The Grizzly Peak Mitigation Area (GPMA) includes every home in Berkeley east of Grizzly Peak Blvd, as well as parcels “addressed on the west side of Grizzly Peak Blvd.” At this time, it is the only part of the WUI that is subject to strict Zone 0 regulations under the “EMBER” legislation.
What do we know about the GPMA? To figure it out better, we entered every address included in this description in a spreadsheet, and did some research on the properties included.
The research process
The data gathering phase was intense! We entered every Google Maps address into the spreadsheet, then we looked up every property in real estate databases to validate that the properties were real, and enter the lot size. The we inspected every vacant lot in the Berkeley GIS database, inspected the satellite pictures to verify if they existed or not, and entered fictitious addresses with calculated lot sizes. We also went on several tours doing visual inspections—in particular, we changed the vacant status for each property that is currently being build (although we don’t always know what the street address will be).
We validated every one of these properties—so we cannot have too many in our list, unless some of the properties we believe are vacant area actually parts of double lots where real estate databases do not take the second lot into account. It is possible, however, that we are missing some—in case some properties are missing from the Google Maps database (that happens) or if we accidentally did not enter them—if that is the case, we expect to be missing no more than a handful.
Overall results
We found a total of 993 properties in the Grizzly Peak Mitigation Area. Of these 993, only 960 actually have a house on the lot, either built or in active construction.
Not surprisingly, the bulk of the vacant lots are on the periphery of the area (close to Tilden Park), in particular, but not only, in the south end of the GPMA. Streets with several vacant lots include Wildcat Canyon, Hillview, Park Hills, Hill Rd, Summit Rd, Grizzly Peak Blvd and Woodmont.
What we learned about the GPMA’s properties
We were surprised at the size distribution of the lots.
The Hillside as a whole, according to real estate websites, has an average lot size of 4,500 ft2. We entered the size of every lot in the GPMA. The average lot size in the GPMA, we found, is a bit over 8,150 ft2, although, if you remove the vacant lots, often large and with irregular shapes, it goes down to a bit over 8,050 ft2. This is much larger than we expected! The median lot size was of course much smaller, around 6,550 ft2, meaning that the average number was skewed by a small number of very large lots.
The house size we found was also a surprise, but in the opposite direction. The median for the Hillside as a whole is about 2,300 ft2 (calculated as a median price of $1.7M divided by an average price/ft2 of $745). We did not enter the size of every house in the GPMA in our spreadsheet, but we did a statistical analysis, by picking a smaller neighborhood of 101 homes with a fairly representative lot size (the median lot size was 5,970 ft2, vs a median lot size for the whole GPMA around 6,550). We found an average house size of 1,970 ft2, and a median size of 1,870 ft2. Because the average and the median are almost equal, this implies a much more uniform distribution of houses, where there is not a big asymmetrical skew among house sizes. It was quite a surprise to us to find that the average house size in the GPMA is quite a bit smaller than on the Hillside. In fact, Berkeley as a whole sees an average house size of 2,885 ft2, so the houses in the GPMA are much smaller.
Interestingly, while the lots are much bigger than the average lot size on the Hillside, the houses are quite a bit smaller. This implies that the GPMA has, overall, a lower “luxury” standard than the Hillside as a whole: larger but probably cheaper lots (otherwise the houses would be larger than the average Hillside house), and smaller homes. It also makes sense when we consider that the lower, more luxurious streets near the university and around Santa Barbara were mostly built in the early part of the 20th century, while the Ridge was mostly build after the Second World War.
This matches well with the Ridge Firewise groups’ understanding of their members: there is a general belief that more than half of their members are on fixed income.
Background: statistical analysis of sample size
The calculations we did one home sizes were based on a sample size of 101 houses. The houses were chosen as all-contiguous houses in five immediately contiguous blocks of 3 streets, so that there could not be any choice bias by the sampler him/herself. The five contiguous blocks were chosen to get a close approximation of the lot size between the actual sample and the GPMA.
How accurate was the estimation based on the sample size?
The standard deviation for our sample of 101 houses was 782 ft2. Using a standard statistical equation for the margin of error, using a Z-score of 1.96 for a 95% confidence level, we get:
Margin of error = 1.96 x standard deviation/ SQRT(sample size) = 1.96 x 782/ SQRT(101) = 152 ft2.
Therefore, we have a 95% confidence level that the average house size in the GPMA is within 152 ft2 of 1,970 ft2. It is reasonable to expect similar accuracy for the median (although the math is different).
Conclusions
Many surprises all around with these unexpected results: a total number of houses around 960 (possibly a bit more if we missed a few), larger but obviously cheaper lots than the average lots in the Berkeley Hills (if real estate statistics are valid), and much smaller houses than both Berkeley as a whole and the Berkeley Hills.
Study author: Michel G. Thouati. This study was undertaken by HelpBerkely.org in collaboration with BerkeleyFirewise.org.