7 towers that define the 'skinny skyscraper' boom [slideshow]

Recent advancements in structural design, combined with the loosening of density and zoning requirements, has opened the door for the so-called "superslim skyscraper."

From New York to Melbourne to Vancouver, developers are planning high-rise structures on postage-stamp-sized parcels (OK, not that small, but we're talking lots as narrow as 22 feet) in dense urban locations.

Developers love the building type because they can finally take advantage of land that was previously unusable for large multifamily and mixed-use structures.

Some projects, like the Beach & Howe Tower in Vancouver (see No. 2 below), utilize a narrow form to accommodate multiple structures on a given site.

To be considered "superthin" or "slender," a tower must have a height-to-width ratio of at least 10:1. A typical skyscraper, such as the Willis Tower, falls in the 7:1 range. The new crop of skinny towers blows those ratios out of the water. For example, the 111 West 57th Street project in New York City has a height-to-width ratio of 22.5:1.

Here's a quick look at some prominent skinny skyscraper projects in the works:

1. 111 West 57th Street, New York

Building Type: multifamily (100 units)
Height: 1,350 feet, 77 fours
Width: 60 feet

Building Team
Developer: JDS Development
Architect: SHoP Architects
Structural engineer: WSP Cantor Seinuk

More on 111 West 57th Street via CTBUH's Skyscraper Center

2. Beach & Howe Tower, Vancouver

Building Type: multifamily (407 units)
Height: 493 feet, 49 floors
Width: NA

Building Team
Developer: Westbank Corp.
Architects: Bjarke Ingels Group (BIG), James KM Cheng Architects
Structural engineer: Glotman Simpson Group
MEP engineer: Cobalt Engineering

More on the Beach & Howe Tower via CTBUH's Skyscraper Center

3. Phoenix Apartments, Melbourne, Australia

Building Type: multifamily (28 units)
Height: 290 feet, 29 floors
Width: 21 feet, 11 inches

Building Team
Developer: Equiset
Architect: Fender Katsalidis Architects

More on the Phoenix Apartments via Sidney Morning Herald

4. One57, New York

Building Type: mixed use, with hotel (210 rooms) and multifamily (92 units)
Height: 1,005 feet, 79 floors
Width: NA

Building Team
Developer: Extell Development Company
Design architect: Christian de Portzamparc
Executive architect: SLCE Architect LLP
Structural engineer: WSP Cantor Seinuk
MEP engineer: AKF Engineers
Exterior performance consultant: Israel Berger Associates
Interior designers: Yabu Pushelberg (hotel), Thomas Juul-Hansen, LLC (residential)
Contractor: Bovis Lend Lease

More on One57 via CTBUH's Skyscraper Center

5. 464 Collins Street, Melbourne

Building Type: mixed use, with multifamily (37 floors, 185 units) and office (13 floors)
Height: 593 feet, 50 floors
Width: 36 feet, 1 inch

Building Team
Developer: Equiset
Architect: Bates Smart

More on 464 Collins Street via Urban Melbourne

6. 432 Park Avenue, New York

Building type: multifamily (125 units)
Height: 1,397 feet, 85 floors
Width: 50 feet

Building Team
Developers: CIM Group, Macklowe Properties
Architects: Rafael Vinoly Architects, SLCE Architects
Structural engineer: WSP Cantor Seinuk
MEP engineer: WSP Flack + Kurtz
Contractor: Bovis Lend Lease