Saturday, June 11, 2011

Garages and Backyards

Expanding on a comment I made on this Old Urbanist post, I have provided a site design for four blocks offering a reasonable house for the money, a spacious backyard, and a small carport with storage area at the rear.
It's how they did it in the 1920s and earlier...with a few tweaks. The houses are 45x45' American Foursquares with five-foot-deep front porches (making them deeper makes them shadier at the expense of backyard space) set on a 50x100' lot. They have been placed asymmetrically, in order to provide side access on one side. A tiny amount of green space on the other side of the lot detaches the structures, since detached structures still have a price premium.

The alleyway is 10 feet wide, and the streets 30. This 30 feet is here translated into two 8' auto lanes (either both for travel or one for travel and one for parking) and two 7' sidewalks. You can go up to 50' in this design and use three 10' auto lanes (travel and parking) and two 10' sidewalks, or you could go narrower still and utilize naked streets.

This site design is easily adaptable, too. By switching out what we think of as proper "streets" with Radburn-style greenways, with the frontage side facing a 9' footpath with 7' access sidewalks, the rest of the former street space is converted into some small front (or side) yards. Thus, depending on frontage type and street width, this type of neighborhood can be optimized for (a) New Urbanism in a lower-density transect, (b) Landscape Urbanism (the Garden City), (c) streetcar suburbia, or even (d) autocentric suburbia. And since it's a '20s-type product, the results are already a pleasant known.
Notice how small the amount of auto facilities is needed for adequate service--just 250 square feet of alleyway and 400 square feet of carport.
But narrow streets are a key feature of the design. A 50-foot street width is barely tenable for a neighborhood street, and if the primary artery has a parking lane on each side, 60 feet would be the maximum allowable. Notice, too, how the way the houses are sited divides the site into a hierarchy of rooms: the street "room", the indoors "room", and the backyard "room". If the houses were sited any further back, the backyard would cease to be spacious and thus an amenity.

Finally, some population statistics. Each block (500x210') has 20 single-family detached houses. With the average family size of 4.3 (2 adults and 2.3 kids), this means the average block population is 46; since each block is (roughly) two acres, this gives a per-acre population of 32, which thence gives a per-mile population of 20,480 with 4,050 square feet a house* much of the U.S., an urban population with a large house size, and a population density more than enough to support transit.

How was this done? By narrowing streets and removing ornamental lawns. In a Radburn-like situation, where streets are only needed for vehicular access, even the ornamental lawns are restored while the mean density remains extremely urban.

So bad zoning and bad subdivision regulation is the problem. To put it bluntly: setbacks destroy backyards just as overly wide streets and overly restrictive single-use zoning** destroys place.
* 45 x 45 = 2,025 x 2 = 4,050. This includes neither basement nor attic. Foursquare assumes four 20 x 20 rooms per floor, linked together by 5-foot-wide hallways and closet areas. Eight 20 x 20 rooms is quite spacious for most families.

Secondly, consider if this setup were twins instead. Per-family living area decreases to 2,025 sf plus half a cellar and half an attic (gross 2,025 sf), but the per-block, per-acre, and hence per-mile population densities would all double, now to 40,960 per square mile. Storage shed space would need to double, thus reducing one twin's backyard space, but this would be by a mere 100 sf.
** Notice not Euclidean zoning. A lot of people confuse the two, but when done correctly, Euclidean zoning is extremely flexible and can even include some form-based elements. It can, in other words, be inclusive. By contrast, ORSUZ is inherently exclusive, and when combined with a subdivision code which mandates hierarchical street patterns and excessive street width, functions like place-destroying dynamite. It is a pity traffic engineers know so little about cities since they have unwittingly designed or redesigned so many of them over the past half-century.


  1. I'm sorry I missed this excellent post on the first go-around. Your asterisked comment about "twins" I think is very appropriate -- unless zoning restricted a neighborhood like this to single-family use, you'd quickly see many owners converting the second floors to rental units. In my former Nashville neighborhood which had many foursquares (and was zoned "duplex") this was a common, if not universal, practice. An alternative is to construct living quarters over the garage. What sort of zoning, if any, would you have in mind for a neighborhood like this?

  2. The average "family" size is not 4.3 people, so the density you cite is on the high side. It would be more realistic to expect about 3 people per house, especially in the duplex/twins version, leading to a max density closer to 25,000 people per square mile instead of 40k. The other thing to consider is the need for some retail and commercial space, parks, etc, which would bring the neighborhood density down to 20k or so, unless you provide a couple floors of apartments over the shops.

    But that's still a good density for frequent bus service or light rail or frequent regional/commuter trains, even with moderate car ownership of 1 to 2 cars per family.

    Many working neighborhoods in Los Angeles get this sort of density, though they usually have a 1-story house in front, with a two-story apartment building (with 4 units) in the location of the carports in this map, and lots of space devoted to parking instead of back yards. It's less pleasant, but it does provide 20 to 30k density (when mixed with some 2-storey apartment buildings and some retail strips)

  3. Charlie--I was thinking something along the lines of twins zoning (non-exclusive), something like R5 in Philadelphia's zoning code (see the Zoning Matters link in my right menu). Essentially, the model I'm working from is the type of housing you'll find in upper Manayunk, lower Roxborough, and University City (with varying degrees of attachment and ornateness).

    OTOH, the bare-bones carport does inhibit its use as granny flats, although I think the size of the homes being provided makes up for that. Garrett apartment, maybe?

    Joseph--Thanks for the correction. I was guesstimating based on a nuclear family of 2 parents and 2.3 children...but that's the Baby Boomer level, not today's level. Something closer to 2.5 or 2.7 people per dwelling unit might be closer.

    In any event, the further you subdivide the space (and there's plenty of space to subdivide) the higher the population density of the neighborhood is. Secondly, this was primarily conceived due to some posts a little while ago on Charlie's blog, and my main intent was showing how to incorporate an attic with a carport into site design without sacrificing the backyard (namely, by sacrificing the front yard). The assumption is that the commercial space is concentrated on main streets running through the neighborhood and/or dividing neighborhoods from one another...a structure found in many American cities.

    In my Triangle City post, I show how this residential design becomes a city for 50,000 souls in 2 sq mi.

  4. On the drawing those homes look small, but 45x45 is no joke.

    Funny thing about detached / semi-detached / rowhomes. I'd rather live in a proper rowhome than a twin (or semidetached in this rendering). The latter just seems like a cheap compromise. I'd gladly lose a couple feet of width on the second side (or trade it for backyard space) to make these fully detached houses.

    If your neighbor is a deadbeat (or literally dead, per Sunday's Inquirer) there's just too much that can go wrong with sharing a wall.

    The parallel park carport is genius. Never seen that before.

  5. Matt...These are designed to be SFD houses to fit the R1 classification in the zoning code (less setbacks), if the lot is 50x100. At that size, they are indeed generous (think Germantown big). Alternatively, they can be split into R5-type twins or even R10-type multifamily housing of two to four units. Because of how big each individual structure is, the neighborhood can handle quite a bit of densification before overcrowding starts to set in.

  6. I'm not sure where you guys are getting these density numbers from... the easiest way to calculate the density is as follows:

    Area associated with each house (includes half the width of the street and half the width of the alleyway):

    (100+15+5)*50= 6000 square feet

    One square mile is 27,878,400 square feet

    27,878,400 square feet per mile/6000 square feet per unit = 4646 units per square mile.

    Multiply that by 2.7 people per unit and the population density is 12,545 per square mile. Factor in schools, retail and parks and you get something around 7,000-10,000 per square mile which is pretty low density. I'm from the Toronto area and the new subdivisions in Toronto's suburbs are typically 12,000-18,000 people per square mile.

    [url=,+ON&hl=en&ll=43.550338,-79.747107&spn=0.0172,0.038581&sll=43.466702,-80.340055&sspn=0.273095,0.617294&vpsrc=6&t=h&z=15&layer=c&cbll=43.550338,-79.747107&panoid=_S1XW_seN_p-qBdHWcqpbQ&cbp=12,224.5,,0,-0.9]Here's [/url]an example of such a subdivision.

    If you want densities high enough to support quality transit and retail within walking distance, say 25-30k ppsm, you'd have to have lots around 1800 square feet. I would propose something like a 30x60 lot with a footprint of 26x30 sqft for the house which would have 3 stories plus a basement, and a 400 sqft garage or carport. That would give 1940 sqft of living area not including the basement or garage, 4 ft separating it from adjacent houses and a 30x30 sqft backyard. You could have a 20ft street with no front setback (or maybe a small front setback but a narrower street or slightly smaller backyard).