The Notre-Dame Question


It's been about 4 weeks since the timber roof at Notre-Dame Cathedral in Paris burned on April 15. For me it was shocking and heartbreaking. (A small silver-lining: on that day I heard from several former students who loved the building too, and they reached out because they knew I'd be grieving.)

Almost as soon as the fire was extinguished, French president Emmanuel Macron announced that the cathedral should be rehabilitated very quickly, in time for the 2024 Summer Olympics. And Prime Minister Édouard Philippe announced a competition which will seek a new design for the roof and spire which is “adapted to technologies and challenges of our times.”

By April 19, Norman Foster put forth a vision for a new “light and airy” roof. Dominique Perrault said the problem is “extremely delicate” but that the rebuilding should create “an even more powerful presence, a wider resonance, transfiguring, amplifying, and exalting it into something else.” Vincent Callebaut has proposed a timber and glass urban farm. And plenty of other non-traditional design ideas have been offered.

Callebaut tributetonotredame_pl000.jpg

Now, with a bit of distance from the event, there are significant calls to slow down. More than 1000 signatories, including noted curators, architects, and art historians, asked French president Emmanuel Macron to wait to make major decisions about the cathedral’s future. Presumably they would like some consideration given to a traditional restoration. Nevertheless, the French assembly approved a law to move quickly, rebuilding Notre-Dame within five years.

What should be done? Rebuild traditional or modern?

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I will take students to Paris this summer, and we’ll grapple with the question of what should be done. As we discuss that question, here are some essential concepts to understand:

  • The timber roof was essentially a lightweight umbrella, to keep the weather off of the structure below. Structurally, it is an afterthought. The stone vaults are the true roof structure; their weight and thrust are what the flying buttresses are supporting and resisting.

  • Before the fire, Notre-Dame was hardly ‘original’. (I set off the word original because it’s such a fraught concept.) It was damaged extensively during the French Revolution, when the Gallery of Kings on the west facade was destroyed. Then for Napoleon’s in 1804 the exterior was whitewashed and the interior was remodeled in the neo-classical style.

  • The spire—flèche, in French—that burned and collapsed so spectacularly was relatively young, built in the 1860s in the seminal ‘restoration’ by Eugène Emmanuel Viollet-le-Duc. (Restoration, too, is a fraught concept, especially Viollet-le-Duc’s approach. Wikipedia has a good summary.) There was a medieval spire, built about 1250, which was removed in 1786 after wind damage. Viollet-le-Duc’s spire was taller than the 13th-century construction.

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In 1836 the timber roof at Chartres cathedral burned spectacularly. In fact that event seems to have unfolded exactly like the Notre-Dame fire weeks ago, starting with a construction accident. At Chartres, the roof structure was rebuilt in iron, with copper roofing. Built in 1837, it is one of the oldest iron structures in France. Few visitors know this; from every accessible point of view, the roof appears medieval. Nobody (as far as I can tell) regards this as controversial. Henry Adams didn’t mention it at all!

Chartres x2.jpg

Automated Design

A new article by Lance Hosey asks: “Can Machines Design?” And it asks: “How might architecture change if computers take over the process entirely?”

I wrote about this in 2011:

“One might imagine a user-friendly device where the customer simply inputs information about the architectural program and some performance criteria; the tool could (invisibly) download site information and code requirements, then generate a variety of alternative designs optimized to the performance criteria. The user would choose his preferred option, and the process could repeat at another level of resolution, eventually including the full engineering of mechanical and structural systems—would you like concrete or steel? Clash detections, costing and scheduling, construction documents, all built in. Call it the iPlan. (The technology is not far off.) Clearly such a passive role is intolerable to architects and engineers, and those who educate them. The ability to choose and control the tools is fundamental to professionalism in the AE disciplines (for now).”

So I do believe that machines can design. Whether architects can tolerate it, is probably an irrelevant question in the long run, if such methods prove to be efficient and useful.

I could also imagine an automated design program having an architect-like avatar guiding clients through the process. You could work with Frank Lloyd Wright or Eero Saarinen someday!

Cite: Anthony Denzer and Jon Gardzelewski (2011). “Drawing and Modeling: Analog Tools in the Age of BIM,” AEI 2011: Building Integration Solutions (American Society of Civil Engineers): 44-53.

Calculating Solar Heat in the 1930s

One of the key themes of The Solar House is that both passive and active solar heating began to be scientifically understood in the 1930s & 40s. Hoyt Hottel and his team at MIT calculated solar heat in about 1939 for (what was later called) MIT Solar House I, which used solar-thermal panels on the roof. Then they wrote the equations used by solar engineers going forward. Meanwhile in Chicago, George Fred Keck and his brother William calculated (passive) solar gains for the Sloan house in early 1940. They found that the gains outweighed the losses for the south-facing glass walls, and in fact they found a net “overload,” indicating possible overheating. Additionally, it was in the 1930s that architects using glass in hot climates began to be concerned about overheating and solving that problem through shading (see Le Corbusier and the Sun for example).

So the question arises: If you wanted to calculate solar gains in, say, 1940, what kind of data and methods were available? If you were doing scientific research, like Hottel and his team, you used meteorological measurements and worked from first principles. If you were an architect like Keck or Le Corbusier, or a practicing engineer, these are the main sources of information that would have been available:

  • Howard T. Fisher, “A Rapid Method for Determining Sunlight on Buildings,” Architectural Record 70 (December 1931), 445-454.

  • R. A. Miller and L. V. Black, "Transmission of radiant energy through glass.” ASHVE Transactions 38 (1932), 63-78.

  • H.E. Beckett, “Orientation of Buildings,” Journal of the Royal Institute of British Architects 40 (1933), 61-65.

  • P.J. Waldram, “Universal Diagrams” Journal of the Royal Institute of British Architects 40 (1933), 50-55.

  • F.C. Houghten, C. Gutberlet, and J.L. Blackshaw, “Studies of solar radiation through bare and shaded windows,” ASHVE Transactions 40 (1934), 101-116.

  • Henry N. Wright, “Site Planning and Sunlight,” American Architect and Architecture 149 (August 1936): 19ff.

  • Arthur M. Greene, Principles of Heating, Ventilating and Air Conditioning (1936)

  • “Figuring Solar Heat Gains of Buildings” by William Goodman, in Heating, Piping, and Air Conditioning, May through October 1938

  • “Orientation for Sunshine,” Architectural Forum, June 1938

Jacobsen's SAS Hotel: Facade issues

Arne Jacobsen’s SAS Hotel in Copenhagen was originally built in 1958–60, and it is widely-acknowledged as a masterpiece of mid-century modernism.

©  Anthony Denzer

© Anthony Denzer

The curtain wall is leaking water pretty badly; I experienced this when I stayed here a few weeks ago. I found this note from the hotel, which says that they are “working on” finding a solution which is sensitive to the building’s protected status. Does this mean a major facade renovation is being planned? Unclear.

©  Anthony Denzer

© Anthony Denzer

Because of the deep marble sills, the water didn’t cause any issues within the room, but you can bet there are unseen problems occurring. My stay there was wonderful. Here’s a few more pictures.

©  Anthony Denzer

© Anthony Denzer

©  Anthony Denzer

© Anthony Denzer

Final note: I find the black columns in the image above to be much too visually strong. Originally they were white. The lobby was renovated in 2017–18 by Space Copenhagen and Fritz Hansen.

Solar Form in the 70s

Last week at the Architectural Engineering Institute (AEI) conference I presented a paper called “The Solar Architecture Taxonomy: A Historical Analysis.” My co-author Jon Gardzelewski and I analyzed 180 solar buildings from the 1970s to see how architects used solar panels when they became commercially-available for the first time. There is very little design theory addressing solar panels. We presume this might have value for designers who wish to use PV in the future.

We found the most common design strategy was to create ‘solar form’—to shape (or distort) the building form so that panels face the south sky. 72% of the 180 buildings in our survey had solar form. In our reading, this design strategy is derived from early-modernist theory (“form follows function”).

We further distinguished between “strong form” and “weak form.” Here’s what we wrote:

…we propose to define strong form as follows: the major form clearly expresses the collection of solar energy, plus the minor forms and other design elements directly support the same theme.  We suggest weak form for buildings that have a major gesture which expresses the collection of solar energy, but other forms and elements which communicate other priorities or influences.”

AEI 2019 Denzer.jpg

To distinguish between strong form and weak form does not necessarily imply a value judgment.  Some examples of strong form are strongly eccentric; they look dated in retrospect.  Some examples of weak form certainly represent sophisticated design thinking, as they reflect the influence of Postmodern architectural theory in the 1970s, where the expression of “complexity and contradiction” (Venturi, 1966) became a positive goal for architectural design. 

Other examples of weak form—typically housesare compromised by an apparent desire to ‘fit in’ to a traditional vocabulary, or to simply not appear eccentric. The magazine Popular Science found “researchers … were trying to make their projects look as much like other houses on the block as possible” (Luckett, 1974).

Previously on the blog:
A note on the solar architecture of the 1970s