Ever run into the word 'diagrid' and wonder what it means? This week's Explainer delves into this specialized structural framework, in use since the late 19th century. Although the building method was not originally popularized, diagrids are popping up in many modern projects all over the world today. So, why do some buildings use diagrid structures, and how is it unique to other frameworks?

30 St Mary Axe in London, image by Marcus Mitanis

A portmanteau of diagonal grid, the diagrid is a visible architectural element of several recent world-famous buildings. Beyond its eye-catching aesthetic value, the framework of diagonally intersecting metal, concrete, or wood yields structural benefits. Providing strength and stiffness to buildings, particularly those with complex geometries, a diagrid framework requires less structural steel, by up to 25 percent, than a conventional steel frame.

Hearst Tower in New York City, image by Marcus Mitanis

The diagonal members support gravity loads and lateral forces instead of the usual vertical columns. Buildings that utilize the diagrid system are generally free of intrusive interior columns, giving way to large and open floor plans. When the steel members are sheathed in glazing, it not only highlights the unique structural elements of the building, but creates an environment with an abundance of natural light.

The Bow in Calgary, image by Flickr Antoine 49 via Creative Commons

The diagrid system, however, is arduous to implement; complicated computer models and construction methods require experienced engineers, architects, and contractors. For steel diagrid structures, the prefabrication process can add significant costs to the project. Similarly, concrete diagrid structures require a vast amount of formwork. 

Award-winning British architect Norman Foster has earned a global reputation for his firm's diagrid-rich designs. The Hearst Tower in New York City — which utilizes 21 percent less steel than a typical design — is one of the most famous examples of a diagrid framework. Two of Foster's other designs, 30 St Mary Axe in London and The Bow in Calgary, are among their other most lauded works. In Toronto, Foster + Partners' design for The One does not feature a diagrid, but its design shares some of the principles of diagrid design through the "hangers" that support the corners of the building, their loads supported from the perimeter supercolumns.

The One in Toronto, does not have a diagrid structure, but shares some principles with diagrid design, image courtesy of Mizrahi Developments

Have any other construction and development related terms that you would like to see featured on Explainer? Share your thoughts and questions in the comments section below!

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From 2015 to 2017, UrbanToronto and its sister publication, SkyriseCities, ran an occasional series of articles under the heading Explainer. Each one took a concept from Urban Planning, Architecture, Construction, or other topics that often wind up in our publications, and presented an in depth look at it. It's time to revisit (and update where necessary) those articles for readers who are unfamiliar with them. While you may already know what some of these terms mean, others may be new to you. We are publishing or updating and republishing Explainer on a weekly basis. This article is an update of one by Marcus Mitanis that was originally published in 2017.

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Do you have other planning terms that you would like to see featured on Explainer? Share your comments and questions in the comments section below!

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