Urban Scale
Article
Urban scale is the term used to describe some of the most important characteristics of streets, including the perceived scale of the street vertically, the sense of enclosure within a “street room” and the degree of definition of the street and its addresses as a place. The term is defined as the height of the street wall relative to the width of the street, from street wall to street wall (building face to building face). Thus, urban scale is measured using the “height to width ratio” laterally across the street. The use of the term “urban” also suggests the importance of the overall context of an area, and the role neighboring buildings play in establishing a sense of scale. Groups of buildings and the spaces between them establish a high, medium, or low urban scale.
The urban scale of a “street room” has a major effect on how the street is perceived by motorists and pedestrians. Streets with high ratios of height to width feel urban and enclosed. There is a strong sense of spatial definition and enclosure that can be supportive to placemaking. However, streets with very high urban scale – greater than 3:1 – can begin to feel like “concrete canyons” and can be claustrophobic, especially along narrower streets. Such streets can be cold and harsh in winter. In the St. Louis region, as in many other parts of the U.S., such streets also can concentrate and redirect winds at sidewalk level in ways that are not conducive to a comfortable walking environment. In temperate climate zones, “sun access” can be another key issue in planning and design. On east-west streets with high urban scale, the sun may not reach lower floors of buildings during winter months. On high scale north-south streets, windows of buildings may receive little direct sunlight any month of the year.
The images at right illustrate the way in which buildings are grouped in various places to create a distinct urban scale. A downtown skyscraper district of a major city is clearly of a great or high urban scale. The buildings are tall, and often have substantial mass or girth.
An area with buildings predominantly between four (4) and eight (8) stories is typically considered to be of a medium scale; however the city context makes a difference. Eight stories might be considered a high-rise urban scale in a small city, whereas it could easily be thought of as a medium urban scale in a large city.
The image below, at left, is an example of medium urban scale, although these boundaries may vary by place. A one and two-story residential neighborhood, as shown in the image below/at right, includes predominantly low-height buildings, which establish a low urban scale. Increased horizontal spacing of buildings and the corresponding increase in space between buildings also contributes to the low urban scale.
The urban transect diagram shown in this PDF outlines the structure of typical urban settlement patterns, described using increasing increments of urban scale, or transect zones. The scale divides areas into six (6) transect zones, extending from T1 (rural preserve) to T6 (urban core). The figure also identifies a number of features that contribute to land use intensity and urban scale, such as setbacks, greenspace, lighting, and building materials.
The key to creating successful mixed-scale neighborhoods and districts, such as the one shown at right, lies in effectively transitioning between buildings and clusters of different scales. The appropriate relationship and transition between buildings and clusters should be outlined in a City’s building and design policies.
Specific development standards and design guidelines can help residents understand building policies and practices and provide developers with better guidance to facilitate approvals.
The figure at right depicts one example of a “form-based code” approach to setting height limits for a downtown district.
While form-based codes and height limits help establish a basis for urban scale, the architectural articulations of building height and massing largely influence the feel and urban scale of an area.
In addition to a building’s general dimensions, the articulation of the mass and facade play a critical role in defining urban scale. Buildings that lack traditional scale cues such as individual window openings and sills, visible stories, intermediate cornices, entryway features, or a building base may seem overwhelming and can be confusing with respect to scale.
For example, in the absence of the small brick side buildings in the photo at right, the actual height and scale of black glass cube building would be difficult to determine. When a large building has none or very few of the scale references listed above, it is said to lack human scale.
Buildings of extremely different heights and contrasting levels of articulation of scale (as shown at right) may create an unattractive and undesirable clash of scales that does not reflect well on either building, or on the district of which they form a part.
Misfit in urban scale, especially between low to medium scale residential buildings, as shown below, at left, can have a substantial negative impact on privacy, livability, real estate values, and neighborhood character.
With careful attention to design and articulation, large buildings can be visually broken down into smaller, more human-scaled components, as shown in the image below, at right.
Emphasizing the ground floor of a building can help create a more interesting streetscape and pedestrian environment, and sculpting back the mass of the building with upper level setbacks can help reduce the size and impact of the street wall.
In the photo at the right, Market Street in San Francisco is an example of a high scale street. Market is a major multimodal transportation corridor and one of San Francisco’s most important commercial streets. It also feels intensely urban. However, this effect is mitigated significantly through good design (including wide sidewalks that reduce the impact of the street) and by wide variation in building height up and down the street. Although San Francisco is at a similar latitude to St. Louis (37° 40’ compared to 38° 40’), it has generally a more moderate climate (especially in the winter) and thus the shading and loss of direct sun on this east-west street is less important than it might be elsewhere.
At the other end of the range, streets with very low urban scale – less than 1:4 – exhibit little spatial definition. Such streets feel similar to certain large ballrooms in hotels or meeting rooms in conference centers. Rooms that are, say, 120 feet from wall to wall with ceilings at 20’ or less are perceived not in their entirety but as a series of spaces defined by furniture, potted plants, dividers, even changes in floor covering. Streets are experienced in a similar manner (with the sky as ceiling).
Wide, low scale streets are perceived as a series of spaces with little coherence. The street walls (buildings) do not enclose and define the street enough for it to be perceived as a place. Placemaking along such streets is difficult and requires the use of other defining elements – trees, walls, and street furniture.
An example of a low scale street in the St. Louis region is shown in the photo on the right. Here there is no enclosure at all and the street appears almost rural, even though traffic is heavy and the adjacent land uses are all commercial. This kind of environment is almost completely intolerable for pedestrians.
The perceived urban scale of low scale streets can be increased through use of street trees. For example, the urban scale of the street in the photo on the right – Main Street in Pleasanton, California – is enhanced by the street trees that increase the perceived height to width ratio above what it would be if measured by the height of the buildings along the street.
Graphic representations of common height to width ratios and photos of corresponding examples are shown below. Generally, “great streets” will have urban scale ratios that fall in a range between 3:1 at the high end and 1:3 at the low end.
3:1 Height to Width Ratio (see examples below)
- Sense of spatial definition: strong; may feel like a “concrete canyon” in some settings
- Skyview: very narrow; viewing tops of buildings requires changing neck angle
- Lowest sun angle reaching bottom of north street wall at mid-day: 71° (east-west street)
3:2 Height to Width Ratio (see examples below)
- Sense of spatial definition: strong; clear sense of enclosure
- Skyview: limited; viewing tops of buildings requires changing neck angle
-
Lowest sun angle reaching bottom of north street wall at mid-day:
56° (east-west street)
1:1 Height to Width Ratio (see examples below)
- Sense of spatial definition: high, strong placemaking potential
- Skyview: limited, peripheral only
-
Lowest sun angle reaching bottom of north street wall at mid-day:
45° (east-west street)
1:2 Height to Width Ratio (see examples below)
- Sense of spatial definition: good; sufficient for placemaking
- Skyview: views of sky about equal to visual field occupied by street wall
-
Lowest sun angle reaching bottom of north street wall at mid-day:
27° (east-west street)
1:4 Height to Width Ratio (see examples below)
- Sense of spatial definition: weak; placemaking potential is low
- Skyview: three times as much sky as wall within normal range of human vision
-
Lowest sun angle reaching bottom of north street wall at mid-day:
15° (east-west street)
- Last Updated on Tuesday, 10 June 2014