Why are Blocks That Size?

The other day Daniel Nairn posted an interesting comparison of the street grids that can be found in various cities in the United States. A key question that was what made designers of cities choose one block size over another? Why for instance are the blocks in places like Tuscon, Arizona have blocks of 400 feet on a side while places like Portland, Oregon have 200 foot blocks?

To decode the block sizes of most cities one has to look at the interaction of architecture and nature, that is how local climatic conditions affect the shape of a building and it's lot.

The basic principle is that in the north the climate is primarily cold and dark, and in the south it's hot and sunny. This is more pronounced in Europe, where most of the precedents for American building types come from, and these building traditions were brought to America through the different cultures that established colonies in the New World. Thus how cities are laid out by the Spanish is significantly different from how the French, Dutch or English laid out a city, not only in tradition, but also because of where each of these cultures settled in the New World.

In southern and Mediterranean climates, there is a lot of sun and there is a lot of heat as well. So having a building close to the ground is a plus, as the earth helps regulate temperature. Also a building that is only one or two floors is good to help avoid heat rising up to higher floors. Traditional Spanish houses then are long low affairs, with small courtyards giving a little light where necessary but in general cool and dark.

Archtypical Spanish House

In the northerly climates, because of a concern for letting in light, so buildings tend to have tall windows, but also they need to deal with cold winters. So having a tall building is an advantage, as heat is retained through the stacking of floors. Keeping the lots small, narrow and nestled together helps retain heat.

So these important factors affect how the lots that such buildings need begin to make a lot of sense. A city in the northern European tradition will then have buildings being taller and narrower, having a depth of only about 35' or so for the main block and including requisite garden space, would have a relatively shallow lot size, meaning that the block size could be relatively small, at least in depth.

Ideal block in Alexandria Virginia 350' x 450'

Looking at Alexandria, Virginia as an example we see a more "southerly" northern house, having a main block of 35 feet or so with a small wing attached and a small garden behind. The lots in Alexandria are slightly deeper because of this side wing but still relatively shallow compared to the massive blocks you find in old Spanish colonial cities.

Archtypical Alexandria House

San Buenaventura, (aka Ventura), California, where I lived for two years, has lots 400 feet by 400 feet, four times the size of Portland's blocks. Ventura, was laid out according to the needs of a hot sunny climate, and like other buildings of the Spanish Colonial era obey the need for low sprawling houses. Having such low sprawling buildings, the space that this requires on the ground is a lot more and so the lots need to be significantly deeper to allow for a usable garden space behind.

Ideal block in San Buenaventura 400' x 400'

The need for a garden as a place to grow produce and even raise small livestock can't be under emphasized in a pre-industrial city. Almost all food needed to be raised locally, so having a garden was essential to city living. After the industrial revolution, with the advent of fast travel, food could be brought to market from distant lands, so the importance of a garden begins to wane. Thus we can see why Portland, founded in the latter part of the 19th century could afford to have relatively tiny blocks.

The industrial city becomes less and less subject to the necessities of the environment, and so most American cities west of the Appalachians have block sizes of more or less arbitrary sizes. Anchorage can afford to have a big block size just as much as it could have a smaller one. Really today with the advent of cars and air conditioning, the size and shape of a lot has more now to do with the needs of the car and finding parking for it than any other concern. So the key is less the depth of the lot, and more the width (being in multiples of car widths for parking.)