Infill

Infill Definition

Infill is the construction of new buildings in underutilized or vacant land lots within urban areas. Infill development is part of "smart-growth" policies to promote densification and the use of existing infrastructure. This is because many cities in the US have an abundance of parking and/or vacant lots that are well-connected to resources such as water, gas, transportation, and emergency services. Infill requires less land conversion, less space, and has the potential to supply new housing and services while decreasing the distances between places.

Infill development addresses several issues. Suburban sprawl or fringe development has resulted in greater land conversions from green areas or agricultural plots. Major land conversions (from green to urban) lead to environmental degradation and ecosystem disruptions. Additionally, housing stock and affordability are increasingly concerning and cities are seeking to remedy concerns through new construction. Additionally, infill development can increase the local tax base and attract new residents to the city.

Urban Infill History

Before understanding infill, it's important to understand how US cities ended up with so many vacant lots in their cities.

Parking Lots

There are different kinds of vacant lots in the US. By some statistics, there are eight parking spots for every car, comprising 5% of all urban land use.² The US expansion of parking lots follows the expansion of car use. After WWII, both the federal government and cities promoted car use and ownership, especially for new, affluent, and primarily white suburban commuters.

Because suburban residents still needed to commute to cities, major highways were built cutting through cities toward major employers. To further accommodate them, the majority of cities mandated parking requirements at a time of little data when it came to parking. This meant requiring developers and businesses to accommodate cars with arbitrary figures, which at times developed into situations where parking lots are three times the size of buildings.²

Fig. 1 - Vacant Lots and Surface Parking in Central Business District (CBD) in Houston, Texas, Map Data: © 2022 Google; this map doesn't include all the parking garages!

Currently, parking requirements are still mandated in most zoning codes. Meanwhile, some cities have reduced or scrapped parking requirements altogether because they usually increase housing costs and use the land inadequately. Despite zoning changes, many cities have an abundance of surface parking from decades of enforcement.

Vacant Lots

Vacant lots, or unused plots of land, have been found to reduce property values for the entire neighborhood.³ This is in part due to the emotions surrounding urban blight. It invokes the feeling that a place is run-down or abandoned and is headed for decline. Further, these lots decrease tax revenue, while increasing maintenance costs.

There are multiple reasons for these lots. Since the decline in manufacturing began in the 1960s, many industrial cities (especially in the north) saw populations decrease, with investment and tax bases moving elsewhere. Redlining practices further hampered investments that could have been made by minority groups that remained in inner cities.

The 2008 Recession disproportionally affected minority groups again, as predatory lending practices led to foreclosures and evictions resulting in higher vacancy rates for homes and units.³ For instance, cities like Detroit, Flint, and Gary, which have high Black resident populations, also have the highest rates of vacant units in the US.⁴

Infill Development Types

There are different types of infill development that can take place, depending on the size of the lot and the project goal.

Residential Development

In residential development, the aim is to increase the housing stock in the area. It usually includes multi-family units (i.e., duplexes and townhomes) focusing on densification in the area. These kinds of units are referred to as missing middle housing. These housing types were built prior to WWII but in recent decades have not been and are, therefore, "missing." They are typically affordable for low- and middle-income families.

Fig. 2 - Missing Middle Housing Types. These housing types are usually built during infill development

Mixed-Use and Transit-Oriented Development

Mixed-use development is a building with a mix of residential, commercial, entertainment, and other uses. While mixed-use can be applied on a building, block, or street level, usually a singular building with multiple uses is planned using infill. The mixed-use infill is to have homes and services in close proximity to each other which maximizes walking and public transit use.

Transit-oriented development can benefit from already existing infrastructure and services within cities. Any type of dense housing or mixed-use development within 800 meters of a public transit stop can be considered transit-oriented.

Occupied Lots: Brownfield and Greyfield Development

Some abandoned lots may already have existing structures and buildings. Brownfields are previously commercial or industrial areas that are underused or abandoned and may have issues with contamination. Brownfield development will usually require clean-up and site treatment to be deemed safe to use.

Greyfields are similarly underused or abandoned buildings that were previously commercial or retail spaces. Unlike brownfields, greyfields usually don't have contamination issues but may need investment to replace or renovate buildings.

Infill Housing: Barriers and Critiques

There are a few documented barriers and critiques to infill development, especially housing development. Community members perceive infill as inviting noise and traffic, as well as lowering property values. Because some cities waive parking requirements, local residents fear parking competition for remaining spots. Although some concerns are valid, most of the evidence on infill housing development indicates that property values increase after construction.⁴

However, this comes at a cost. Developers tend to set property values at higher rates to collect greater revenue.⁵ This can hinder the goal of providing affordable housing and may require greater government involvement in planning processes.

Fig. 3 - Infill Development. The aesthetic architecture of infill development should match the surrounding character of the area

Urban Infill Examples

Urban infill projects range in size from small housing units within a single plot to major redevelopment projects with thousands of acres of land.

Oakland, California

Oakland is experiencing issues of housing affordability and displacement due to gentrification. Historically, Oakland was a site for redlining, which until the 1970s prevented Black and other minority residents from obtaining home loans and financing. Without financial services available, urban decay took place in the form of abandoned lots and homes.

As part of a solution to address gentrification, the city is investing in its affordable housing stock. A recent housing project was Madison at 14th Apartments, built over a former surface parking lot in the city. It has mixed-use elements, with shops and restaurants at the street level. It provides affordable housing while also offering services to former foster care youth.

Central Park, Denver, Colorado

Stapleton International Airport was previously Denver's main airport hub until 1995 when Denver's International Airport opened. This provided over 4,500 acres left for redevelopment from the old airport. The Stapleton Development Foundation was founded to plan a new community with diverse housing options. A mix of office, retail, and parks are distributed throughout with high-quality pedestrian infrastructure to promote walkability.

It's one of the largest infill projects in the US, and has received awards from the Environmental Protection Agency (EPA) and the Stockholm Partnerships for Sustainable Cities Award given by the King of Sweden. The reuse of existing infrastructure and infilling of unused areas provides a great example of greyfield infill development.

Fig. 4 - Stapleton International Airport, Denver (1966). Over 30 000 residents now live in an area that was previously an airport