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It must be said that "the invention of agriculture made cities possible."
Urban Sprawl vs. Prime Farmland
A primary reason a place is called a "city" is its large human settlement. It is a densely settled area with administrative boundaries, in which members work primarily on non-agricultural tasks.
Ever since 1950, the income in the United States was much more evenly distributed, and the "Big Three" (General Motors, Ford, and Chrysler) continued to prosper: producing three-quarters of all automobiles in the world. This revolution incentivized huge populations to move to suburbia and enjoy more extensive land per household. Their car-dependent lifestyle increased "urban sprawl," a vocabulary first appeared in 1955.
However, the major problem of urban sprawl is the reduction of prime farmland. In 2019, the total agricultural land, at 897,400,000 acres, decreased 2,100,000 acres from 2018. Over the last eight years (2012-2019), 17,200,000 acres of farmland have been lost nationwide. That is equivalent to losing 245 acres per hour. (1)
Smart Growth: 10 Principles to Manage Urban Sprawl
The loss of prime farmland will inevitably influence our food supply and other services. So how to reverse this "urban sprawl" trend?
In 1996, the Smart Growth Network (SGN), initiated by EPA and other organizations, developed ten smart-growth principles (2). Among them, "mix land use" and "range of housing opportunities and choices" impact how we shape our urban neighborhoods the most.
Often, we have this preconceived notion that "high density" equals high-rise buildings or a crowded neighborhood. But more precisely defined, the higher density means new development at a higher density than the typical existing context.
Therefore, I want to introduce several typical housing types to understand one of the essential elements of smart growth.
A Range of Housing Types and Density
Here are some of the common dwelling types:
Townhome /Rowhouse,
Garden apartment,
Four stories wrap
Four/Five stories over the podium
High-rise residential tower
A townhouse generally shares the following characteristics:
This type incentivizes residents to live in an area that provides amenities with lower maintenance costs.
Even with a higher density than typical single-family houses, the building gives "village" characteristics. Each household can still enjoy a private patio on their lot.
The image above is one example with 13 DU per acre, with an average of 3 bedrooms units.
[This density range is equivalent to a habitat of 24,200 people per square mile and could achieve 1 point for Compact Development credit in LEED-ND.]
Here are two typical layouts as a good reminder when we choose this housing type:
This one allows service routes separate from pedestrian walkways and regular vehicle traffic. It is easier for service trucks to get in and out of the development site without disturbing the primary traffic.
This one mixes service routes with regular traffic. It provides a better quality of back yards, but all the loading and trash go out from the front entrance, creating noise or other issues. It also limits some walkability during a particular time of the day.
Garden apartments are considered "typical" for higher density of suburban neighborhoods. It has the following characters:
The development is often formed as a court pattern or clustered around amenities.
This typology often comes with walk-up or open stairways to lower the average construction cost and minimize mechanical maintenance.
Most open spaces of this type are used for surface parking and circulation.
The image above is one example with 18 DU per acre, with an average of 2 bedroom unit.
[This density above is equivalent to a habitat of 22,900 people per square mile and could achieve 2 points for Compact Development credit in LEED-ND.]
Four-stories wrap is also known as "Taxes Donut": a four-story wood construction around a central parking garage. This scenario offers the following features:
Type 5A wood constructions for dwelling units to shorten construction time.
Providing on-site parking spaces with a multi-level parking structure at the center.
Allowing dwellings to happen at the pedestrian level.
The image above is one example with 91 DU per acre, with approximate 41% of one bedroom and 40% of two bedroom units. Its layout was morphed from the typical single "loop wrap," thus creating internal courtyards for views and lights.
[the density above is equivalent to a habitat of 58,200 people per square mile and could achieve 6 points for Compact Development credit in LEED-ND.]
Four/Five stories over the podium are popular in many mixed-use projects. It has the following features:
Multi-levels of wood-frame/light-frame structure over a concrete podium.
By elevating the interior courtyard, residents can have internal views regardless of the surrounding site condition.
Commercial and retail uses are allowed at the podium level, with more extensive and transparent fenestrations at the pedestrian level.
The building is often perceived as massive or bulky and lacks local contextual characters.
The image below is one example with 148 DU per acre, with an average of one to two bedroom units.
[This kind of density is equivalent to a habitat of 95,000 people per square mile and could achieve 6 points for Compact Development credit in LEED-ND.]
High-rise residential towers became popular after the 1950s when many cities tried to meet the housing demand. (3)
It gives the most density per occupied building footprint.
Parking spaces could be integrated as part of the building massing.
Commercial and retail uses are often allowed in the same building and offer various on-site services.
Its height and bulk have the potential to function as a landmark for the neighborhood.
This type of dwelling has the highest construction cost per square foot.
The image below is one example with DU per acre, with an average of 2+ bedroom units.
What’s the takeaways
By providing housing types that offer a wide range of economic levels, household sizes will enable a more equitable community. Use Simpson Diversity Index to determine if the neighborhood has provided an adequate mixture of housing types. Strategically blending these housing types along a transit corridor will help conserve land, leverage, and support transit investment.
Notes and Reference:
Farmland data excerpt from “Farms and Land in Farms, 2019 Summary”, February 2020, USDA
Those organizations included real estate, environmental, development, affordable housing, government, etc. The ten principles are as follows:
Mix land use
Compact building design
Create a range of housing opportunities and choices
Walkable neighborhoods
Foster a distinctive, attractive community with a strong sense of place, preserve open space, farmland, natural beauty, and critical environmental areas.
Strengthen and direct development towards existing communities.
Provide a variety of transportation choices
Make development decisions predictable, fair, and cost-effective.
Encourage community and stakeholder collaboration in development decisions.
For more details, check out Smart Growth Network from Environmental Protection Agency
The complete table of LEED ND credit “Compact Development” by comply the density below.
A Simpson Diversity Index Score can be calculated as follows:
Score (D) = (n / N)2.
A useful table determining housing diversity can be found in LEED-ND credit: Housing Types and Affordability
* Based on IBC’s definition, the “High-rise Building“ means “a building with an occupied floor located more than 75 feet above the lowest level of fire department vehicle access.“ Therefore, many 8-stories building will considered an a “High-rise Building“.
* “High-rise residential tower” listed is is to distinguish a high-rise building with more than 8-stories in height.
Do not get confused by the density requirement in zoning code with the density that a certain housing type normally offers. For example, in Montgomery County, R-30 is residential low density zone with 14.5 DU per acre, R-10 is residential high density zone with 43.5 DU per acre. Choose the housing type according to the desired open space to meet specific zoning requirement.