California is earthquake country. From the iconic 1906 earthquake, to the daily reminders that we live on top of 3 major tectonic faults, earthquakes are a big part of the local consciousness. You would imagine that, after San Francisco was almost leveled in 1906, the building codes would change to take into account such large tremors and build stronger houses. Unfortunately, that's not the case. It's true that a majority of buildings in San Francisco are wood-frame houses with at most 3 floors, which tend to be pretty flexible and withstand earthquakes reasonably well (although they can easily succumb to fire). Still, lots of older houses are vulnerable: they can shift and fall off the foundation, or the lowe stories can crumble under the weight above them. This is especially true of soft-story homes, which are prevalent in the Sunset and Richmond districts.
To reduce earthquake risk, it is possible to retrofit an older home to better resist a large earthquake. There is a lot of good evidence that such retrofitting can make a big difference.
So what goes into a retrofit?
Foundation work. Many older houses literally "sit" on the foundation with no additional reinforcement. When the ground shakes, it can "push" the house off the foundation. Even a small push, say a few inches, can have disastrous consequences, it can sever water, sewer, and gas pipes, start a fire or worse. To mitigate this, the house can be bolted to the foundation, so that the ground and the house move as one.
Cripple wall work. Most houses don't sit directly on the foundation, to prevent the wood from getting damaged or weakened by natural ground moisture and the like. Houses are either built on top of a narrow "crawl space", or, in the case of soft-story houses, the living quarters are built above the garage. In an earthquake, the heavy part of the house above carries a lot of inertia, and if the underside is bolted to the ground, the house above can shatter the walls underneath and fall. To mitigate this, the lower walls can be reinforced with plywood shear walls that strengthen them and essentially stiffen the house, preventing the upstairs from swinging wildly in a quake.
Garage opening reinforcement. Even with bolts and shear walls, the garage door opening remains a major weak point, as it weakens one of the key structural walls of the house. This can be reinforced with a steel frame or a steel beam to give it the same strength as the other 3 walls.
Here's what it looks like (courtesy of seismicsafety.com):
For most houses, the retrofit work can be done just with the help of a skilled contractor, who's qualified to install bolts and shear walls. For some houses, notably those on a steep hill, or soft-story designs, the help of an engineer is needed to design the retrofit and compute the appropriate material strengths, after which the contractor can install it.
ABAG has a wealth of information to help people decide the risk of an earthquake and the impact in their specific area. In particular, the maps of shake intensity and liquefaction risk are extremely useful. In San Francisco, having your house on top of a hill can dramatically reduce both shaking and liquefaction, though it does increase the changes of a landslide. Sadly, the Marina with its gorgeous houses and amazing views, is built on top of landfill from the 1906 earthquake, so it's very vulnerable to an earthquake; it's no accident that in the relatively minor 1989 Loma Prieta earthquake, the Marina suffered the most damage (map courtesy of thefrontsteps.com).
Another way to mitigate against earthquake risk is to get earthquake insurance. In California, this is of questionable utility: if a major earthquake were to hit, the CEA would probably run out of money, at which point people say that FEMA would have to step in and help the reconstruction. During that time, people would probably have to live in temporary houses, like the ready-made earthquake shacks of yesteryear. Still, having some earthquake insurance can provide a good cushion in the case of a major natural disaster.
I personally found that learning about earthquakes made me worry about them less and take the necessary steps to increase our safety. I realize there are no guarantees, but doing even little things can go a long way towards helping deal with this reality. And I certainly wouldn't trade living in San Francisco for anywhere else, earthquakes and all.
Renewable energy is becoming increasingly more visible in our society. The recent oil and food price spikes, the impending opening of the Northwest Passage, the coral bleaching in the ocean all point to the fact that we consume fossil fuels at unsustainable rates, and are changing our environment for the worse. Changing to renewable energy makes both economic and moral sense.
Of the many ways to produce renewable energy, solar is a big focus these days. In the US, the federal government has a generous subsidy, which looks to be extended in the following years. In California, there is an important state subsidy, and a generous San Francisco subsidy. (Lest you wonder, even foggy San Francisco gets plenty of sun.)
In California, grid electricity is produced by PG&E, mostly using natural gas. The solar incentives aim to encourage private individuals and businesses to install solar panels and feed electricity back into the grid, thereby offsetting some of their consumption. If the solar installation produces more than the individual consumes, their PG&E bill can be negative (they get a check each month). In most cases, the solar panels would offset some fraction of the consumption, typically the expensive kWh's, more on this below. Here's what this looks like (video credit Solar City):
One natural question at this point is: why feed the electricity back into the grid, instead of running your house directly on it? For one, the solar panels only work during the day. To have electricity at night, you would need to install a fairly large set of batteries to store excess energy. Batteries are very costly and often an environmental nightmare (containing acid or rare metals that are expensive to synthesize or extract). Second, solar panels energy output varies considerably between seasons (in the northern hemisphere, the sun's efficiency is very different in the winter vs. the summer), or even between days (on a cold, stormy day with cloudy skies, the output is quite different than on a warm, sunny day). Third, most electrical appliances expect a steady electrical output (110v, with small error margins), which are difficult to maintain even from a good battery bank. The goal of solar is not to necessarily replace the grid entirely, but rather to offset enough to substantially reduce our pollution and dependence on fossil fuels.
Solar cells convert sunlight into electrical current. The conversion is pretty inefficient, around 20% of sunlight gets transformed to electricity. However, given that direct sunlight on average produces 120 W/square meter, on an 8 hour sunny summer day we can recover almost 200 kWh of electricity using a modest 1 square meter solar cell array.
Solar panels produce DC current, but the grid operates on AC, so the output from solar panels has to be converted to AC using an inverter. This exacts another small efficiency penalty (around 20%), and has to be tuned to the size of the solar array.
Solar panels are expensive (largely because they're not yet mass produced, so they can't leverage economies of scale). Absent generous subsidies, in order for them to make financial sense, they have to be sized as a function of household consumption. As of the time of this posting, PG&E uses a tiered price structure for electricity: the first 256 kWh are the cheapest, at 11c. If you consume more than 256 kWh, the price increases quickly, up to more than triple:
11c/kWh - 0 -100% baseline (256 kWh)
13c/kWh - 100-130% baseline
22c/kWh - 130-200% baseline
31c/kWh - 200-300% baseline
35c/kWh - over 300% baseline
For a residence, it makes sense to look at a year's worth of electricity bills and figure out what is the consumption pattern. In a warm area like California, odds are you'll use lots of electricity in the summer (A/C) and less in the winter when it's cooler, but not cold enough to require heating. One solar strategy is to get a solar array big enough to offset only the expensive kWh in the summer (those at 30c or more). There is no magic formula here, each house is different, although in very broad terms a 2.5-3.5 kW solar array should do the trick for a lot of average-size homes.
Before embarking on a solar project, it makes sense to first optimize your consumption using the cheapest tools: replace all incandescent bulbs with CFLs, configure computers and TVs to go into standby when not used, increase the temperature of the fridge and freezer, insulate the attic to keep cold air in, and so on. This can have a dramatic effect on your electrical consumption, as much as 30% reduction! At this point, take stock of your usage and size the solar array as a function of the new energy consumption numbers.
Go solar!
For most houses, the retrofit work can be done just with the help of a skilled contractor, who's qualified to install bolts and shear walls. For some houses, notably those on a steep hill, or soft-story designs, the help of an engineer is needed to design the retrofit and compute the appropriate material strengths, after which the contractor can install it.
ABAG has a wealth of information to help people decide the risk of an earthquake and the impact in their specific area. In particular, the maps of shake intensity and liquefaction risk are extremely useful. In San Francisco, having your house on top of a hill can dramatically reduce both shaking and liquefaction, though it does increase the changes of a landslide. Sadly, the Marina with its gorgeous houses and amazing views, is built on top of landfill from the 1906 earthquake, so it's very vulnerable to an earthquake; it's no accident that in the relatively minor 1989 Loma Prieta earthquake, the Marina suffered the most damage (map courtesy of thefrontsteps.com).
Another way to mitigate against earthquake risk is to get earthquake insurance. In California, this is of questionable utility: if a major earthquake were to hit, the CEA would probably run out of money, at which point people say that FEMA would have to step in and help the reconstruction. During that time, people would probably have to live in temporary houses, like the ready-made earthquake shacks of yesteryear. Still, having some earthquake insurance can provide a good cushion in the case of a major natural disaster.
I personally found that learning about earthquakes made me worry about them less and take the necessary steps to increase our safety. I realize there are no guarantees, but doing even little things can go a long way towards helping deal with this reality. And I certainly wouldn't trade living in San Francisco for anywhere else, earthquakes and all.
