Street and block

In the second week, Adeyemi pins four maps side by side on the studio wall, all at the same scale: the blocks around the studio site, a piece of central Barcelona, a piece of Portland, Oregon, and a suburban office park on the edge of the city. 'Same scale, four worlds,' she says. 'Count the intersections a person passes in a ten-minute walk on each map. Count the buildings that touch the sidewalk. Then tell me which one you would want to walk through in February.' The office park has three intersections in ten minutes and no building within 100 ft of the road. The warehouse district has more than twenty. This lesson is about streets and blocks, the frame that every urban building fills.

Streets as public rooms

A street is not just a channel for traffic. It is the city's largest public space, the place where people walk, meet, shop, wait, play and protest. The width of a street, the height and continuity of the buildings along it, the activity in their ground floors, the trees, lights and furniture on the sidewalk, all shape how it feels to be there. Urban designers often describe a good street as an outdoor room: its walls are the building fronts, its floor is the sidewalk and roadway, and its ceiling is the sky.

The proportion of that room matters. A common measure is the ratio of building height to street width. When buildings are about as tall as the street is wide, a ratio near 1:1, the street feels enclosed but not oppressive, like many of the best streets in historic European and North American cities. At ratios much lower than about 1:3, as along a wide arterial lined with one-story stores, the street loses its sense of enclosure and feels like a highway. At ratios much higher than about 2:1, as in the canyons of a dense downtown, it can feel dark and windswept, and winter sun never reaches the sidewalk.

# Enclosure of the streets around the site: height-to-width ratio
streets = {
    # name: (building height on one side, height on the other side, width between building faces) in ft
    "the avenue": (90, 66, 86),
    "Tessier Street": (90, 40, 66),
    "back lane": (53, 38, 20),
    "arterial at the edge of downtown": (16, 15, 130),
}
for name, (h1, h2, w) in streets.items():
    ratio = (h1 + h2) / 2 / w
    if ratio < 0.33:
        feel = "open, little enclosure"
    elif ratio <= 1.5:
        feel = "enclosed, comfortable"
    else:
        feel = "canyon-like"
    print(f"{name:34s} average height {(h1 + h2) / 2:5.1f} ft, width {w} ft, ratio {ratio:.2f} -> {feel}")

the avenue                         average height  78.0 ft, width 86 ft, ratio 0.91 -> enclosed, comfortable
Tessier Street                     average height  65.0 ft, width 66 ft, ratio 0.98 -> enclosed, comfortable
back lane                          average height  45.5 ft, width 20 ft, ratio 2.27 -> canyon-like
arterial at the edge of downtown   average height  15.5 ft, width 130 ft, ratio 0.12 -> open, little enclosure

The avenue, once the studio building is in place, will have a ratio of about 0.9, close to the comfortable 1:1. Tessier Street will be a little more enclosed. The back lane is narrow and tall, a canyon, but lanes are service spaces where enclosure matters less, and a canyon-like lane can still be pleasant if it is well lit and the buildings along it have doors and windows. The arterial at the edge of downtown, lined with low strip malls, is wide open, and it is no surprise that nobody walks there.

Anatomy of the sidewalk

The space between the curb and the building front has its own structure. Urban designers divide it into zones, each with a job.

• The frontage zone, nearest the buildings, where café tables, sandwich boards, planters and door swings belong, and where people pause to look in windows.
• The pedestrian through zone, kept clear for walking, at least 6 to 8 ft wide on a busy downtown street so that two wheelchairs or two groups can pass.
• The furnishing zone, along the curb, holding trees, light poles, benches, bike racks, bus shelters, signs and, in winter, the snow piled by plows.
• The edge or curb zone, where people step into and out of vehicles, buses and bike lanes.

The sidewalk along the avenue in front of the site is 15 ft wide from the property line to the curb. That allows a frontage zone of about 3 ft, a clear walking zone of about 8 ft and a furnishing zone of about 4 ft. The building owns none of it; the sidewalk belongs to the city. But the building decides how the frontage zone is used, whether doors open onto it, whether a canopy shelters it, whether café tables spill into it and whether windows invite people to linger. A blank wall makes even a wide sidewalk feel empty; a row of open shopfronts can make a narrow one feel generous.

Blocks

Streets frame blocks. The size of a block determines how many routes a pedestrian has, how often they reach a corner, how many buildings can face a street and how lots can be subdivided. Small blocks of about 200 to 330 ft on a side, like those of Portland's downtown, which measure about 200 feet, give a fine-grained, walkable network with many corners and short walks. Large blocks of 650 ft or more force long detours and tend to fill with large single buildings or parking. Studies of walking in North American cities consistently find that the density of intersections, which rises as blocks get smaller, is one of the strongest predictors of how much people walk.

The blocks of the Minneapolis Warehouse District are irregular, shaped by the rivers, the railways and early land surveys, but most are between 260 and 430 ft on a side, with lanes running through them. The lanes are an important feature: they let deliveries, garbage and parking reach the backs of buildings without crossing the sidewalks, leaving the street fronts free for doors and windows.

# Walkability of four block patterns over the same area (one square mile)
import math
area = 27878400                                   # square ft in one square mile
patterns = {
    # name: (block length, block width, street width), all in ft
    "Portland downtown": (200, 200, 66),
    "warehouse district": (394, 295, 80),
    "Barcelona Eixample": (371, 371, 66),
    "office park superblock": (1312, 984, 100),
}
for name, (a, b, s) in patterns.items():
    cell = (a + s) * (b + s)                    # one block plus half the streets around it
    blocks = area / cell
    intersections = blocks                      # one intersection per block on a regular grid
    street_share = 1 - (a * b) / cell
    frontage = blocks * 2 * (a + b)             # length of block edge facing streets
    print(f"{name:24s} {intersections:6.0f} intersections, streets take {100 * street_share:4.1f} of every 100 ft2, "
          f"block frontage {frontage / 5280:5.1f} miles")

Portland downtown           394 intersections, streets take 43.5 of every 100 ft2, block frontage  59.7 miles
warehouse district          157 intersections, streets take 34.6 of every 100 ft2, block frontage  40.9 miles
Barcelona Eixample          146 intersections, streets take 27.9 of every 100 ft2, block frontage  41.0 miles
office park superblock       18 intersections, streets take 15.7 of every 100 ft2, block frontage  15.8 miles

The calculation shows the trade-offs. Portland's tiny blocks give about 400 intersections per square mile and the most street frontage, the most places for doors and shops, but streets take up more than two-fifths of the land. The office park has fewer than twenty intersections in the same area and about a quarter of the frontage. The warehouse district and Barcelona fall between: enough corners for an easy walk, enough frontage for continuous shops, and enough land inside each block for buildings with courtyards. Cerdà's Eixample, laid out in the 1860s, added another refinement: chamfered corners that widen every intersection into a small plaza, a feature that the corner of the studio site could echo in miniature.

Lots and grain

Within a block, land is divided into lots. Historic downtown lots were often narrow, 25 to 50 ft wide, because land was bought and built in small pieces; a warehouse might occupy two or three of them. The result was a fine grain: many buildings, many owners, many entrances and a constant variety along the street. Modern development tends to assemble lots into large parcels for single big buildings, which can be efficient but can also produce long, monotonous facades and a coarse grain.

The studio site was originally four lots of 33 ft each on the avenue, assembled and cleared in the 1960s for parking. Adeyemi asks the students to remember this. 'You may design one building, but the street should not read it as one undifferentiated block,' she says. 'Look at what forty meters of frontage looked like in 1915: four buildings, four doors, four rhythms.' The facade lesson will return to this question.

Corners

Corners are the most valuable and most visible parts of a block. They are seen from two streets and from a distance along each, they collect pedestrians from two directions, and they get light and air from two sides. In historic districts, corners held banks, hotels, taverns and shops, often with an entrance cut diagonally across the corner and a turret, dome or taller bay marking it. The studio site is a corner lot, and the corner of the avenue and Tessier Street is where its most public use and its most memorable form belong.

Corners also have practical rules. Cities often require a corner clear of tall objects so that drivers can see pedestrians, and they do not allow loading bays or garage entrances near intersections. Building at the corner usually means keeping the ground floor corner open and glazed, perhaps with a chamfer or a recess that widens the sidewalk where people wait to cross.

Lanes

The back lane is the building's service side. In the studio site's lane, garbage trucks collect from the Harland Building and the Coach House twice a week, delivery vans stop at the restaurants, and the artists in the Coach House load their work. The lane is where the studio building's loading, garbage and recycling, bike parking entrance and perhaps a few parking spaces should go, keeping the avenue and Tessier Street free of curb cuts.

Lanes can be more than service spaces. Several cities have improved lanes with paving, lighting, planting and small shops or studios that open onto them, turning them into intimate secondary streets. Minneapolis has improved several downtown alleys as shared spaces. For the Coach House artists, a lively, well-lit lane would be safer and more pleasant than a dark one. The students consider whether the Foundry Collective's workshop doors could open onto the lane, adding activity and allowing big deliveries.

Exercise 2: street and block studies

This exercise takes one week.

• Draw the four blocks around the site and three comparison districts at the same scale, and count intersections and frontage.
• Draw sections through the avenue, Tessier Street and the lane at 1/16 in = 1 ft, with the existing buildings and a placeholder for the studio building, and calculate height-to-width ratios.
• Design the sidewalk zones along both street frontages, including trees, bike racks, café space and snow storage.
• Assign every use in the brief to an edge of the site and justify the choice in a short diagram.

Self-critique checklist

• Have I drawn the street as a room, with both sides?
• Does the most public use face the busiest edge?
• Have I kept loading and garbage off the streets?
• Have I considered winter: snow storage, sun and wind on the sidewalk?