground level and is attached to a vertical post. The post, or column, is generally foundation-grade treated wood. This post attaches to a horizontal beam, or girder, which directly supports the floor joists. Occasionally, the pier may act as a post and connects directly to the beam, but that is very uncommon in my experience.
These type of foundations can be built without the perimeter wall, but functionally it is very different. You will often see decks built this way, including decks that are attached to homes with a raised perimeter foundation. Without the continuous stem wall the cost to construct is significantly less, but the resulting structure is more vulnerable to the forces of nature, to lateral seismic force, and to pests and wildlife. It also has greater airflow beneath, which is good in places with regular flooding, but provides less insulation from below.
Some Silicon Valley homeowners spruce up their yards and gardens in spring and summer with tanbark or mulch. While this is a very common practice, and often encouraged as a drought-friendly gardening option, it can be a bad idea if it is too close to the structure, especially the home’s foundation.
Tanbark is simply small bits of wood, and most common mulch is often no more than shredded wood. Why is that bad? Wood is food for termites and piles of tanbark or mulch can invite and hide them as well!
Tanbark or Mulch?
Mulch is the more widely used term and it can cover a broad scope of materials, but the most common type you will find in stores (and in Bay Area gardens) is the woodchip mulch. If you ask for mulch at a hardware store, this is most likely what they will show you. In the local vernacular, we often refer to mulch as the fine, thin, or decomposed stuff – we have a different name for the larger bark and wood chips.
I learned only recently that tanbark is something of a local term that people from other parts of the state or country may not be familiar with. Here in the Bay Area we call the stuff you commonly see underfoot at playgrounds or piled thick on the planted berms around a shopping mall parking lot by the name of tanbark. Some people may reserve the name for the large chunky bark chips while others will call just about any wood chip substrate by that name. So tanbark is, in fact, a mulch.
Homeowners and sellers wanting their home to make a good first impression are often tempted to apply mulch or tanbark in otherwise bare patches around their yard, but you can wind up with far bigger (and more costly) problems if it’s too close to the foundation!
Edit: this post was originally published July 17, 2010, but the concerns are still as real as ever. Broken links have been updated, but the body of this article is, for the most part, left as it originally was over a decade ago.
Since early July, fire danger signs have been out at Belgatos Park in Los Gatos (and I suspect at other parks throughout Santa Clara County too). To the right is the sign at the park’s main entrance. It admonishes the visitors:
“High Fire Danger No Smoking No BBQs”
To anyone who’s lived in Silicon Valley long, this is understood – the fire danger is quite high here in summer. Unlike most of the east coast, it does not rain here in summer (at least not often and not much), and our green grasses and plants of spring turn to kindling very quickly. One stray match, hot cigarette butt or one illegal firework can smolder into a flame which grows fast with the smallest amount of wind to destroy property, animal life and potentially human life, make breathing bad for days and leave a scar on the land.
This sign at the entrance may not feel very compelling to some as the lush green grass in the background would seem to contraindicate restraint. But venture to the park’s side entrance on Bacigalupi Drive (or hike up the trails) and you’ll understand immediately why this is nothing to take lightly.
Except for one little tuft of partially green grass, “cardboard hill” is entirely dry. So is the rest of this beautiful open space.
If you live close to or have open space in San Jose’s Alum Rock, Almaden, or other east foothill areas or the west valley places like Los Gatos, Monte Sereno, Sartoga, Cupertino or anywhere the foothills, your property is likely considered to be in a high risk fire hazard zone. If so, each year you are mailed information from Cal Fire reminding you of your obligation to provide clearance around your home and to cut down the dead brush.
Just outside of the main entrance to the park there’s a large and open lot which has a few trees, some prickly pear, and a lot of grasses and weeds in winter and spring. (It also had a rattlesnake it in by the prickly pear when my daughter walked past with our dog one day a month or two ago.) Below is a pan of two pics I took with my Blackberry and later stitched together – the park entrance is out of sight but is a little to the left of this photo.
These owners have done as needed and disked the field to help prevent fires or the spread of fires.
There are things you can do to “harden” your own home and create defensible space if you live near open space to make it more resistant to fire. Check out the whole list on the Cal Fire site, “Prepare for Wildfire“.
Gas cooking is highly in demand, sought after for the quick response time and precision with heating and cooling. The vast majority of our clients have a strong preference for gas cooking over either induction or regular electric cooking.
In recent years, studies have shown that gas stoves can be a significant source of indoor air pollution. When in use, the hood should always be in use to foster healthy ventilation. That part alone is often forgotten, but it turns out that gas ovens and cooktops may be polluting even when no one is cooking.
Health hazards of gas cooking
Last week, the New York Times published the findings of a Stanford Doerr School of Sustainability and PSE Healthy Energy, a non-profit), study which found that in the 87 homes with gas stoves tested in Colorado and California, benzene was detected in every home, both in the kitchen and beyond, after just 45 minutes of using either the oven at 350 degrees or a single stove burner.
Benzene is a cancer causing agent and no safe levels of exposure to it are known. It is worth saying again: benzene was produced by gas cooking in every tested case.
In about a third of the tested homes, the benzene level exceeded what would be found with second hand smoke. The study also suggests that the smaller the home, the worse the results.
In many cases, that means the dark home needs to be transformed into a light one.
How to make a dark home a little more light: start with the windows
How can a home owner make a house or home be – or seem – more bright? One of the biggest “offenders” in this area involves windows! Here are a few window-related problems that can make a home feel significantly darker than necessary, together with some potential solutions:
Tinted windows, such as yellow or other colored glass at the front door or entry way: replace with clear or translucent, colorless glass. If there’s a darkening film (for instance, for privacy), remove it and replace with a clear or translucent but uncolored film instead.
Curtains/blinds which obstruct part of the window: get tie backs to pull them further back and let more light in (goal is to not obscure windows at all). Easiest of all are those which use magnetic clasps and do not require any hardware be attached to the wall.
Furniture blocking windows should be moved or swapped out for lower items that do not cover up any of the windows. I see tall headboards often situated right in front of the glass panes – they are counter productive. Perhaps remove the headboard, or place the bed in another location?
Shrubs and trees covering some of the window: trim back so the window’s glass panes are 100% visible, if at all possible, to let maximum light in.
And of course, do make sure your windows and tracks are sparkling clean!
Many times, homeowners look at the size of their home and assume that all living space is equally valuable on a price per square footage basis. That’s not always the case.
Expansions: Distinguishing Square Footage
In Silicon Valley, we frequently see tract neighborhoods of smaller houses, say 1,000 to 1,500 SF, in which additions have been made. Sometimes it’s an unattractive “pop-up” or “box on the top” which doesn’t match the home’s design or the look of the neighborhood. Other times it’s a tasteful expansion which blends seamlessly into the home. So how differently will these be priced?
Lawn mushrooms are the bane of gardeners everywhere; we usually refer to these unwanted pests as toadstools. Toadstools are really the same thing as mushrooms but are often poisonous.
These members of the fungus family pop up when we get a little moisture, so they are a common sight once rain appears, as it has been doing a lot lately. They are not harmful to the lawn if left alone, but people with pets and children may be concerned about these unwanted visitors being ingested, causing sickness or death – so for that reason, it may be advisable to rid your yard of them.
Tips for removing lawn mushrooms
These fungi thrive on decomposing plant matter, whether it’s old roots, sawdust, animal droppings, or a fallen log. They also thrive in dark, wet areas. Some of the suggested treatments involve these steps:
Remove what they are feeding on, such as pet waste, a buildup of mulch or leaves, etc.
Wearing gloves, carefully cut or remove the lawn mushrooms and put them into a plastic bag that you seal so that it cannot reproduce.
Aerate or de-thatch your lawn.
Add soapy water to the area where you have removed the lawn mushroom.
Another option, perhaps not the best first choice, is to apply a fungicide.
Do wear gloves when handling them directly. Want more info? Here are a few articles to help:
High Voltage Power Lines from around the West Valley.
High voltage power lines are a “location issue” that impacts real estate values, and it sometimes elicits worry regarding safety.
High voltage power lines: how far is far enough?
Something we have spoken about recently with our clients is being far enough away so that if the tower and high voltage power lines were to fall, they’d miss your home and property. In our recent series of atmospheric rivers in January 2023, in San Jose one of these large transmission towers did fall down. It’s rare, but not impossible.
I have not seen a website that can tell us how tall any given tower is, but from what I have read online, it seems that most of them are under 200 feet tall, but some could be higher than that. In most cases, that puts the lines about 4 houses away if the lots are a typical 6,000 SF lot of 60′ across the front and 100′ deep.
We cannot speak to the concerns around potential increased risk of cancer or other problems. Each consumer should research that issue on his or her own.
Where are the high voltage power lines?
Years ago, I painstakingly mapped out the transmission lines from what I knew on the ground and what I could tell from tracing the Google satellite view. (You can find that link near the bottom of this article.)
Today, though, there’s something better than my map available online. The California Energy Commission has a map of the transmission lines that you can view usingTHIS LINK. Or click on the image at the left.
From the landing page you can zoom in or out. It covers the entire state of California – you might find it interesting to navigate around a little.
Also, a few years ago, PG&E published an interactive map where you can view the location of electric lines (I’ve filtered the imbedded map below to show Electric Transmission Lines in the South Bay), and another map of natural gas pipelines, searchable by address. This doesn’t cover the entire state, but it does cover all of the Bay Area / Silicon Valley.
The PG&E map:
On the map I hand-drew at the bottom of this article I did also include the location of schools. Quite a lot of schools do have transmission lines present.
What other location issues are there to factor in? (more…)
Pet rats – the kind you buy at the pet store – can make the most adorable friends. Our daughter had one as a pet and she was a very beloved family member.
But rats in the roof, attic, crawl space, walls and landscaping are not so adorable. They wreck havoc and can cause damage to home and health. Wild rats gnaw on wood and wires, and they carry fleas that can spread disease. Further, their droppings can be unhealthful, too. There are many reasons to make sure that rats aren’t at home in your home, garage, or yard.
What kind of rats exist here?
In Silicon Valley, the predominant type of wild rat is the Roof rat (also known as the Black Rat, Shop Rat, or Tree Rat). They are identifiable because their tail is longer than the head and body together. They are dark brown or black in color. They do not live only on roofs or in attics, but do appear to prefer higher places, like branches in trees.
A lesser seen rat in the San Jose area is the Norway rat (also called the Wharf Rat, the Sewer Rat, or the Brown Rat). This rat has a shorter tai; and larger, heftier body with light brown or gray coloring, and may be seen in more rural or less developed areas.
A few years ago, a neighbor of ours found a dead rat in his yard, and he called The Santa Clara County Vector Control District office to come out and help him identify if there was a problem with rats getting into his home or not, and to shed light on the issue of why this critter recently appeared in his home. The officer came out and performed this service for free, enlightening my neighbor as to access points and providing a helpful brochure about rats and what attracts them.
Landscaping and rat harborage
I’d heard that Italian Cypress trees, juniper and ivy were all bad – that is, that they attracted rats and create a nice setting for them, or rat harborage. What I did not realize is how many other things do too. (more…)
Christie's International Real Estate Sereno, Los Gatos, CA 95030 408 204-7673 Mary@PopeHandy.com License# 01153805
Clair Handy, Realtor
Christie's International Real Estate Sereno 214 Los Gatos-Saratoga Rd Los Gatos, CA 95030 ClairHandy@sereno.com License# 02153633
Mary & Clair sell homes throughout Silicon Valley: Santa Clara County, San Mateo County, and Santa Cruz County. with a special focus on: San Jose, Los Gatos, Saratoga, Campbell, Almaden Valley, Cambrian Park.
Mary Pope-Handy, Realtor
ABR, AHWD, CIPS, CRS, SRES
Christie's International Real Estate Sereno
DRE License #01153805
“Helping nice folks to buy and sell homes in Silicon Valley since 1993”
Clair Handy, Realtor, GREEN
Christie's International Real Estate Sereno
DRE License #02153633
email@example.com “Helping nice folks to buy and sell homes in Silicon Valley”
This is the Valley of Heart's Delight blog , covering Silicon Valley real estate - Santa Clara County, San Jose, Los Gatos, Cupertino, and nearby communities in the South Bay Area and lower Peninsula. Find info on neighborhoods, disclosure issues, buyer and seller tips, and housing market conditions in the west valley and most of the county.Please also see my other websites and real estate market statistics site, which are listed in the sidebar, above.
Mary Pope-Handy, Realtor
ABR, CIPS, CRS, SRES
DRE License #01153805
“Helping nice folks to buy and sell homes in Silicon Valley since 1993”
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