Across the globe, people are migrating to cities to live and work. The United Nations says 3.9 billion people — 54 percent of the world — live in metropolitan areas. By 2050, 66 percent of all people will be city dwellers, which means an extra 2.5 billion people will need urban housing.
The boon in urban development is also well underway here in the United States. Nearly one-third of all Americans live in one of the 10 most populous cities. Overall, 89 percent of American economic growth takes pace in metro areas.
With that in mind, what should designers, developers, and builders know about the brave new world of urban development?
New infill guidelines
Many American cities have issued ordinances related to urban infill development. Narrow-lot zoning and the formation of special city agencies allow architects, developers, and builders to create more urban townhomes, row houses, and cottage courts.
Los Angeles passed a successful small lot ordinance in 2005. Where 5,000-square-foot lots once had to be used for single-family homes or condominiums, LA’s Small Lot Ordinance No. 176354 opened the options on how small lots could be developed.
In 2014, the Los Angeles Department of City Planning published the Small Lot Design Guidelines. The handbook outlines what’s expected of designers and developers. For example:
- Small lot homes must be structurally independent with no shared foundations or common walls.
- Projects must use existing topography and maintain grade levels consistent with surrounding structures.
- The proximity of structures requires innovation related to massing, height, and transitional areas.
Of course, some local activists are challenging Los Angeles’ approach to urban infill development. Nevertheless, the City of Angels remains a model for how designers, developers, builders, city planners, and community members can work together to develop the urban landscape.
The question is, can any building materials contribute to urban infill project success?
An ideal framing material
Narrow-lot zoning gives designers, developers, and builders some leeway in choosing building materials for projects. But stakeholders should carefully consider their choices. Some building materials, such as cold-formed steel (CFS) framing, can contribute significantly to the creative use of tight spaces.
Here are three reasons why CFS is an effective framing choice for infill projects:
1. CFS is strong and lightweight
Since CFS is sometimes referred to as light-gauge steel, designers, developers, and builders may think it’s suitable only for interior drywall partitioning and for framing low-rise structures.
However, CFS offers exceptional strength. Load-bearing CFS commonly supports mid-rise buildings up to 10 stories — although some professionals argue it can support a building as tall as 40 stories.
City Green, a 135-unit residential building in Milwaukee, sits on a 1.2-acre hill in a T-shaped lot. The developer’s design included three CFS-framed towers and preserved 126 revenue-generating parking spaces for the city.
“Architects might not realize that cold-formed steel studs are this strong,” said Patrick W. Ford, P.E., Principal, Matsen Ford Design. “The exterior walls can support nine stories and steel balconies.”
CFS is also lightweight, a key consideration for inner-city projects. Compared to concrete, lightweight CFS framing reduces building load. CFS-framed structures can achieve cost savings on footings and foundations.
And, lightweight CFS framing is an effective solution when adding stories to existing structures. For example, consider Piatt Place in downtown Pittsburgh, which was originally a four-story department store. To expand urban living availability, the general contractor needed to add three stories on top of the existing building to house upscale condominiums. CFS was the natural choice for this project, as it minimized the additional weight on the existing foundation and allowed the owners to construct the condominiums at prices acceptable to the market.
2. CFS is noncombustible
As urban planners see their cities becoming denser and denser, many have concerns about fires — and those worries aren’t misplaced. A few recent fires in the United States have destroyed several wood-framed buildings.
A January 2015 fire at the Avalon, a mid-rise building in Edgewater, New Jersey, displaced about 500 tenants and affected neighboring residents. Lawsuits filed against the building owner charge that “the risk of fire during construction and for maintenance was known, and that risk is increased when using lightweight wood construction.”
A fire in February 2017 destroyed a Maplewood, New Jersey apartment building from the same developer as the Avalon. NorthJersey.com reported that the Maplewood blaze prompted more calls to change New Jersey’s building code to limit the use of lightweight wood construction.
“Why are we waiting?” asked Glenn Corbett of Waldwick, an associate professor of fire safety at John Jay College in New York and quoted on NorthJersey.com. According to the story, Corbett would like to eliminate lightweight wood construction on all projects above three stories.
The Atlanta suburb of Sandy Springs is working to ban combustible framing above three stories. “The concern is, nationally, the fact that lightweight wood-frame construction is very dangerous to the firefighters when a fire ignites,” said Sandy Springs Fire Rescue Chief Keith Sanders, quoted by Atlanta Public Broadcasting station WABE 90.1.
In contrast to wood, CFS is noncombustible, and CFS-framed buildings can reduce the stress placed on municipal fire services and the communities they serve. This makes CFS an ideal framing material for urban infill projects.
3. CFS panelization lowers the construction impact on neighborhoods
Panelization has many benefits. Prefabricated CFS assemblies deliver speed, quality control, and low community impact in several ways.
First, CFS is a predictable material. CFS wall panels, flooring joists, and trusses can be assembled precisely, delivered to the job site in timely fashion, and erected quickly. This allows follow-on trades to start their work sooner. Compared to concrete, CFS panelization cuts time from the construction cycle.
In addition, CFS walls, flooring systems, and trusses can be fabricated in controlled shop conditions. The panelization process minimizes weather delays and ensures greater quality in comparison to wood framing, since wood tends to absorb moisture and swell.
Finally, CFS assemblies can be delivered quickly to a job site and often installed on the same day. This lowers the amount of space needed to stage framing materials on site or on the street, lessoning the impact on the neighborhood.
The urban landscape is a complex place to develop and build structures. But city after city has shown that urban infill development can work.
Within eight years of passing its Small Lot Ordinance, Los Angeles has seen over 160 subdivision cases filed, over 1,500 individual lots approved, 39 subdivisions recorded, and 330 new lots added to the county assessment roll.
Certainly, infill development is an exciting area of urban planning. But remember, the choice of building material helps to achieve good results. If you have questions or would like assistance on a CFS-framed project, request complimentary project assistance from our team of experts.